bluuebunny/crossref_metadata_2025 huggingface dataset:
Yield Accumulation in Irrigated Sugarcane: I. Effect of Crop Age and Cultivar
Authors: Evensen Carl I. , Muchow Russell C. , El‐Swaify Samir A. , Osgood Robert V.
Published: July 2010

Because the duration of growth for commercial sugarcane (Saccharum spp. hybrids) production can vary from 9 to 36 mo, determining the optimum age at crop harvest is important to profitability. To account for variable climate across seasons and locations, there is a need to understand the physiology of yield accumulation and quantitatively describe the effects of crop age on productivity. Few field studies have been conducted to determine the factors responsible for yield variation in different cultivars of sugarcane at different crop ages, and the physiology of yield accumulation has rarely been examined on a dry matter basis with all yield components, including tops, millable stalk, trash, and roots. This paper compares above‐ and belowground biomass accumulation with crop age in two current cultivars grown in field experiments under drip irrigation in Hawaii from 1991 to 1993, and reanalyzes earlier experiments conducted in Hawaii in the 1930s and 1940s to examine historical changes in the pattern of yield accumulation in sugarcane. The key findings from this analysis are that (i) differences in yield accumulation during the first 12 mo of growth were not necessarily reflected in final yields at harvest at 18 to 24 mo; (ii) yield accumulation was less efficient in the second year of growth for current cultivars, but not necessarily so for older cultivars; (iii) belowground biomass decreased from 17% of total biomass at 6 mo to 11% of total biomass from 12 to 24 mo; (iv) there was no indication that older cultivars were less productive than current cultivars; and (v) yields rarely increased beyond 18 mo of age.
Soil Moisture and Larval Western Corn Rootworm Injury: Influence on Gas Exchange Parameters in Corn
Authors: Hou Xin , Meinke Lance J. , Arkebauer Timothy J.
Published: July 2010

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is an economically important pest of corn (Zea mays L.) in North America, but little is known about the physiological responses of corn to larval corn rootworm damage. This study was conducted to (i) characterize how larval corn rootworm feeding affects corn photosynthetic rate (Ps), stomatal conductance (gc), and intercellular CO2 concentration (Ci) and (ii) determine the interactive effects of larval injury and soil moisture on Ps, gc, and Ci. To address Objective 1, a greenhouse and a field experiment in randomized complete block design compared rootworm‐infested vs. noninfested Pioneer hybrid 3377 corn. Larval feeding had significant and transient effects on leaf Ps and gc (but not Ci) in both experiments. When the rootworm population was predominately second instar, leaf Ps and gc in infested corn were significantly less (P < 0.05) than in noninfested corn; at the end of the larval period, Ps and gc were not significantly different among rootworm treatments. Two greenhouse experiments addressed Objective 2. A factorial design with high and low moisture levels and rootworm‐infested and noninfested plants was used. In both experiments, soil moisture level interacted with larval injury to significantly (P < 0.05) affect leaf Ps and gc (but not Ci). Within 24 h after the two moisture regimes were established, Ps of the noninfested plants dramatically increased, while rates of rootworm‐infested plants did not change in plants that received supplemental water. Over 5 d, Ps rose in rootworm‐infested plants until rates equilibrated among rootworm treatments that were given supplemental water. These results suggest that irrigation of infested corn may not immediately reduce the stress caused by larval injury. A combination of factors (e.g., water uptake reduction, hormone synthesis in roots) may be involved in the injury‐plant response process.
Analysis of a Randomized Block Design with Unequal Subclass Numbers
Authors: Piepho Hans‐Peter
Published: July 2010

For some types of agricultural experiments, there are many observations per experimental unit; i.e., the subclass number is greater than one. In this article, the focus is on the randomized complete block design. Practitioners are often faced with unequal subclass numbers due to unpredicted experimental problems. The present paper discusses the statistical analysis of such unbalanced data, where subclass numbers vary independently of treatment variables and the response variable is not influenced by subclass number. In an example using the SAS statistical package to analyze data from a randomized complete block greenhouse experiment, an analysis of cell means compared favorably with a more elaborate Satterthwaite method. Monte Carlo simulations yielded similar results for both methods. It is concluded that, in practice, the cell means analysis is preferable for its simplicity.
Nitrogen Release from Surface‐Applied Cover Crop Residues: Evaluating the CERES‐N Submodel
Authors: Quemada Miguel , Cabrera Miguel L. , McCracken Daniel V.
Published: July 2010

Further improvement of residue decomposition models may help to optimize the use of N released from cover crop residues. CERES models are widely used to simulate crop‐soil systems and have a common subroutine that describes N dynamics (CERES‐N). In this work, we tested CERES‐N with results from a litterbag study over 120 d in which crimson clover (Trifolium incarnatum (L.), rye (Secale cereale( L.), wheat (Triticum aestivum( L.), and oat (Avena sativa L.) residues were allowed to decompose on the soil surface. The field data were used to (i) evaluate the original CERES‐N and a modification of CERES‐N that allows users to enter actual sizes for the carbohydrates, cellulose, and lignin pools and (ii) determine the best‐fitting rate constants for decomposition of the carbohydrates and cellulose pools in the original CERES‐N and in CERES‐N with user‐supplied pool sizes. CERES‐N with the original rate constants or with rate constants and parameters proposed by other workers either underestimated (root mean square error RMSE = 1.23 g N m−2) or overestimated (RMSE = 2.18 g N m−2) N remaining in the crop residues after 120 d of decomposition. CERES‐N with user‐supplied pool sizes improved the simulation of N remaining after 120 d (RMSE = 0.69 g N m−2), but the simulated values generally tended to overestimate the field data. The best‐fitting rate constants for carbohydrates and cellulose pools were 0.67 and 0.021 d−1, respectively, for the original CERES‐N (RMSE = 0.77 g N m−2), and 0.17 and 0.011 d−1 for CERES‐N with user‐supplied pool sizes (RMSE = 0.55 g N m−2). Future work should further evaluate these fitted rate constants under field conditions.
White Lupin Growth, Yield, and Yield Components in Eastern Canada: Influence of Management Factors
Authors: Faluyi M. A. , Zhang F. , Leibovitch S. , Smith D. L.
Published: July 2010

