bluuebunny/crossref_metadata_2025 huggingface dataset:
Bradyrhizobium Inoculation and Nitrogen Fertilizer Effects on Seed Yield and Protein of White Lupin
Authors: Ayisi K. K. , Putnam D. H. , Vance C. P. , Graham P. H.
Published: July 2010

Variation in seed yield and protein levels of sweet white lupin (Lupinus albus L. cv. Ultra) in the North Central USA has limited production of the crop in this region. Poor N nutrition from biological or exogenous sources may be one of the causes of this variation. Studies were conducted under irrigation in 1988, 1989, and 1990 at Becker, MN, on a Hubbard loamy sand (sandy mixed udorthentic haploborolls) to examine the impact of Bradyrhizobium inoculation and N fertilizer on lupin seed yield, protein concentration, and yield components. Bradyrhizobium sp. (Lupinus) strains (WU425 and 96B15) were compared separately with non‐inoculated lupin controls in 1988 and then in combination in a 1:1 cell ratio in 1989 and 1990 at four concentrations of N fertilizer (0, 56, 112, 168 kg N ha−1). There were no significant differences in seed yield or protein between the two strains in 1988 but there was a trend for higher yield with WU425. Seed yield of inoculated plots was increased by an average of 51% in 1988 and two to five fold in 1989 and 1990, respectively, compared with noninoculated controls. Yield increases were due to changes in pod number or seed weight, depending upon the year of evaluation. Inoculation resulted in seed protein increases 28 to 45% greater than non‐inoculated controls at zero N. Symbiotic N2‐fixation by the difference method contributed 63 to 85% of seed N but these amounts decreased with addition of N fertilizer. Nitrogen fertilizer did not significantly increase seed yield, protein content, or protein yield of inoculated plants and seed yield of inoculated plants at zero N was always greater than that of well fertilized non‐inoculated plants. These results indicate the importance of Bradyrhizobium symbiosis in white lupin for both maximum seed yield and seed protein. Addition of N fertilizer to effectively nodulated lupin offered no advantage for either seed yield or protein.
Optimal Concentrations of Nitrate in Cornstalks at Maturity
Authors: Binford G. D. , Blackmer A. M. , Meese B. G.
Published: July 2010

The concentration of NO−3 in the lower portion of cornstalks at physiological maturity has been proposed as the basis for evaluating the N status of corn (Zea mays L.). Here we refine estimates of the optimal range in NO−3 concentrations for this test by using relevant economic scenarios that include 900 plot‐years of new data as well as 450 plot‐years reported earlier. The results showed that rainfall had little effect on concentrations of NO−3 identified as being optimal. However, calculations showed that optimal concentrations of NO−3 in stalks were influenced by prices of corn and fertilizer. For prices that have prevailed in the Corn Belt during the past decade, an optimal range of 0.7 to 2.0 g NO−3‐N kg−1 was shown to be more appropriate than the range originally reported. When this optimal range is used, the tissue test can be used to identify deficiencies of N as well as excesses of N. Overall, the results show that the end‐of‐season cornstalk test deserves attention as a tool for providing feedback that can be used to compare and refine systems for making N fertilizer recommendations.
Autumn Sward Suppression and Insect Control Effects on Late‐Winter No‐Till Establishment of Ladino Clover
Authors: Zarnstorff M.E. , Chamblee D.S. , Mueller J.P. , Campbell M.V.
Published: July 2010

