bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonia Emission from Soybean‐Amended Calcareous Soil with Various Soil Temperature and Moisture Levels
Authors: O'Deen W. A. , Follett R. F.
Published: July 2010

High soil temperature, moisture, and crop residue levels were found to combine for maximum volatilization of ammonia from calcareous soil amended with soybean [Glycine max (L.) Merr.] tissue in this study. An unusually large amount of ammonia was liberated to the atmosphere and provided the opportunity to measure accurately isotope separation of 15N and 14N atoms resulting from the diffusion process. Soybean tissue (early reproductive stage) was mixed with a calcareous soil (Aridic Paleustoll) at two different levels (25 and 50 g kg−1). The two soil soybean‐tissue mixtures were wetted to the desired moisture content (20, 60, and 100% field capacity) and incubated 7 d at either 10, 20, or 30 °C. After incubation, ammonia evolution and moisture loss were determined during either a 4‐ or 7‐d dry‐down period in which dry NH3‐free air was passed across the soil surface. We found more NH3 volatilized at 100ɐ FC than at 20 or 60% FC, at 30 than at 10 or 20 °C, and at 50 than at 25 g kg−1 residue rate. Maximum loss of NH3 was about 5% of soybean‐tissue N measured in an experiment in which four wet‐dry cycles were used. Maximum loss was directly related to water evaporation rate. These results indicate that soil temperature, moisture, and crop‐residue rates all influence NH3 losses from soybean‐tissue amended soil. Isotopic ratios of the NH3−N evolved were measured and ammonia content of the first fraction of ammonia volatilized was lower in atom % 15N than the last fraction. These results indicate that, for the conditions of this study, diffusion is an important process since the 14N atoms volatilized more quickly as NH3 than did the 15N atoms.
Alfalfa Development after Simulated Alfalfa Weevil Injury
Authors: Peterson Robert K. D. , Danielson Stephen D. , Higley Leon G.
Published: July 2010

Although the alfalfa weevil [Hypera postica (Gyllenhal)] is an important insect pest of alfalfa (Medicago sativa L.), relatively little is known about how larval defoliation affects growth processes at specific developmental stages. This study was conducted to characterize the developmental responses of alfalfa to simulated alfalfa weevil injury when injury was initiated at the early‐bud stage of the first growth cycle. The study was conducted on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic, Typic Argiudolls) in a 3.6 ha ‘Haymaker’ alfalfa field near Walton, NE. A total of 16 1‐by 1‐m plots were arranged in a randomized complete block design with four treatments in each of four replicates. Treatments consisted of an undefoliated check and three levels of simulated alfalfa weevil defoliation. Morphological effects of simulated alfalfa weevil injury were determined at five postdefoliation periods. Leaf area indices, leaf area to total dry weight ratios, and leaf dry weight to total dry weight ratios were reduced linearly as defoliation percentages increased. However, defoliation injury did not affect phenological development of the first growth cycle between the completion of injury and first harvest. Most growth rates were not different among treatments, indicating that there was no postdefoliation compensatory growth. Injury initiated at the early‐bud stage of the first growth cycle did not impact alfalfa regrowth after the first harvest. Consequently, the most important effect of defoliation initiated at the early‐bud stage of the first growth cycle was to reduce dry matter yield of the first growth.
Growth of Peanut Roots under Field Conditions
Authors: Ketring D. L. , Reid J. L.
Published: July 2010

The largest detriment to crop productivity in many environments is available water. Biomass accumulation is proportional to water moving through the plant, i.e., transpiration. The supply of water for crop biomass accumulation is provided from the soil reservoir by the root system. Our objective was to quantify peanut (Arachis hypogaea L.) root growth over time by depth and lateral spread in the soil profile. By soil coring techniques, we determined the growth of roots, in response to irrigation treatments imposed under field conditions, of two Virginia‒, runner‐type peanut cultivars over time. Root length density (RLD) and root weight density (RWD) in the soil profile were not significantly different between cultivars or among irrigation treatments. However, significant year differences were observed. Following crop establishment under similar environmental conditions in both years, 1988 was hotter and drier than 1989. Also, postplant rainfall through 45 DAP was less in 1988 than 1989 and total water received by the crop was less in 1988 than 1989. Under these conditions, there was nearly twice and three times as much RLD and RWD in 1988 than 1989. Root length density and RWD significantly increased at each depth increment with days after planting (DAP) until 80 DAP. At 40 to 45 DAP, roots had penetrated to a depth of 120 cm and spread laterally to at least 46 cm (mid‐furrow). The 15‐cm depth increment had the highest mean RLD, which increased to a maximum at 2.1 and 1.7 cm cm−3 at 80 and 83 DAP in 1988 and 1989, respectively. However, over the same time period there was also a simultaneous increase in RLD at depths below 15 cm. Thus, peanut roots were established both deeply and laterally in the soil profile early in the growing season. This could prove advantageous in a drought environment and the knowledge useful for water management of the crop.
Light Transmittance, Soil Temperature, and Soil Moisture under Residue of Hairy Vetch and Rye
Authors: Teasdale J. R. , Mohler C. L.
Published: July 2010