Management studies are required to assess the full potential of white lupin (Lupinus albus L.) as a grain crop for eastern Canada. A 2‐yr study to quantify the effects of management practices on morphology, yield, and yield components of two large‐seeded white lupin cultivars (Primorski and Ultra) was conducted at the E.A. Lods Agronomy Research Centre of McGill University in Quebec, Canada, on a fertile sandy loam soil and a well‐drained clay loam soil. Treatments included two planting dates, two row spacings (20 and 40 cm), and two cultivars, factorially combined on two soil types in 1991 and 1992. The weather was unusually cool and wet in 1992, while 1991 was more typical of the area. In both years, there were effects on plant growth, yield, and yield components due to soil types, sowing dates, row widths, and cultivars. In 1991, Ultra had 23 and 55% greater seed yield than Primorski on clay loam and sandy loam soils, respectively, whereas yields did not differ between the two cultivars in 1992. Early seeding resulted in greater yields than later seeding in both years, but this effect was larger in 1991 than 1992. Yields were higher when lupin was produced in narrower than wider rows; the effect was more pronounced on a clay loam than on a sandy loam soil. Interactions occurred between lupin cultivars and each of the three management factors (row width, seeding date, and soil type). Overall, an early seeding date in narrow rows is recommended for lupin production in short‐season areas.
Water Stress during Seed Filling and Leaf Senescence in Soybean
Authors: De Souza P. I. , Egli Dennis B. , Bruening William P.
Published: July 2010

Water stress during seed filling could reduce soybean [Glycine max (L.) Merr.] yield by accelerating leaf senescence and shortening the seed filling period. Greenhouse experiments were conducted to (i) evaluate the effect of water stress during seed fill on leaf senescence and (ii) determine the potential role of redistributed C and N in moderating the effect of water stress during seed fill. Soybean plants (‘McCall’, Exp. 1; ‘Elgin 87’, Exp. 2) were grown in soil‐filled pots. At the beginning of Growth Stage R6, two levels of water stress were imposed until maturity: daily waterings of 60% (moderate stress) and 30% (severe stress) of the water required to bring well‐watered pots to field capacity. Moisture stress reduced yield by reducing seed size (8–20%) in Exp. 1 and seed number (18%) and seed size (14–32%) in Exp. 2. Moisture stress accelerated leaf senescence, as shown by more rapid declines in leaf chlorophyll and N, and shortened the seed filling period in both experiments. In Exp. 2, a 50% depodding treatment was applied at the beginning of Growth Stage R6. Depodding delayed senescence and physiological maturity. Moisture stress accelerated leaf senescence and reduced seed size on the depodded plants, but the effect was less than on the nondepodded plants. Our results demonstrate that moisture stress during seed filling reduces yield by accelerating senescence and shortening the seed filling period. Increasing the source‐sink ratio may reduce the effect of moisture stress on seed size.
Lentil Green Manure as Fallow Replacement in the Semiarid Northern Great Plains
Authors: Pikul Joseph L. , Aase J. Kristian , Cochran Verlan L.
Published: July 2010

Green manures (GM) may offset inorganic N needs and improve soil quality. Study objectives were to determine effects of green manure on soil‐N fertility, water use, soil quality, and yield of spring wheat (Triticum aestivum L.). On two treatments, lentil (Lens culinaris Medikus cv. Indianhead) was green manured in a green manure‐spring wheat rotation. Lentil was killed by disking (GMMF) or chemicals (GMCF). Additional treatments were annually cropped wheat (AW) in a mechanical fallow (MF) or chemical fallow (CF) sequence. No inorganic N was used on GMMF and GMCF. Experiments were started in 1991 on a Williams loam (fine‐loamy, mixed Typic Argiboroll) near Culbertson, MT. Green‐manure treatments used 56 mm more water than fallow treatments when lentil was grown to lowerpod set. When lentil was killed at full bloom, there were no differences in water use among GM and fallow treatments. There were no differences among treatments in soil water at wheat planting. Wheat yield was 25% less on GM than on MF and CF. Soil NO3‐N (0–0.6 m) was 35% less on GM than MF and CF rotations. There were no differences in soil quality indicators of bulk density, organic C, pH, electrical conductivity, and deep NO3‐N (0.6–1.8 m) among treatments after two cycles of GM. Potentially mineralizable N was 66% greater on GM treatments than on fallow treatments. Short‐term results (5 yr) show that available N limited wheat production more than did soil water on the GM treatments. Soil improvement using green manures may require many additional cropping cycles.
ROOTEDGE: Software for Measuring Root Length from Desktop Scanner Images
Authors: Kaspar Thomas C. , Ewing Robert P.
Published: July 2010