Ladino clover (Trifolium repens L.) has traditionally been established in the autumn in the southeastern USA. Grass suppression and insect control have proven beneficial for successful autumn no‐till establishment. Winter planting offers an alternative, yet little is known about late winter grass suppression and insect or mollusk control. Herbicide applied at planting in late winter usually failed to suppress or kill cool‐season grasses. Field studies were conducted to evaluate (i) the influence of fall suppression or kill with paraquat (1,1'‐dimethyl‐4‐4' bipyridinium ion) of the tall fescue (Festuca arundinacea Schreb.) sward on late‐winter (February or March) no‐till establishment of ladino clover, (ii) establishment by drilling versus surface planting and (iii) the influence of suppression of insect and/or mollusk populations on the late‐winter no‐till establishment of ladino clover into tall fescue. Initial late winter no‐till clover densities were 30% greater for the March as compared to February planting (three experiment average). Drill planting of clover resulted in 2.1 times greater initial clover density (four experiment average) and 1.9 times more clover yield than surface planting (three experiment average). Application of paraquat to tall fescue in bands (13 cm) in mid‐October resulted in essentially complete grass kill with the bands. Neither autumn grass suppression nor the use of insecticide or molluscicide altered clover density or stand. Late‐winter, no‐till establishment provides an alternative to fall establishment. Our results indicate that fall chemical suppression of grass swards is not necessary for successful late‐winter establishment of ladino clover.
Relative Nitrogen Utilization by Legume Cover Crop Species at Three Soil Temperatures
Authors: Power J. F. , Zachariassen J. A.
Published: July 2010

When selecting a legume cover crop, one should know relative N‐fixing and N uptake capabilities, as well as growth and water use characteristics, to identify the species best adapted to the growth period and soil temperatures (season) during which the cover is crop grown. We provide information on these characteristics for eight inoculated legume species at soil temperatures of 10, 20, and 30 °C. Plants were grown in constant‐temperature water baths in a greenhouse for 105 d after establishment in 1.1 kg of Alliance silt loam (fine silty, mixed, mesic, Aridic Argiustoll) per pot. Plant samples were taken every 21 d for determinations of dry weight, total N uptake, and N2 fixed (isotope dilution method). Water use was measured daily by weighing. Total N uptake and N2 fixation were usually greatest for large‐seeded annual species during the first 42 to 63 d of the experiment. At 10 °C total N uptake and N2 fixation were greatest for hairy vetch (HV), Vicia villosa Roth and faba bean (FB), Vicia faba L. At later sampling dates, N uptake and fixation for white clover (WC), Trifolium repens L., was also relatively high. At 20 °C, soybean (SB), [Glycine max (L.) Merr.] exhibited outstanding growth and N uptake throughout the 105 d. For the first 42 d, FB performance also was superior to other species. At 30 °C, N uptake and fixation by SB was more than double that of any other species at all sampling dates. Quantity of N2 fixed per unit water used was greatest at 10 °C for WC, followed closely by HV and field pea (FP) Pisum sativum L.; at 20 °C, SB followed by WC and lespedeza (LD), Lespedeza stipulacea Maxim.; and at 30 °C, LD followed by SB. Our results suggest that under many situations (early spring) some grain legumes, such as and FB, may be a better cover crop than many species commonly used.
Field Response of Maize to a VAM Fungus and Water Management
Authors: Sylvia D. M. , Hammond L. C. , Bennett J. M. , Haas J. H. , Linda S. B.
Published: July 2010

Mycorrhizae improve plant nutrient uptake and are known to affect the water relations of plants grown in growth chambers and greenhouses. This paper summarizes a 3‐yr field study that tested the effects of mycorrhizae and water management on the growth and grain yield of maize (Zea mays L.). In each year, two inoculation treatments (inoculated or not with Glomus etunicatum Becker and Gerdemann) and three water‐management treatments (fully irrigated, moderate stress, and severe stress) were applied to fumigated and fertilized Millhopper fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult). Inoculum was placed in a furrow 10 cm deep at an average rate of 1500 propagules per meter of row. Six to 7 wk after planting, colonization ranged from 0 to 6% of total root length on noninoculated plants and from 10 to 61% on inoculated plants. Twelve to 13 wk after planting, colonization ranged from 2 to 30% on noninoculated plants and from 21 to 56% on inoculated plants. Water stress had little effect on root colonization. By 52 d after planting, one more leaf had appeared and one additional leaf had formed a collar on inoculated plants. Inoculation increased the concentrations of P and Cu in both shoots and grain on all measurement dates. Overall, grain yields (0.306) and total above‐ground biomass yields (0.458 Mg ha‐1 cm‐1 of water) increased linearly with irrigation. A positive response to mycorrhizal inoculation was constant across irrigation levels (0.802 for grain and 1.170 Mg ha−1 for biomass). Therefore, the proportional response of maize to inoculation with G. etunicatum increased with increasing drought stress.
Corn–Soybean Rotation Effects on Soil Water Depletion
Authors: Copeland P. J. , Allmaras R. R. , Crookston R. K. , Nelson W. W.
Published: July 2010