Cover crop residue on the surface of soils in no‐tillage systems can suppress weed emergence and growth. Although allelopathy often is invoked to explain weed suppression by residue, physical alterations of the seed environment could be important as well. This experiment was conducted to determine the light, temperature, and moisture conditions under cover crop residue. Hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) were desiccated with a contact herbicide and residue rates ranging from one‐fourth to four times the natural residue biomass were established in experiments at Beltsville, MD and Ithaca, NY. Photosynthetic photon flux density (PPFD) was determined above and below residue at approximately monthly intervals after initiation of the experiment. Transmittance of PPFD through residue declined according to an exponential decay function of residue biomass. Transmittance was similar through hairy vetch and rye residue initially, but as the experiment progressed, transmittance through hairy vetch residue was greater than that through rye because of faster decomposition of hairy vetch residue. Spectral analysis from 400 to 1100 nm showed a slight increase in transmittance as wavelength increased resulting in a slight lowering of the red (660 nm) to far‐red (730 nm ratio relative to that of unobstructed sunlight. Soil maximum temperature and daily soil temperature amplitude were reduced by cover crop residue. Residue prevented the decline of soil water content during droughty periods. Results indicated that reductions in light transmittance and daily soil temperature amplitude by cover crop residue were sufficient to reduce emergence of weeds but that maintenance of soil moisture could increase weed emergence.
Nitrogen Efficiency Component Analysis: An Evaluation of Cropping System Differences in Productivity
Authors: Huggins D. R. , Pan W. L.
Published: July 2010

The development of cropping systems that use N efficiently requires methods that evaluate system differences in N use. A procedure, based conceptually on soil and plant processes that affect N use, was developed to evaluate differences in N use efficiency among cropping systems. The method uses measurements of yield, grain N, aboveground plant N, applied N, and postharvest inorganic soil N to partition cropping system differences in yield and grain N into N efficiency components. The components consist of N supply, available N efficiency, available N uptake efficiency, N utilization efficiency, grain Naccumulation efficiency, and N harvest index. The N efficiency component analysis was demonstrated for a field study with hard red spring wheat (Triticum aestivum L. ‘WB 906R’) where conventional tillage had a greater yield and grain N than no‐tillage. At low N rates, 78% of the difference in yield between the two was attributed to N supply and available N efficiency components. At high levels of applied N, 88% of the yield difference was attributed to the N utilization efficiency component. Differences in grain N were attributed to N supply and available N efficiency components, whereas components of grain N accumulation efficiency, available N uptake efficiency, and N harvest index were nonsignificant. Overall, this new approach transcends empirical analyses and provides insight into underlying mechanisms of cropping system differences in N use.
Quantifying Wheat Water Stress with the Crop Water Stress Index to Schedule Irrigations
Authors: Garrot Donald J. , Ottman Michael J. , Fangmeier D.D. , Husman Stephen H.
Published: July 2010

The relationship between the timing and amount of applied irrigation water and grain yield has not been well defined for durum wheat (Triticum turgidum L. var. durum) grown under irrigation in arid regions. With rising water costs and decreasing water supplies, grain growers will have to optimize yield for given levels of water inputs if they are to remain profitable. Small‐plot field studies were conducted in 1986 and 1987 at Marana, AZ, to (i) test the feasibility of using the crop water stress index (CWSI) to schedule wheat irrigations and (ii) determine relationships among CWSI, grain production, and water applied. Highest grain production was attained when irrigations were scheduled at CWSI values averaging 0.37 units in 1986 and 0.30 units in 1987. Scheduling irrigations with lower CWSI values did not increase grain production, but required more water. Delaying irrigation by scheduling irrigations at CWSI values exceeding the optimum values reduced grain production.
Management and Environment Effects on Brassica Forage Quality
Authors: Wiedenhoeft M. Hagemann , Barton B. A.
Published: July 2010

Forage Brassica spp. have been shown to produce adequate amounts of herbage during the cooler months of the fall, thus allowing extension of the grazing season in higher latitudes. The objective of this study was to determine if the nutritive quality of initial and regrowth herbage was influenced by planting and harvest date. In 1987, 1988, and 1989, three Brassica spp. (rape [B. oleracea L.], turnip [B. rapa L.] and turnip hybrid [B. rapa L. × B. pekinensis L.]) were planted in late May to early June, late June to early July, and late July to early August and were harvested each year at 64, 76, or 85 DAP. The plants regrew 60, 70, or 80 d and were harvested. Nutritive components measured were CP, NDF, ADF, Ca, Mg, and P. Nutritive levels declined with warmer temperatures and low soil moisture levels particularly during July and August. Neutral‐detergent fiber and ADF levels were higher, while the CP levels were lower in herbage from the earliest planting date compared with the later planting dates, regardless of species and year. The levels of Ca, Mg, and P were influenced by species and planting date. In general, the regrowth herbage had a lower fiber and a higher protein content than the initial herbage. The variation in nutritive quality among the three species was relatively small. Of more importance to the producer is that the quality of brassica herbage is more comparable to a concentrate than a traditional forage because of the relatively low fiber and high protein content.
Ethephon Alters Corn Growth, Water Use, and Grain Yield Under Drought Stress
Authors: Kasele I. N. , Nyirenda F. , Shanahan J. F. , Nielsen D. C. , d'Andria R.
Published: July 2010