One approach for measuring the length of roots washed from soil samples is to use a desktop scanner to acquire binary images and then use image analysis procedures to determine root length. Normally, this approach requires user‐adjusted exposure thresholding. The objectives of this study were to develop a procedure for obtaining binary images of root samples with a desktop scanner that does not require user‐adjusted exposure thresholding of each image and to test the performance of the newly developed ROOTEDGE program by using images containing single or multiple root segments of corn (Zea mays L.). ROOTEDGE was developed for measuring the length of digitized roots using the edge chord algorithm. It is insensitive to object orientation, has four image‐processing operations, and holds only seven lines of the image in memory. Visual comparisons of digitized images with actual root segments showed that root segments with diameters less than 0.15 mm were not being completely digitized by the image acquisition procedure and were fragmented in the images. The most complete root images were produced by using the highest available scanner resolution and the lowest scanner threshold level for exposure. Using the closing image‐processing operation in ROOTEDGE with a test coefficient of 1 also helped to join fragmented objects within images and improved the correlation of ROOTEDGE measurements to direct measurements. Ratios of ROOTEDGE length measurements to manual line‐intersection length measurements ranged from 0.98 to 0.88 for four corn root samples of different sizes. In general, the ROOTEDGE software and image acquisition system accurately measured corn root length without user‐adjusted exposure thresholding.
Variation among Soybean Cultivars in Dinitrogen Fixation Response to Drought
Authors: Serraj Rachid , Sinclair Thomas R.
Published: July 2010

Dinitrogen fixation in soybean [Glycine max (L.) Merr.] is especially sensitive to soil drying, and this trait can have important negative affects on yield. An exception to this general response has been the identification of ‘Jackson’ soybean as drought tolerant for N2 fixation. The objectives of this research were to examine the response in additional soybean cultivars of N2 fixation to soil drying under field conditions, and to determine if there is any link between the drought sensitivity among cultivars and the ureide levels in the plants. Two field experiments were conducted to further examine the genetic variation in the sensitivity of soybean cultivars for biomass and N accumulation rates in response to soil drying. Substantial variation among soybean lines was found, and the drought‐tolerance trait was demonstrated again in Jackson. Differences between cultivars in the response of N accumulation to drought stress were associated with differences in petiole ureide concentration found in well‐watered plants. An experiment was conducted in the greenhouse with eight soybean cultivars grown in pots and exposed to drought by soil dehydration over a 2‐wk period. Differences among cultivars in the sensitivity of N2‐fixation rates to soil drying found from measurements of acetylene reduction activity (ARA) in the greenhouse correlated with differences in N accumulation in the field (r2 = 0.86). The tolerance of N2 fixation to drought stress was associated (r2 = 0.84) with maximum ARA in response to changes in O2 concentration around nodules. Among the eight cultivars, there was a significant negative correlation (r2 = 0.73) between the drought tolerance of N2 fixation and ureide concentration in the xylem sap. Ureide levels might be an efficient way to screen large numbers of genotypes for N2‐fixation drought tolerance.
Establishment of Rhizoma Peanut: Interaction of Cultivar, Planting Date, and Location on Emergence and Rate of Cover
Authors: Williams M. J. , Kelly‐Begazo C. A. , Stanley R. L. , Quesenberry K. H. , Prine G. M.
Published: July 2010

Rhizoma perennial peanut (RPP), Arachis glabrata Benth., has high nutritive value, drought tolerance, and persistence; however, inconsistent establishment success and slow rate of coverage has limited the use of RPP in production systems. The objectives of this study were to determine the effects of planting date (February, April, June, August, and December), location (Brooksville, Gainesville, and Quincy, FL), and cultivar (Florigraze and Arbrook) on emergence (sprouts per square meter at 2 to 12 wk post planting) and rate of RPP cover (percent ground cover at 26, 52, 78, and 104 wk post planting). We also determined the relationship of sprout counts during the emergence period with rate of cover. Number of sprouts per square meter at 12 wk post planting ranged from 0 to >200 and, in most cases, the sprout counts obtained for April, June, August, and December planting dates were lower or equal to those from the February planting date, regardless of location or cultivar. Generally, Arbrook had higher numbers of sprouts per square meter at 12 wk post planting than Florigraze, but this did not translate into higher ground cover ratings at 26 wk. Number of sprouts per square meter was positively correlated with percent ground cover. The highest correlation coefficient (0.69) occurred for the relationship of sprouts per square meter at 12 wk post planting and ground cover at 26 wk post planting; correlations of responses declined from that point as stands aged. Rate of cover was also variable, taking between 26 and >104 wk post planting to reach >60% RPP ground cover. On average, February plantings achieved >60% RPP ground cover 26 wk earlier than any of the other planting dates. This study indicates that establishment times for RPP can be more variable than has been thought. The first criterion for deciding when to plant is the need for reliable soil moisture (from rainfall or irrigation) for 60 to 90 d post planting. Secondly, if there is more than one time of the year that meets this moisture requirement, then the planting date with the longest frostfree period after planting should be chosen.
Diversity, Stability, and Sustainable American Agriculture
Authors: Brummer E. Charles
Published: July 2010

If the great successes of American agriculture hide risks to match, what can be done to level out the risks, to reach stability, while preserving productivity? How does research contribute to the problem, or to its solution?
Evapotranspiration, Yield, and Water Use Efficiency of Corn Hybrids Differing in Maturity
Authors: Howell Terry A. , Tolk Judy A. , Schneider Arland D. , Evett Steven R.
Published: July 2010