The positive yield effect of crop rotation may be linked to enhanced water uptake and associated efficient use. We hypothesized that a crop grown in rotation might deplete soil water more than the same crop grown under monoculture because some negative factor associated with monoculture was alleviated. Water use efficiency (WUE) might also be improved by rotation. The objective of our study was to determine whether altered water uptake or altered WUE was associated with the yield increase observed when corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are rotated. A long‐term corn‐soybean rotation experiment was monitored in 1987 and 1988 to determine seasonal soil water status to 1.50m. Corn and soybean sequences monitored were: monoculture, first‐year crop following 5 yrs of the other crop, second‐year crop following 5 yrs of the other crop, and an annual alteration of the two crops. Compared with monoculture, yield was increased up to 30% when corn followed soybean and up to 11% when soybean followed corn. Average soil water depletion during the season by first‐year corn was 16 mm greater than by continuous corn. The WUE in corn was related to cropping sequence at a moderate level of significance (p = 0.14). Seasonal soil water depletion by soybean was not changed by cropping sequence but overall WUE by first‐year soybean was higher than by continuous soybean (p = 0.05). When there was a period with only sparse rainfall in 1988, corn had a greater water depletion than soybean and also a deeper zone of depletion. Both crops exhibited a greater water depletion when rotated. Frequent rainfall in 1987 sufficient to wet the soil below 0.30 m obliterated patterns of depleted soil water. Increased water use observed in first‐year corn and increased WUE observed in first‐year soybean (compared to monoculture) in both years suggest that rotation allows these crops to increase root surface or root activity and hence to improve grain yield.
Compatibility of Kentucky Bluegrass and Perennial Ryegrass with Tall Fescue in Transition Zone Turfgrass Mixtures
Authors: Hunt K. L. , Dunn J. H.
Published: July 2010

Use of turf‐type tall fescue (TF), Festuca arundinacea Schreb., in mixture with Kentucky bluegrass (KB), Poa pratensis L., and, or perennial ryegrass (PR), Lolium perenne L., for sports turf may be advantageous because of genetic diversity and improved tolerance to pests and environmental stresses compared to TF in monoculture. The compatibility of TF in mixture with KB and PR, and TF in monoculture was evaluated over a 5‐yr period. Cultural treatments studied were 16 and 22‐mm mowing heights and 75 and 150 kg N ha‐1yr‐1 fall‐applied and 175 kg N ha−1yr‐1 spring‐fall applied N. Botanical composition and turfgrass cover were measured annually in June, 1985 to 1989, with an optical point quadrat. Visual quality ratings were taken monthly during the growing season. In the TF‐PR mixture, TF lacked competitiveness and had decreased from 51% the first year to 11% of the plant population 5 yr after planting. Tall fescue declined from 42% the first year to comprise 9% of the TF‐KB‐PR mixture after 5 yr. In the TF‐KB mixture, TF had an initial 1 yr decline of 60 to 44%, then remained competitive with KB and at 5 yr comprised 44% of the turf compared with 47% KB. The TF‐KB mixture and TF monoculture generally received higher quality ratings compared to the TF‐PR and TF‐KB‐PR mixtures starting in August 1988 and through completion of the study. Nitrogen and cutting height had little effect on botanical composition, and had occasional minor effects on turfgrass quality. These results show that selected, blended TF cultivars under non‐irrigated conditions can adapt to close mowing and remain competitive in mixture with selected blended KB cultivars over several years.
Skip‐Row and Equidistant‐Row Barley with Nitrogen Placement: Yield, Nitrogen Uptake, and Root Density
Authors: Sharratt B. S. , Cochran V. L.
Published: July 2010