The plant growth regulator ethephon has been used to reduce height and lodging of intensively managed corn (Zea mays L.). However, the impact of ethephon‐induced changes in vegetative growth on water use and grain yield of corn grown at various densities under drought stress conditions has not been widely studied. Field studies were conducted for 2 yr in semiarid eastern Colorado to determine if foliar ethephon application can alter vegetative growth and water use and promote drought stress resistance of corn. In 1989, treatments consisted of a factorial combination of two irrigation levels (low and high), two plant densities (53 333 and 80 000 plants ha−1), and five ethephon treatments (0, 0.28, 0.56, and 0.84 kg ha−1, applied at the 6‐ or 8‐leaf growth stage) at one site. In 1990, treatments consisted of a factorial combination of four plant densities (24 700, 37 045, 49 390, and 61 735 plants ha−1) and three ethephon rates (0, 0.28, and 0.56 kg ha−1 applied at the 6‐leaf stage) at two sites. Plant height, leaf area index (LAI), dry matter yield, cumulative evapotranspiration (ET), and grain yield were measured. In both seasons, ethephon application reduced plant height and LAI by 10 to 40%, relative to the control, and this resulted in early season ET reductions. Ethephon application either had no effect or decreased yields in 1989 under all irrigation and plant density treatments, because of a lack of significant drought stress. However, when drought occurred in 1990, ethephon application decreased yields at low plant densities but enhanced yields at high plant densities at both locations, with a maximum 37% yield increase for the intermediate ethephon rate. Our data indicate that ethephon application has the potential for improving resistance to drought in corn.
Nitrogen Fertilizer Application and Seeding Date Effects on Oat Grain Milling Quality
Authors: Humphreys D. Gavin , Smith Donald L. , Mather Diane E.
Published: July 2010

Management factors such as N fertilizer rate and seeding date can significantly influence oat (Avena sativa L.) grain milling quality. The effects of N fertilizer and seeding date on the grain yield and milling quality of four oat cultivars were evaluated using two N rates (40 kg ha−1 applied at seeding or 40 kg ha−1 applied at seeding plus 20 kg ha−1 applied at the boot stage) and two seeding dates. Studies were conducted at Ste‐Anne‐de‐Bellevue, PQ, Canada, from 1990 to 1992 and at Ste‐Rosalie, PQ, in 1991. Nitrogen treatments had little effect on milling quality at Ste‐Anne‐de‐Bellevue, but hull percentage decreased and plump grain percentage increased with higher N in the Ste‐Rosalie experiment. Delayed seeding reduced yields in all four experiments. In the Ste‐Anne‐de‐Bellevue experiments, delayed seeding reduced test weight, 1000‐grain weight, plump grain percentage, and theoretical milling yield and increased percentage of hull, thin grain, and bosom grain. In the Ste‐Rosalie experiment, opposite effects were observed; this may have resulted from reduced production of secondary and tertiary seeds in the late‐seeded treatments. For most milling quality characteristics, significant differences between cultivars were observed, and cultivars interacted with management treatments. In general, the higher application rate of N did not improve oat grain milling quality sufficiently to warrant its usage. Later seeding resulted in inferior yields at all locations, but did not necessarily reduce milling quality. The correct choice of cultivar seems crucial for production of high‐quality milling oat grain.
Leaf Emergence on Potato Stems in Relation to Thermal Time
Authors: Cao Weixing , Tibbitts Theodore W.
Published: July 2010

For simulation of foliar development of potato plants (Solanum tuberosum L.), it is necessary to quantify the responses of leaf emergence to major environmental factors. This study was conducted to determine the relationship of leaf emergence on potato stems to growing degreedays (GDD) under varied temperature patterns over different growth periods. In each of two duplicate experiments in controlled environments, potato plants were grown for 63 d after transplanting of tissue culture plantlets into 20‐L pots containing peat‐vermiculite mix. Four treatments were maintained, involving two constant temperatures of 17 and 22°C and two changed temperatures of 17‐22‐17 and 22‐17‐22°C over three 21‐d periods under constant vapor pressure deficit of 0.60 kPa and photosynthetic photon flux density of 430 µmol m−2 s−1 for a 14‐h photoperiod. The first period was the first 21 d of plant growth after transplanting, the second 21‐d period coincided with plant enlargement and tuber initiation, and the third period coincided with tuber enlargement. Leaf numbers on main stems and uppermost apical branches were recorded every 2 to 3 d during the course of the experiments. This leaf number increased linearly with accumulated GDD over the whole experiment duration for each of the four treatments, whether the temperature was constant or changed. The phyllochron in GDD per leaf (6°C base temperature) was lowest at constant 17°C (19.2 GDD), highest at constant 22°C (22.8 GDD), and intermediate at the changed temperatures ( ≈21.3 GDD). Detailed analysis of the leaf emergence rates during each of the three 21‐d periods indicates that the phyllochron at either 17 or 22°C was also slightly lower during the second 21‐d period than during the first and third 21‐d periods. The total leaf number increased with increasing total GDD among the treatments, primarily from varied leaf number on apical branches. The data suggest that a constant phyllochron for a given growth location and calendar time may provide sufficient accuracy for predicting leaf emergence on potato stems in the field environment.
Water and Nitrogen Effects on Winter Wheat in the Southeastern Coastal Plain: I. Grain Yield and Kernel Traits
Authors: Frederick James R. , Camberato James J.
Published: July 2010