Short‐season corn (Zea mays L.) hybrids may reduce irrigation requirements and permit earlier harvest. We measured and compared evapotranspiration (ET) of a short‐season (SS, Pioneer 3737) and full‐season (FS, Pioneer 3245) hybrid under full irrigation in 1994 at Bushland, TX, and examined differences in growth, yield, and water use efficiency (WUE). Both hybrids were planted the same day in contiguous 4‐ha fields (each field with a weighing lysimeter to measure ET directly), were irrigated simultaneously until the SS hybrid reached mid grain fill (R5 dent stage), and were managed for high productivity. Harvest was at the normal field‐dried grain water content of 136 g kg−1 for the region. Rainfall was 320 mm; 465 and 577 mm of irrigation was applied to the SS and FS hybrid fields, respectively. Seasonal ET was reduced with the SS hybrid (SS, 673 mm; FS, 802 mm), with the primary reduction after SS anthesis. Peak daily ET rates (some >10 mm d−1) were not affected by hybrid type. Grain yields (dry basis) declined from 1322 to 1130 g m−2, but grain water use efficiency (WUEg = grain yield/ET) was similar across hybrids: SS, 1.68 kg m−3; FS, 1.65 kg m−3. Dry matter (DM) was reduced by >390 g m−2 for the SS hybrid, but DM water use efficiency (WUEd = DM/ET) was identical for the two hybrids, at 3.02 kg m−3. The SS hybrid reached physiological maturity 12 d earlier than the FS hybrid and was harvested 11 d sooner. Leaf area index was >5.5 m−2 m−2 for the FS hybrid, but barely >4 m−2 m−2 for the SS hybrid. The WUEd, WUEg, and peak daily ET rates were not appreciably different for the two hybrids when fully irrigated, although seasonal ET was less with the SS hybrid. A shorter‐maturity hybrid can reduce ET and seasonal irrigation requirement, but it will not reduce the needed irrigation capacity (flow per unit area) by more than 5 to 10%, as that is largely dictated by the near‐maximum daily ET rate needed to avoid soil water deficits and a corresponding yield reduction. With prevailing regional pumping and production costs, the reduced production income with a SS hybrid would be more than six to eight times the saving in irrigation water cost, but this could be offset by higher grain marketing prices with an earlier harvest and by the opportunity for grazing income from a winter wheat (Triticum aestivum L.) double‐crop.
Forage and Nitrogen Yield of Barley—Pea and Oat—Pea Intercrops
Authors: Carr Patrick M. , Martin Glenn B. , Caton Joel S. , Poland W. W.
Published: July 2010

Barley (Hordeum vulgare L.) and oat (Avena sativa L.) have been intercropped with field pea [Pisum sativum subsp. sativum var. arvense (L.) Poir.] to increase forage yield and quality. Our objective was to evaluate the effects of two barley and two oat cultivars and seeding rates of cereal—pea intercrop on forage production, crude protein (CP) concentration, and N yield. A field experiment was conducted in 1993 and 1994 under dryland management in both fallowed and continuously cropped, no‐tillage environments. ‘Bowman’ and ‘Horsford’ barley, and ‘Dumont’ and ‘Magnum’ oat, were each sown at 93, 185, and 278 kernels m−2 with ‘Trapper’ pea at 40, 80, and 120 seeds m−2, in all possible rate combinations. The cereal cultivars also were sown alone at 185 kernels m−2. Cultivars developed for forage production (Horsford, Magnum) produced as much or more forage than cultivars developed for grain production (Bowman, Dumont) across sole‐crop and intercrop plots (P ≤ 0.05). Forage yield was unaffected by intercropping when the cereal crop was sown at the sole‐crop or greater rate. Less forage was produced by intercrops when the cereal component was sown at half the sole‐crop rate. Forage yield was not affected by the pea seeding rate, but CP concentration increased with increasing seeding rate of pea in three of four environment‐years. Forage N yield was unaffected by intercropping. These data indicate that the cereal component in barley—pea and oat—pea mixtures should be sown at a sole‐crop or greater seeding rate for maximum forage production. Forage CP concentration can be increased as the relative proportion of pea seed to cereal kernels sown in a mixture is increased, but forage N yield may not be affected, since the cereal component contributes more to yield than the pea component.
Plant Density Effects on Tropical Corn Forage Mass, Morphology, and Nutritive Value
Authors: Cuomo Greg J. , Redfearn Daren D. , Blouin David C.
Published: July 2010

Tropical corn (Zea mays L.) has potential as a silage crop in doublecrop systems with cool‐season annual grasses in the southeastern USA. In a 3‐yr study conducted in silt loam soils in southeast Louisiana, plots within stands of Pioneer hybrid X304C tropical corn planted at 89 000 plants ha−1 were thinned to achieve harvested plant densities of 44 830, 52 150, 58 130, 65 150, and 72 920, plants ha−1 to to determine the effect of plant density on total forage mass, plant morphology, and forage nutritive value of tropical corn. Total forage mass was greater at higher plant densities than at lower plant densities, but forage mass was not different among plant populations that exceeded 58 130 plants ha−1. Leaf concentration of dry matter did not differ among plant populations and averaged 300 g kg−1. The sum of stem and grain concentrations was similar among treatments and ranged from 622 to 637 g kg−1. Within the stem and grain components, grain concentration decreased and stem concentration increased in an almost one‐to‐one relationship as plant density increased. Forage nutritive value of tropical corn was similar among plant densities. In vitro true digestibility averaged 654 g kg−1 across all plant densities. Increasing forage mass, coupled with stable forage nutritive values, indicates that, until some factor limits production of high‐quality tropical corn silage, high plant densities are desirable. Under the environmental conditions of this experiment, it appears that plant densities of about 58 000 plants ha−1 are optimal.
Simulated Traffic on Turfgrass Topdressed with Crumb Rubber
Authors: Rogers John N. , Vanini J. Timothy , Crum James R.
Published: July 2010