Understanding how environmental factors affect winter wheat (Triticum aestivum L. emend. Theil.) responses to spring N application is an important component of economically and environmentally sound winter wheat production on the southeastern Coastal Plain of the USA. Increasing the amount of N applied to winter wheat grown in this region has been shown to result in a greater severity of drought stress during grain fill and lower individual kernel weights. This 2‐yr field study was conducted to determine whether drought‐induced reductions in kernel weight with high spring N rates are the result of decreases in the rate or the duration of kernel growth. Winter wheat was grown with different rates of spring‐applied N (0, 45, 90, and 135 kg N ha−1) under both irrigated and nonirrigated conditions. Increases in the rate of springapplied N resulted in a greater severity of soil water deficits under nonirrigated conditions. Quadratic increases in grain yield and kernel number per square meter occurred in response to increased spring N under both levels of soil water treatment. Grain yield and individual kernel weight responses to irrigation were greater at the higher N rates than at the lower N rates. Over both years, the average increase in individual kernel weight due to irrigation was 3.9 and 13.3% at the 0 and 135 kg N ha−1 rates, respectively. Similar responses were found for the effective filling period (EFP), where irrigation increased the EFP an average of 3.2 and 14.5% at the lowest and highest spring N rates, respectively. Soil water treatment had no effect on kernel growth rate. Results indicate that high rates of spring‐applied N increase the severity of drought stress in nonirrigated winter wheat grown on the Coastal Plain, resulting in reductions in the EFP and, consequently, kernel weight.
Comparison of Normal and Opaque‐2 Maize Genotypes Used for Corn Cob Mix in Pig Feeding
Authors: Pintér Lajos , Burucs Zoltán , Alföldi Zoltán
Published: July 2010

Opaque‐2 (o2) maize (Zea mays L.) contributed significantly to the quality improvement of maize breeding in the 1960s, but did not become popular because of a lower yield, a result of its shorter grain‐filling period. This characteristic, however, could prove to be advantageous for use in corn cob mix (CCM), which is popular in the cold‐wet regions of Europe. A research program including a 3‐yr field trial, an in vivo pig (Sus scrofa) study with fermented CCM, and a farm‐scale fattening test was conducted to evaluate the prospect of o2 for CCM production and utilization. Opaque‐2 yielded as much CCM at the CCM ripening stage (600 g kg−1 grain DM) as did the normal version. Due to its shorter grain‐filling period, 02 can accumulate more assimilates at a higher grain moisture content than the normal maize. Results from in vivo pig trials showed that o2 was superior in N retention and in the biological value of protein compared with the normal genotype. Consequently, using o2 can balance the feed value and reduce the soybean [Glycine max (L.) Merr.] content in the ration for fattening pigs by 27%. The quality of the meat of slaughtered pigs fed with o2 and less soybean was comparable to that of pigs fed with normal maize and larger supplement of soybean protein. Improved o2 genotypes may be an alternative source of CCM production in countries where the climate is not very favorable for soybean production and where alternative protein supplements are not readily available.
Crop and Nitrogen Yield in Legume‐Based Rotations Practiced with Zero Tillage and Low‐Input Methods
Authors: Izaurralde R. C. , Juma N. G. , McGill W. B. , Haderlein L. , Choudhary M.
Published: July 2010

Though legumes are beneficial in crop rotations, there is limited information on how tillage system‐crop sequence interactions influence crop yield and N production. To see if biomass and N yields in short‐term legume‐based rotations under zero tillage (ZT) and low‐input (LI) production methods can equal those in cereal monocultures under ZT and conventional tillage (CT), field experiments were conducted in Alberta, Canada, from 1989 to 1992 at Ellerslie (Typic Cryoboroll soil) and Breton (Typic Cryoboralf). Treatments at each site consisted of (i) two 4‐yr rotations, each with the same crop sequence but different tillage methods, and (ii) four continuous barley treatments in 2 ✕ 2 factorial combination of tillage and fertilizer N. The crop sequence was barley (Hordeum vulgare L.)‐barley and field pea (Pisum sativum L.) intercrop‐barley‐fababean (Vicia faba L.). At Ellerslie, tillage for weed control and seedbed preparation was either CT‐LI or ZT. At Breton, one rotation used the LI approach; the second used deep tillage (DT). Weeds on CT and ZT were controlled with either pre‐ or postemergence herbicides. No herbicides were applied to LI treatments at either site or to the DT treatment at Breton. Yields of barley following legumes under ZT were similar to those of fertilized continuous barley. With nonchemical weed‐control methods, weed competition reduced yields of barley following legumes by 24% compared with fertilized continuous barley. The increased fababean yield measured under DT was associated with improved rooting conditions and water extraction. The equivalent N‐fertilizer value of legume residues with similar weed‐control levels averaged 19 kg ha−1. Except for the LI system, legume‐based rotations produced, over the 4‐yr cycle, amounts of N equivalent to continuous cereal systems. Resource use efficiency of legume‐based rotations, as measured by net‐N yields, was equivalent to continuous systems at Breton, but somewhat reduced at Ellerslie.
Wheat Response to Row Spacing in Relay Intercropping Systems
Authors: Porter Paul M. , Khalilian Ahmad
Published: July 2010