Topdressing plays a vital role in turfgrass subjected to traffic. Sand is commonly used for topdressing; under suboptimal growing conditions, however, methods to maintain wear tolerance are limited. There has been recent interest in using crumb rubber from recycled tires as an amendment for turfgrass areas. A topdressing study was initiated in July 1993 to determine the effect of crumb rubber on turfgrass systems subjected to traffic. A factorial randomized complete block design with three replications was implemented with two crumb rubber particle sizes (large, 6.0–2.0 mm; small, 2.0–0.05 mm) and five topdressing rates (0.0, 17.1, 34.2, 44.1, and 88.2 t ha−1) on a 1‐yr‐old Kentucky bluegrass‐perennial ryegrass (Poa pratensis L.‐Lolium perenne L.) stand. In 1993 and 1994, 96 passes were made with a Brinkman traffic simulator. Surface hardness characteristics measured were peak deceleration, time to peak deceleration, and impact duration. The small crumb rubber size was more effective in increasing impact time periods than the large crumb rubber, but had no effect on peak deceleration values. Shear resistance values decreased by as much as 40% as crumb rubber volumes increased in 1993, but were increased by 20% in 1994 after rubber particles had settled to the soil surface. There was generally an increase in turf cover under traffic as crumb rubber rates increased above 34.1 t ha−1, and the small crumb rubber was more effective in 1993. Our results suggest that crumb rubber can alter surface characteristics and increase wear tolerance of turfgrass exposed to traffic.
Scales 2: Computer Program to Convert among Developmental Stage Scales for Corn and Small Grains
Authors: Harrell Dorothy M. , Wilhelm Wallace W. , McMaster Gregory S.
Published: July 2010

Producers and agronomists need crop developmental scales that are easy to use, universally accepted, and accurate. Development of such a scale requires correlation of stages among scales currently in use and correlation of developmental patterns among crops. A computer program for converting among staging systems is a useful tool in developing new staging systems with wider applicability. The BBCH scale (BASF‐Bayer‐Ciba‐Geigy‐Hoechst) has been proposed as a prototype of a universal scale. We have added the BBCH scale to our scale conversion program for wheat (Triticum aestivum L.) and developed a similar conversion program for corn (Zea mays L.), based on correlations reported in the literature. SCALES 2 provides a tool to translate among several widely used scales for corn and small‐grain development, and can be used to develop familiarity with the various scales.
Wheat Yields, Nitrogen Uptake, and Soil Moisture Following Winter Legume Cover Crop vs. Fallow
Authors: McGuire Andrew M. , Bryant Dennis C. , Denison R. Ford
Published: July 2010

Long‐term use of fallow in dryland wheat (Triticum aestivum L.) systems can increase erosion and decrease soil fertility. One possible solution is to grow a green manure crop during the fallow period. To evaluate the short‐term effects of substituting a winter legume green manure for fallow in a 2‐yr wheat rotation, a series of experiments were conducted in the Sacramento Valley of California from 1994 to 1996. Soil water content, inorganic soil N, and yield of fertilized wheat after fallow were compared with those of unfertilized wheat following a woollypod vetch‐field pea [Vicia villosa Roth subsp. varia (Host) Corb.; syn. V. dasycarpa Ten.‐Pisum sativum] green manure crop. Supplemental experiments (1995–1996) compared unfertilized wheat following (i) fallow with incorporation of legume biomass imported from another plot, (ii) growth and incorporation of green manure plus supplemental legume biomass from another plot, or (iii) growth of a legume crop with removal of aboveground biomass. Soil water content after a green manure crop was 6.6 cm less than after fallow in 1994 (to the 90‐cm depth), but only 1.5 cm less in 1995 (to 150 cm). During the wet winter of 1995–1996, fertilized wheat plots after fallow had higher inorganic soil‐N levels than unfertilized plots following a green manure crop, but wheat yields were similar. Where a green manure crop was grown and incorporated, there was no wheat yield response to additional legume biomass. Similarly, without a green manure crop, there was no yield difference between fertilized plots receiving 112 vs. 28 kg N ha−1. Results could be different in drier years or in soils with lower N fertility, but the data indicate that possible long‐term yield benefits of green manuring are not necessarily preceded by lower short‐term yields.
Recycling in situ of Legume‐Fixed and Soil Nitrogen in Tropical Lowland Rice
Authors: George Thomas , Buresh Roland J. , Ladha Jagdish K. , Punzalan Gloria
Published: July 2010