Relay intercropping of soybean [Glycine max (L.) Merr.] or cotton [Gossypium hirsutum L.] into standing wheat [Triticum aestivum L.] allows for earlier planting of the summer crop than with sequential double‐crop systems. Relay intercropping has been evaluated using modifications of standard planting and harvesting equipment as well as specifically designed equipment. In most relay intercropping systems, wheat is drilled in the fall in a row pattern that provides traffic‐tire lanes as guides for planting the summer crop. Also, row spacing for wheat in relay intercropping is usually wider than for conventionally planted wheat. This field study, conducted during 1991‐1992 and 1992‐1993 near Blackville, SC, on a Varina loamy sand (clayey, kaolinitic, thermic Plinthic Paleudults), compared the yield and yield component response of soft red winter wheat produced with two different intercropping production schemes to the yield and yield component response of conventionally planted wheat. Yields of wheat planted in skip‐row schemes designed to allow for relay intercropping of either soybean or cotton were not significantly different from yield of conventionally planted wheat under the given experimental conditions. For conventionally planted wheat, wheel traffic on certain rows reduced yields by as much as 50% compared with nontraffic rows. In the schemes designed to allow for relay intercropping, wheat grown with wider‐spaced rows (0.31‐0.61 m) compensated with respect to yield on an area basis compared with wheat grown with conventionally spaced rows (0.15‐0.20 m).
Dynamics of Moisture, Nitrogen, and Striga Infestation on Pearl Millet Transpiration and Growth
Authors: Boukar Ibrah , Hess Dale E. , Payne William A.
Published: July 2010

The parasitic weed Striga hermonthica (Del.) Benth. (witchweed) is a major biotic constraint to pearl millet [Pennisetum glaucum (L.) R. Br.] production in Sahelian Africa. To address this constraint, more information is needed on host‐parasite relations under varying conditions of soil water and nutrient availability typically found in the Sahel. The dynamics of moisture, N, and Striga infestation on pearl millet transpiration and growth were investigated. The effects of Striga infestation, water deficit stress, and N availability on root length and dry weight, shoot dry weight, and transpiration ratio (TR; g dry matter kg−1 transpiration) were evaluated. Millet was grown in 36‐L pots for 45 d in a glasshouse, using two levels of water and N availability and three levels of Striga infestation. With no N, shoot dry weight of uninfested millet plants was low. Shoot weight was further reduced by 42% at the high level (71 000 seeds pot−) of Striga infestation. With the addition of 60 kg ha− of N, shoot weight of uninfested millet plants increased five‐ to sixfold. A reduction of 36% in shoot weight was observed in plants with N and highest infestation of Striga. Root dry weight was also low without N, but unaffected by Striga infestation. With the addition of N, root dry weight of millet plants increased under adequate and water‐stressed conditions. Root length in the upper 0.10 m followed a similar trend. Transpiration ratio decreased due to Striga infestation, increased with reduced water availability, and increased with greater N supply. The number of Striga haustoria attached to millet roots increased with water deficit stress, N addition, and increased level of infestation. The number of haustoria per unit root length increased with water stress and Striga infestation, but was substantially decreased by N addition. The number of haustoria per unit root length increased linearly with the total number of haustoria present. This slope was independent of water supply, but was four times greater for unfertilized plants compared with those receiving N. This study confirms that Striga attack is more severe in the presence of nutrient and water stress, and reduces whole‐plant water‐use efficiency. It also suggests a physiological mechanism by which N addition permits the host to better resist Striga attack.
Temporal Changes in Soybean Gas Exchange Following Simulated Insect Defoliation
Authors: Peterson Robert K. D. , Higley Leon G.
Published: July 2010

Characterizing the influence of arthropods on plant gas exchange processes, such as photosynthesis, water‐vapor transfer, and respiration, is important because these processes are crucial determinants of plant growth, yield, and fitness. Despite the relatively extensive research that has been conducted on physiological responses of soybean [Glycine max (L.) Merrill] to defoliation injury, transient gas exchange parameters, such as photosynthesis, stomatal conductance, and respiration, have not been measured to determine if they are altered after the injury process. A better understanding of these responses would improve the development of plant response models to arthropod stress, which are needed to determine economic injury levels used in pest management programs. Therefore, this study was conducted to characterize the gas exchange responses of soybean following leaf‐mass consumption. The study was conducted from 1992 through 1994 on soybean (‘Kenwood’ and ‘Clark’) in a field environment. The experimental design was a randomized complete block with six replications in 1992, four replications in 1993, and seven replications in 1994. Rows were the blocking factor. Various defoliation treatments were imposed using a cork‐borer punch. Each treatment replicate was assigned to a leaflet on a separate plant. Gas exchange parameters were measured using a portable photosynthesis system and a steady‐state porometer. At approximately 0.25, 1, 3, and 24 h after injury, gross tissue removal did not affect gas exchange parameters of soybean leaflets. Our results support previous research indicating that gross tissue removal does not appreciably alter photosynthetic rates of injured soybean leaves.
Lower Limit of Soil Water Availability
Authors: Savage Michael J. , Ritchie Joe T. , Bland William L. , Dugas William A.
Published: July 2010