In tropical rice lowlands, vegetation during the dry‐to‐wet season transition (DTW) facilitates in situ recycling of N from soil or legume biological nitrogen fixation (BNF) to wet‐season flooded rice. As little is known, we examined the fates of soil N and BNF N in DTW vegetation in a 2‐yr study on a Philippine Tropudalf using 15N‐labeled residues produced and soil‐incorporated in situ. During DTW, Sesbania rostrata (Bremek. & Oberm.), mungbean [Vigna radiata (L.) R. Wilczek var. radiata], weeds, and a weed‐free fallow were subplots in dry‐season main plots of weedy, weed‐free, and frequently tilled fallows. Rice yield and N uptake were not influenced by dry‐season fallows, which did influence soil N and BNF N in DTW vegetation and, therefore, the amount of soil N lost, removed in a product or recycled. Build‐up and decline of soil NH4−N occurred within 5 wk of residue incorporation, before significant N uptake by rice. Rice yield and N uptake responded to greater recycled DTW N; N uptake averaged 103 kg ha−1 with 208 kg S. rostrata N ha−1, 79 kg ha−1 with 62 kg mungbean N ha−1, 61 kg ha−1 with 41 kg weed N ha−1, and 44 kg ha−1 with no residue N. Nitrogen‐15 estimates of N recovery by rice (20% of S. rostrata N, 27% of mungbean N, 16% of weed N) were lower than the actual increase in rice N uptake due to residues. High proportions of residue N remained in soil, but N loss of 32% was estimated for S. rostrata N. As green manure (GM) N is ineffective beyond the first few weeks of incorporation, incorporating much legume N to flooded rice wastes valuable BNF N. Unmet rice N demand beyond early crop stage is better supplied with fertilizer N synchronized with rice N demand. A mixture of native weeds and GM legume is likely to prevent build‐up of soil NO∐3−N and allow BNF while limiting total N accumulation in the DTW vegetation for use as GM.
Management Studies on Seed Production of Turf‐Type Tall Fescue: II. Seed Yield Components
Authors: Young William C. , Youngberg Harold W. , Silberstein Thomas B.
Published: July 2010

Information on how management affects seed yield components of turf‐type tall fescue (Festuca arundinacea Schreber) cultivars is needed to improve cultural practices for seed production. We tested factorial combinations of two post‐harvest residue managements (flailchopping or burning the stubble), two row spacing (0.3 and 0.6 m), three spring‐applied N rates (100, 145, and 190 kg ha−1), and three N application timings (double‐ridge, spikelet initiation, and equally split between the two) on seed yield components of turf‐type cultivars Falcon, Rebel, and Bonanza, and the forage cultivar Fawn. Seed yields of all cultivars were closely correlated with the number of seeds produced per unit area (m2), but yields were weakly and negatively correlated with weight per seed. Compared with flail‐chopping, burning the residue increased the numbers of fertile tillers, floret sites, and seeds per unit area in all cultivars. The number of seeds per unit area was not affected by row spacing in Fawn and Bonanza, but was increased at 0.3‐m row spacing in Falcon when the residue was burned, and was greater at 0.6‐m in Rebel when the residue was flail‐chopped. Increasing N rate above 100 kg ha‐1 decreased floret site utilization and seeds per unit area in Fawn, but did not affect these components in Falcon and Rebel. Seeds per unit area in Bonanza was the greatest at 145 kg N ha‐1. For all cultivars, N application timing had little effect on seeds per unit area. We conclude that management practices for the turf‐type cultivars should focus on maintaining a high number of fertile tillers throughout the stand life by burning post‐harvest residue. Using narrower row spacings for early‐ and mid‐maturing turf‐type cultivars also could increase the number of fertile tillers per unit area when the post‐harvest residue is burned. The optimum spring‐applied N rate for seed production is apparently greater for the late‐maturing turf types than for forage cultivars.
Cover Crop Root Distribution and Its Effects on Soil Nitrogen Cycling
Authors: Sainju Upendra M. , Singh Bharat P. , Whitehead Wayne F.
Published: July 2010

Nitrate N in the soil is susceptible to leaching with fall and winter precipitation and can pollute groundwater. Winter cover crops to scavenge residual NO‐3 through root extension are a possible solution. A 2‐yr field study was conducted on a Greenville fsl (fine, kaolinitic, thermic Rhodic Kandiudults) in central Georgia to determine root distribution of legume and nonlegume winter cover crops and their ability to absorb soil NO‐3 and accumulate it in aboveground biomass. Cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), and crimson clover (Trifolium incarnatum L.) were planted in a prepared seedbed in the fall and accumulated biomass was incorporated into the soil in the spring. Seasonal variations in root distribution were measured by minirhizotron and soil separation methods. Soil mineral N concentration and aboveground biomass yield and N uptake were determined at regular intervals during the growing season. Total minirhizotron root count (MRC; no. roots cm−2 soil profile) at the 1‐ to 50‐cm soil depth increased at the rate of 0.01 roots cm−2 d−1 in hairy vetch in the fall to 0.38 roots cm−2 d−1 in crimson clover in the spring, as temperature increased. Roots were well distributed to the 50‐cm soil depth. Compared with the other cover crops, rye had significantly greater total MRC from Dec. 1996 to Feb. 1997 and total root length density (RLD; cm root length cm−3 soil) at the 0‐ to 30‐cm depth from Nov. 1995 to Apr. 1996 and in Jan. 1997, and the subsequent NO‐3 inorganic N concentration in the soil was lower and aboveground biomass yield was greater. MRC was positively correlated with RLD in Nov. 1995, Apr. 1996, and Jan. 1997. A significant positive correlation was observed between MRC and aboveground biomass yield or N uptake (r = 0.52 to 0.68, P ≤ 0.05) and a negative correlation between MRC and soil NO‐3 concentration (r = ‐0.51 to ‐0.55, P ≤ 0.05) early in the growing season. Rye had the greatest root density and aboveground biomass, and scavenged more soil NO‐3 early in the growing season. Nonlegume cover crops, such as rye, may be more effective in reducing residual NO‐3 and potential leaching of NO‐3 from the soil early in the growing season than are legume cover crops, such as hairy vetch or crimson clover.
Rotation and Fertilization Effects on Corn and Soybean Yields and Soybean Cyst Nematode Populations in a No‐Tillage System
Authors: Howard Donald D. , Chambers A. Y. , Lessman Gary M.
Published: July 2010