Estimating the available soil water reservoir is needed for developing a strategy for optimum management of rainfed crops in marginal dry regions. Previous research on measurement of the lower limit water content of soil water availability (required for calculation of the total soil water reservoir) has shown unexplained discrepancies between field estimates of the water content at which plants are dead or dormant due to soil water deficit and laboratory estimates of the water content at a water potential of − 1.5 kJ kg−1. Whether such discrepancies are due to sample size, handling, or the choice of − 1.5 kJ kg−1 as the lower limit is not clear. This study was designed to determine what the limit is under controlled conditions, and to test the appropriateness of the −1.5 kJ kg−1 value. We used in situ soil psychrometers to measure soil water potential (Ψ) as water was withheld from cotton (Gossypium hirsutum L.) plants in a rain‐sheltered lysimeter monolith and from sorghum [Sorghum bicolor (L.) Moench] in glasshouse pots. The lower limit Ψ was − 2.2 kJ kg−1 in the lysimeter experiment and < − 2.5 kJ kg−1 in the glasshouse. With the lysimeter, the difference between the soil water content corresponding to − 2.2 kJ and − 1.5 kJ kg−1 was <0.01 m3 m−3. Water potential at the greatest measurement depth (2.1 m) decreased rapidly from near 0 to − 1.8 kJ kg−1 over a period of 30 d, while root length density increased from nearly 0 to 2400 m−3. At an advanced stage of soil water deficit, there was limited upward movement of water from depths >2.1 m. No Ψ oscillations, corresponding to so‐called hydraulic lift or nocturnal water transport between soil layers, were found at any depth in the lysimeter (0.5–2.1 m). Our results suggest that for water balance calculations requiring absolute accuracy for the water balance of the soil reservoir, the choice of the − 1.5 kJ kg−1 soil water potential is appropriate and corresponds closely to the field lower limit of soil water availability.
Simulating Maize Emergence Using Soil and Climate Data
Authors: Weaich Karl , Bristow Keith L. , Cass Alfred
Published: July 2010

Experimental programs aimed at improving seedling establishment in the semiarid tropics require quantitative information concerning the interaction between the seedbed environment and preemergent seedling growth. The model here described links a soil heat and water model, a soil strength model, and a temperature‐dependent maize (Zea mays L.) shoot growth model to predict the response of preemergent maize seedlings to a physical environment typical of the semiarid tropics. In comparisons with field measurements taken in the semiarid tropics under high drying rate conditions, the model simulations yielded accurate representations of soil water, temperature, strength, and preemergent shoot growth of maize. The model was also used to compare the effects of radiation‐ vs. wind‐dominated evaporative demand on preemergent seedling growth in a hardsetting seedbed. Results showed that under radiation‐dominated conditions, the early onset of high soil temperature limited seedling growth, while under wind‐dominated conditions, the early development of high soil strength affected seedling growth first. Simulations using surface mulch as an ameliorative management practice showed that mulch greatly reduced soil evaporation, thereby eliminating high soil strength as a limitation to seedling establishment. Results indicate that the model is a potentially useful tool for investigating the likely effects of soil and climate on seedling emergence.
Simulation Models: Science, Snake Oil, Education, or Engineering?
Authors: Passioura John B.
Published: July 2010

Crop simulation models can be divided into two groups: those that aspire to improve our understanding of the physiology and environmental interactions of crops (science), and those that aspire to provide sound management advice to farmers or sound predictions to policy makers (engineering). These quite different aspirations require quite different models. Scientific models are mechanistic. With a few exceptions, they have failed to meet their aspirations. They are typically flawed by being based on untestable guesses about the processes that control growth. They may, however, provide useful self‐education for their developers. The best engineering models are based on robust empirical relations between plant behavior and the main environmental variables. Because of their empirical nature, we should not expect them to apply outside the range of the environmental variables used in their calibration. Within their calibrated ranges, however, some have proved useful in providing sound management advice. It is hard to see a useful role, other than self‐education, for models that fall between the scientific and the engineering types.
Critical Light Interception during Seed Filling for Insecticide Application and Optimum Soybean Grain Yield
Authors: Board James E. , Wier Alan T. , Boethel David J.
Published: July 2010

Relationships between defoliation, light interception, and grain yield for soybean [Glycine max (L.) Merr.] during the last half of the seed filling period are not fully understood. Because defoliating insect pests in the southeastern USA frequently attack soybean during this period, knowledge of such relationships would aid development of criteria for economic insecticide application. Our first objective was to determine the efficacy of using light interception and leaf area index as criteria for economic insecticide application to manage defoliating insect pests. The second objective was to determine the effects of partial and total defoliations during seed filling on grain yield and grain yield formation. ‘Centennial’ soybean (Maturity Group VI) was planted in 1993 and 1994 near St. Gabriel, LA. Experimental design was a randomized complete block in a split‐plot arrangement. Main plots were the temporal midpoint and 3/4‐point seed‐filling stages. Split plots were four defoliation treatments: 0% leaf removal (control), 37 to 41% leaf removal, 56 to 61% leaf removal, and 100% leaf removal. At the temporal midpoint, grain yield declined linearly as light interception fell from 93 to 50%. Thus, for a crop achieving near‐maximal light interception, insecticide application would be recommended whenever light interception at the midpoint seed‐filling stage fell below 93%. Yield and light interception were not closely related at the 3/4‐point seed‐filling stage. Maintenance of maximal grain yield (yield at 0% defoliation) required retention of at least 39% of the leaf area at this time. In conclusion, light interception potentially could be used as an insecticide application criterion at midpoint seed‐filling stage, but not the 3/4‐point. Partial defoliation at the midpoint will affect grain yield if it reduces light interception below 93%, whereas at the 3/4‐point total defoliation is required to affect grain yield.
Evaluation of Two Maize Models for Nine U.S. Locations
Authors: Kiniry Jim R. , Williams Jimmy R. , Vanderlip Richard L. , Atwood Jay D. , Reicosky Donald C. , Mulliken Jerry , Cox William J. , Mascagni Henry J. , Hollinger Steven E. , Wiebold William J.
Published: July 2010

Crop models can be evaluated based on accuracy in simulating several years' yields for one location or on accuracy in simulating long‐term mean yields for several locations. Our objective was to see how the ALMANAC (Agricultural Land Management Alternatives with Numerical Assessment Criteria) model and a new version of CERES‐Maize (Crop‐Environment Resource Synthesis) simulate grain yield of rainfed maize (Zea mays L.). We tested the models at one county in each of nine states: Minnesota, New York, Iowa, Illinois, Nebraska, Missouri, Kansas, Louisiana, and Texas (MN, NY, IA, IL, NE, MO, KS, LA, and TX). Simulated grain yields were compared with grain yields reported by the National Agricultural Statistical Service (NASS) for 1983 to 1992. In each county we chose a soil commonly used in maize production, and we used measured weather data. Mean simulated grain yield for each county was always within 5% of the mean measured grain yield for the location. Within locations, measured grain yield was regressed on simulated grain yields and tested to see if the slope was significantly different from 1.0 and if the y‐intercept was significantly different from 0.0, both at the 95% confidence level. Only at MN, NY, and NE for ALMANAC and at MN, NY, and TX for CERES was slope significantly different from 1.0 or intercept significantly different from 0.0. The CVs of simulated grain yields were similar to the those of measured yields at most sites. Also, both models were appropriate for predicting an individual year's yield for most counties. Values for plant parameters, such as heat units for development and the harvest index, and values for soil parameters describing soil water‐holding capacity offer users reasonable inputs for simulating maize grain yield over a wide range of locations.
Residue Management and Minimum Tillage Systems for Soybean following Wheat
Authors: Vyn Tony J. , Opoku George , Swanton Clarence J.
Published: July 2010

The acceptance of no‐till systems for soybean [Glycine max (L.) Merr.] production following winter wheat (Triticum aestivum L.) on fine‐textured soils in Ontario has been hampered by soybean yield reductions due to unfavorable seedbed conditions. This research was conducted to identify alternative tillage and residue management systems that will enhance emergence, growth, and yield of soybean following winter wheat. Seven tillage and residue management systems, comprising fall moldboard plow, fall chisel plow, fall disk only, fall zone‐till, no‐till, no‐till (with wheat straw baled), and no‐till (with wheat straw and stubble removed), were evaluated following winter wheat on fine‐textured soils from 1994 to 1996 at six different sites near Centralia and Wyoming in southwestern Ontario. Spring soil moisture was lower in the fall tillage treatments than in no‐till with wheat residue, but moisture differences did not vary among fall tillage treatments. No‐till seedbeds had the highest soil moisture contents, the lowest proportion of fine soil aggregates (<5 mm in diameter), and the greatest penetrometer resistance. No‐till soybean growth was delayed and yields were reduced as the level of wheat residue left after planting increased. Soybean seed yield was negatively correlated with surface residue cover, but positively correlated with soil aggregates <5 mm in diameter at all sites. Fall zone‐till and fall disk systems generally improved in‐row seedbed conditions (higher fine soil aggregates and lower soil resistance), and increased seed yields by 5 to 29% relative to no‐till treatments. Fall zone‐till and fall tandem disk systems were the best conservation tillage alternatives to fall moldboard plowing.
Dry Bean and Soil Response to Tillage and Row Spacing
Authors: Xu Chuanguo , Pierce Francis J.
Published: July 2010

Specific studies relating tillage system with performance and yield of dry bean (Phaseolus vulgaris L.) are limited. This study examined how tillage and row spacing affect dry bean development, growth, and yield. The study was conducted on a Parkhill loam (fine‐loamy, mixed, nonacid, mesic Mollie Endoaquepts) from 1989 through 1991. Six tillage treatments (moldboard plow, moldboard plow without secondary tillage, chisel plow, ridge till, no‐tillage, and no‐tillage plus cultivation) and row spacings of 56 and 71 cm were evaluated in a split‐plot design. ‘Mayfiower’ dry bean followed maize (Zea mays L.) in a maize‐dry bean‐sugarbeet (Beta vulgaris L.)‐oat (Avena sativa L.) rotation. Canopy height, trifoliolate leaf number, leaf area, and total biomass of dry bean were measured at three times in 1990 and four times in 1991, and seed yield was measured at harvest. Soil bulk density, total porosity, macroporosity, and saturated conductivity were measured in September of 1989 and 1990. Soil water contents were measured weekly at the 0‐ to 15‐cm, 15‐ to 30‐cm, and 30‐ to 75‐cm depths. In general, there were no interactions between tillage and row spacing over the three years. Dry bean yields in the 56‐cm row spacing were 0.3 to 0.6 Mg ha−1 higher than in the 71‐cm row spacing for all three years. Tillage had no effect on yield in the dry year of 1989, but no‐tillage reduced yields 0.57 and 0.9 Mg ha−1 in 1990 and 1991 compared with moldboard plowing. Ridge tillage and no‐tillage plus cultivation in 1990 and chisel plowing in 1991 also reduced dry bean yields. Tillage affected soil water contents slightly in 1990, but had little effect on soil properties measured in the fall.
Establishment of ‘Tifton 9’ Bahiagrass in Response to Planting Date and Seed Coat Removal
Authors: Gates Roger N. , Dewald Chester L.
Published: July 2010