Rotations have long been used to improve crop yields. No‐tillage production acreage is increasing, and production information on rotation effects on yields and soybean cyst nematode populations is needed for this system. Field experiments were initiated in 1985 and continued through 1992 to evaluate P‐K fertilization effects on yield of a corn‐soybean [Zea mays L.‐Glycine max (L.) Merr.] rotation and on populations of soybean cyst nematode (Heterodera glycines Ichinohe) (SCN). The research was conducted on a Loring silt loam soil (a fine‐silty, mixed, active, thermic Oxyaquic Fragiudalf), using no‐tillage management. The experimental design was a split‐plot for corn evaluation and split‐split‐plot for soybean evaluation. Individual treatments were replicated five times. Main plots were broadcast P‐K rates of 0–0, 15–28, 29–56, 44–84, and 59–112 kg ha−1. The split‐plots were continuous corn, continuous soybean, a corn‐soybean rotation, and a soybean‐corn rotation. The split‐split‐plots were two soybean cultivars possessing different levels of SCN resistance. Yields of both crops were increased by the fertilization. In this study, corn yields were increased 14% and soybean yields increased 11% with the rotation. Rotating the two cultivars produced similar yields and nonrotated yields of resistant TN 4‐86 were higher than susceptible Essex, indicating an effect of SCN. The primary benefit of corn in the rotation was to reduce SCN populations. However, within Essex rotations the SCN population recovery was rapid, while populations remained relatively low in the TN 4‐86 rotations. The SCN populations were greater when rotations were fertilized with the two lowest P‐K rates, compared with populations within the unfertilized check and the highest P‐K rate. Soybean producers should consider a no‐tillage system of rotating corn with SCN‐resistant soybean cultivars, fertilized at high P and K rates for yield improvement and reduced SCN populations.
Changes in Soil Chemical Properties Resulting from Organic and Low‐Input Farming Practices
Authors: Clark M. Sean , Horwath William R. , Shennan Carol , Scow Kate M.
Published: July 2010

Soil chemical properties during the transition from conventional to organic and low‐input farming practices were studied over 8 yr in California's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four farming systems differing in crop rotation and external inputs were established on land previously managed conventionally. Fertility in the organic system depended on animal manure applications and winter cover crops; the two conventional systems received synthetic fertilizer inputs; the low‐input system used cover crops and animal manure during the first 3 yr and cover crops and synthetic fertilizer for the remaining 5 yr. At 4 and 8 yr after establishment, most changes in soil chemical properties were consistent with predictions based on nutrient budgets. Inputs of C, P, K, Ca, and Mg were higher in the organic and low‐input systems as a result of manure applications and cover crop incorporations. After 4 yr, soils in the organic and low‐input systems had higher soil organic C, soluble P, exchangeable K, and pH. Ceasing manure applications in the low‐input system in Year 4 resulted in declining levels of organic C, soluble P, and exchangeable K. Crop rotation (the presence or absence of corn) also had a significant effect on organic C levels. Differences in total N appeared to be related in part to inputs, but perhaps also to differing efficiency of the farming systems at storing excess N inputs: the low‐input system appeared to be most efficient, and the conventional systems were least efficient. Electrical conductivity (EC), soluble Ca, and soluble Mg levels were tightly linked but not consistently different among treatments. Relatively stable EC levels in the organic system indicate that animal manures did not increase salinity. Overall, our findings indicate that organic and lowinput farming in the Sacramento Valley result in small but important increases in soil organic C and larger pools of stored nutrients, which are critical for long‐term fertility maintenance.
Modeling Freezing Injury in Alfalfa to Calculate Forage Yield: I. Model Development and Sensitivity Analysis
Authors: Kanneganti V. Rao , Rotz C. Alan , Walgenbach Richard P.
Published: July 2010

Freezing injury can cause extensive yield loss in alfalfa (Medicago sativa L.) exposed to severe winters in cold climates. Existing simulation models for alfalfa either do not account for freezing injury effects or do not differentiate cultivars for their varying response to freezing stress and subsequent effects on crop productivity. The objective of this project was to incorporate cultivar‐specific effects of freezing injury on forage dry matter (DM) yield into an existing alfalfa growth model to calculate annual forage yield during the life of an alfalfa crop. Numerical functions of cold tolerance, fall dormancy, and freezing injury were developed and integrated with the growth processes in the ALSIM 1 (Level 2) alfalfa model. The new model, ALFACOLD, requires input of: daily solar irradiance, maximum and minimum air temperature, and precipitation; latitude; dates of harvest; cultivar's fall growth score (FGS); initial plant density; and maximum plant‐available water in the root zone. The plant components modeled were leaf, stem, buds, and total nonstructural carbohydrates accumulated in the crown and root tissue. The model integrates the effects of soil moisture deficit, temperature, solar irradiance, and plant density on alfalfa growth, and the effects of subzero (°C) temperature on freezing injury and associated yield loss. Sensitivity of calculated forage DM yield to a ±25% change in selected model parameters was measured in cultivars of FGS 2, 3, and 4 during three production years of a 4‐yr alfalfa crop. The model did not simulate growth during a seeding year. A cultivar's rate of cold hardening and lowest temperature tolerance during autumn and winter influenced forage yield more than did the rate of dehardening in the spring. Field validation of ALFACOLD calculations of forage yield is presented in a companion paper.
Rhizoma Peanut Responses to Harvest Frequency and Nitrogen Fertilization on Louisiana Coastal Plain Soils
Authors: Venuto Brad C. , Redfearn Daren D. , Pitman W. D.
Published: July 2010

Despite limitations in stand establishment, rhizoma peanut (Arachis glabrata Benth.) is the only sustainable, productive, high‐quality, perennial, warm‐season legume available for the Coastal Plain of the lower Gulf Coast Region. Management to enhance productivity could increase acceptance of this relatively unexploited forage. Yield responses of rhizoma peanut to harvest frequency and N fertilization on Louisiana Coastal Plain soils were evaluated. Nitrogen rates of 0, 85, and 170 kg ha−1 were applied to a Dexter loam soil (Ultic Hapludalfs) in a greenhouse experiment. At three field locations, N rates were 0, 110, and 220 kg ha−1 and harvest frequencies were 30 and 60 d. Soils were the Dexter loam, Tangi silt loam (Typic Fragiudults), and Bowie fine sandy loam (Plinthic Paleudults). In the greenhouse, N accumulated in herbage (30 g kg−1 with 170 kg N ha−1 vs. 20 g kg−1 for the control) with a subsequent linear yield increase. In the field, the only responses to N fertilizer were small increases in N concentration of rhizomes plus stubble. Interactions of harvest frequency and location on herbage yield indicated effects of weather. This effect is illustrated by the 790 kg ha−1 advantage of the 30‐d harvest frequency on the Tangi silt loam in May–June vs. the 1930 kg ha−1 advantage of the 60‐d harvest frequency on the Bowie fine sandy loam in July–August. Thus, on the Louisiana Coastal Plain, yield of rhizoma peanut is not likely to be increased by N fertilization, and harvest frequency or length of regrowth period is not a reliable determinant of yield.
Soil Nitrate Accumulation and Corn Response to Preceding Small‐Grain Fertilization and Cover Crops
Authors: Vyn Tony J. , Janovicek Ken J. , Miller Murray H. , Beauchamp Eric G.
Published: July 2010

Potential benefits associated with establishing cover crops, such as reduced NO3 leaching risk and lower fertilizer N requirements for succeeding crops, will be fully realized only when the cover crop N contribution is accurately accounted for and availability is synchronous with succeeding crop N demands. The objectives of this study were to evaluate spring soil NO3−N accumulation patterns and N availability to corn (Zea mays L.) following annual ryegrass (Lolium multiflorum L.), oilseed radish [Raphanus sativus (L.) var. oleiferus (Stokes) Metzg.], red clover (Trifolium pratense L.), and no cover crop established after either winter wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.). The wheat and barley were produced with 0.5, 1.0, and 2.0 times the amount of recommended N fertilizer. Six field trials were conducted on well‐drained Typic Hapludalf soils in southwestern Ontario intermittently from 1989 to 1995. Corn was produced using a spring mulch‐till system with only 10 kg ha−1 of fertilizer N, which was applied as part of the P starter fertilizer. Applying more fertilizer N to the previous year's small‐grain crop rarely increased spring soil NO3−N concentrations or corn yields. Soil NO3−N concentration increases between the May and June sample dates following annual ryegrass and oilseed radish did not differ substantially from where a cover crop had not been established; following red clover, however, NO3−N increases were always at least 2.8 times greater than after no cover crop. Average aboveground corn biomass N at anthesis following annual ryegrass was 25.6 kg ha−1 less than when no cover crop was grown, whereas following red clover it was 40.4 kg ha−1 greater than with no cover crop. Corn yields were consistently the highest following red clover and often the lowest following annual ryegrass; yield response was positively correlated with June soil NO3−N concentrations (r = 0.61‐0.93). These results suggest that N availability to succeeding corn differs among the cover crop treatments evaluated in the order red clover > oilseed radish ≥ no cover crop > annual ryegrass.
Ammoniacal Nutrition of Transplanted Rice Fertilized with Large Urea Granules
Authors: Gaudin Remi , Dupuy Jacques
Published: July 2010

With deep placement of large urea granules in wetland rice (Oryza sativa L.) cultivation, N is protected from various loss mechanisms and quite well recovered by plants. The objective of this study, which was based on soil solution measurements, was to examine the relation between the localized NH3−rich area deriving from one granule and the surrounding plants. The influence of rice on the ammoniacal N was examined in terms of a model of diffusion describing the time course of the ammoniacal N concentration. Treatments were granule mass (1, 2, 3, and 4 g). Since greater amounts of NH3 are expected for larger granules, we asked whether this would hinder N consumption by the plant, and thus delay disappearance of the ammoniacal N from the soil. The soil solution was sampled with probes buried close to the granules. Urea was quickly hydrolyzed in the soil: 78 to 91% of the reaction was performed within 4 d and 95 to 98% within 13 d. As early as 4 d, the ammoniacal N generated was 0.313 mol dm−3 for 2‐g granules, with a diffusion coefficient for NH3 of 0.998 cm2 d−1 (equivalent to an instantaneous point source of NH3). In the field, diffusion drove the time course of NH3 until 10 mmol dm−3, a level attained earlier in the lower‐mass treatments (1 and 2 g) than in the 3‐ and 4‐g treatments. Thereafter, the patterns of NH3 disappearance changed: the lower‐mass treatments displayed a faster evolution than the larger treatments. This change indicates a different speed in the consumption of ammoniacal N, possibly in relation with the vegetative or reproductive stage of the plant, throughout the carbon investment into NH3 assimilation. The granule‐rice system is proposed as a model for research on source‐sink relationship at the whole‐plant level.