Stands of ‘Tifton 9’, like those of other bahiagrasses (Paspalum notatum Flügge var. saurae Parodi), develop slowly. Our objectives were to determine seedling emergence and stand establishment responses to planting date and mechanical seed coat removal using greenhouse and field plantings. Seed dehulled by acceleration in an airstream to hit a metal plate (7.8 kg ha−1) or whole seed (11.2 kg ha−1) was planted at equivalent rates in five blocks of a randomized complete block design on seven biweekly planting dates from 9 March through 1 June in 1994 and 1995 at both a droughty upland site (Dothan loamy sand: fine‐loamy, siliceous, thermic Plinthic Kandiudults) and a lowland site (Alapaha sand: loamy, siliceous, thermic Arenic Plinthic Paleaquults) near Tifton, GA (31°26′ N, 83°35′ W), to observe emergence and establishment. Spring and fall plant counts and final stand ratings of percent bahiagrass occurrence were used to evaluate emergence and establishment. Emergence 7 d after greenhouse planting of dehulled seed (18.3%) was greater (P < 0.01) than whole seed (0.7%). Emergence at 28 d after planting was not different (36.2%) between seed treatments. Mean surface (0 to 50 mm) soil moisture content at the lowland site (58 g kg−1) was higher than the upland site (28 g kg−1). Seedling heights, measured in June 1994, spring seedling number in both years, and 1995 fall plant numbers were often higher with earlier planting date. No differences in final stand (% occurrence) could be attributed to planting date. Final stand ratings were greater (P < 0.05) at the lowland (84%) than at the upland site (79%), and greater (P < 0.05) for whole than for dehulled seed in 1994, but no differences were observed in 1995. Development of Tifton 9 bahiagrass stands at these Coastal Plain sites was slow, but relatively insensitive to differences in spring or early summer planting date. Dehulled seed emerged more rapidly, but this provided no sustained advantage in stand establishment in these environments.
An Integrated Approach to Managing Nitrogen on Dairy Farms: Evaluating Farm Performance Using the Dairy Nitrogen Planner
Authors: Dou Zhengxia , Lanyon Les E. , Ferguson James D. , Kohn Richard A. , Boston Raymond C. , Chalupa William
Published: July 2010

Nutrient flow in dairy farming involves animal and field components that are linked by transfers of crops and manure. Connections of the farm to the surrounding environment are created by inputs and outputs of feed, fertilizer, biological N2 fixation, animals and animal products, and nutrient losses to air and water. Because of these linkages among farm components and connections to the environment, an integrated system‐level approach would be useful to evaluate farm performance in terms of production efficiency and environmental protection goals. The purpose of this study was to evaluate dairy farm N flow and management by comparing farm performance data with reference values from the Dairy Nitrogen Planner (DNP), an integrated animal and field spreadsheet planning and evaluation tool. Performance data were from two Pennsylvania dairies: Farm 1,109 lactating Holstein cows (Bos taurus), with forages produced on 92‐ha crop land and supplemental feeds purchased as directed by nutritional services; Farm 2, 65 lactating cows, with nearly all feeds produced on the 111‐ha crop land and no forage quality analysis or ration formulation assistance. Farm performances on Farm 1 and 2, respectively, were (with the difference relative to the DNP projection): annual N input, 17 450 kg (−5%) and 10 670 kg (−10%); milk‐N output, 3880 kg (−8%) and 2790 kg (−0.4%); feed‐N intake, 20 200 kg (−2%) and 18 820 kg (+1%); and manure N for application, 8550 kg (−14%) and 10 200 kg (+11%). The differences between farm performance and DNP projections identified overall farm organization and crop management opportunities for improved farm system performance on Farm 1. Animal ration balancing was identified as a priority area for enhancement on Farm 2, with subsequent action to adopt the services of a professional nutritionist increasing milk production by 20% and decreasing manure N by 10%.
Inoculation and Nitrogen Affect Herbage and Symbiotic Properties of Annual Medicago Species
Authors: Zhu Yanping , Sheaffer Craig C. , Vance Carroll P. , Graham Peter H. , Russelle Michael P. , Montealegre C. M.
Published: July 2010

The interactive effects of Sinorhizobium inoculants and soil N status should affect the N contribution of annual medics (Medicago spp.) in cropping systems. We determined the effect of N and commercial medic inoculum on nodulation, dry matter, and N yield of annual medics and also determined Sinorhizobium strain occupancy in annual medic nodules. Field experiments were conducted on a sandy, mixed Udorthentic Haploboroll and on a fine‐loamy, mixed, mesic Typic Hapludalf. More than 75% of annual medic plants (except M. rugosa Desr.) were nodulated in the absence of commercial inoculum, and nodulation was due in part to a Sinorhizobium strain that frequently nodulates alfalfa (Medicago sativa L.). Among the five strains in the commercial medic inoculum, 102G3 and 102A13 had the greatest nodule occupancy. When no N was applied, inoculation improved the percentage of plants nodulated and nodule mass only in M. rugosa, compared with no inoculation, but inoculation increased herbage yields of spring‐seeded M. truncatula Gaertn. cv. Sephi, M. polymorpha L., and M. rugosa by about 60%, compared with no inoculation. Nitrogen addition reduced the nodule mass of all species when inoculum was applied, and N addition increased only the herbage dry matter yield of spring‐seeded M. scutellata (L.) Mill. when inoculum was applied. This suggests that a more effective inoculum could be developed for M. scutellata so that N would not limit herbage growth. Annual medics fixed from 40 to 80 kg N ha−1 if spring‐seeded and grown for 60. d, and from 20 to 50 kg N ha−1 if summer‐seeded and grown for 43 d.