Small grain management strategies are sought in the subarctic that improve the plant growing environment and maximize production. This study assessed whether seed‐row configuration and N fertilizer placement could alter growth and yield of barley (Hordeum vulgare L.) in the subarctic. Row spacing and N placement treatments established at Fairbanks, AK, during 1987 through 1989 consisted of equidistant‐row planting (0.18‐m equidistant seed rows) with N banded between alternate rows or broadcast and incorporated, and skip‐row planting (skipping every third row of equidistant rows) with N banded between the two closely spaced rows or broadcast and incorporated. Plant characteristics evaluated included tiller and head density, straw and grain yield, N uptake, leaf area, and root length density. Soil core samples were extracted to approximately 1 m in the mid‐interrow position near anthesis to determine root length density by the line intersect method. Tiller density was the primary yield component differing among treatments. Equidistant‐row barley had more tillers which resulted in a higher head density, 40% higher leaf area, and higher grain and straw yields than skip‐row barley. Rooting in the top 0.1 m of soil was more proliferous where N fertilizer was banded rather than broadcast, but total N uptake was not different among treatments. This study indicated that growth and yield of barley in the subarctic were favored by equidistant‐row planting with either banded or broadcast N applications.
The Effect of Citrate and pH on Zinc Uptake by Wheat
Authors: Chairidchai P. , Ritchie G. S. P.
Published: July 2010

Zinc uptake by plants may be influenced by its reaction with organic ligands in the rhizosphere. Therefore, four experiments were conducted to examine the effects of an organic ligand (citrate) and pH on the uptake of Zn by wheat (Triticum aestivum L. emend. Theil). Plants were grown for 21 to 28 d in a nutrient solution (containing 0–0.05 μmol L−1 Zn) in a temperature controlled tank, either in the absence or presence of citrate and at constant or variable pH (3.7–7.1). Dry matter weights of plant parts and Zn content in the shoots were determined. The activities of Zn in the nutrient solution were estimated. Shoot dry matter of the wheat plants in each experiment correlated well with either ZnT/[H+] or Σ(moles Zn1charge)/[H+] (ZnT = total Zn, Zn1 = each zinc species). Both parameters could explain the relative shoot dry matter of the plants from all experiments in one equation (y = A + BE−cx; r2 = 0.79 and 0.77, respectively). In the absence of citrate, shoot dry matter as well as Zn content increased with increasing pH and increasing total Zn concentrations in solution. In the presence of citrate, the shoot dry matter of wheat plants that were grown in nutrient solution with constant pH increased with the total Zn concentrations. However, the effect of the total Zn concentrations in the solution containing citrate with variable pH were less important than the effect of pH.
Parameterized Model of Gramineous Crop Growth: II. Within‐Season Simulation Calibration
Authors: Maas Stephan J.
Published: July 2010

The accuracy of parameterized crop growth models is dependent on obtaining the proper parameter values that control the response of the model to environmental conditions. In this study, a method is described for objectively evaluating model parameters based on observations of crop growth obtained during the growing season. An iterative numerical procedure is used to systematically manipulate the values of selected parameters and initial conditions until the model simulation matches the observations of growth. Examples involving a previously‐developed growth model indicate that reasonably accurate simulations can be made for three gramineous crops (grain sorghum, corn, and spring wheat) by calibrating a set of parameters and initial conditions that affect leaf area appearance and senescence. It is proposed that the effectiveness of this procedure in using infrequent growth observations and the ability to obtain these observations using nondestructive measurement techniques make this modelling procedure feasible for use in practical agricultural applications.
Reverse Water Flow in Sorghum Roots
Authors: Xu Xudan , Bland William L.
Published: July 2010

Efflux of water from plant roots has implications for nutrient uptake in dry soil, the effectiveness of collection of water from deep in the soil, water parasitism among plants, and the ability of roots to resume water uptake after exposure to dry soil. We measured the minimum soil water potential required for reverse flow in sorghum [Sorghum bicolor (L.) Moench], the diurnal time‐course of the efflux, and differences between sorghum genotypes in reverse flow. A split‐root system was used in which near‐surface roots were subjected to drying and deeper roots were in free water. Efflux of water to the dry soil could first be detected at a soil water potential of about ‐0.55 MPa, or across a soil water potential gradient of 0.55 MPa, a smaller value than previously reported to induce reverse flow. Outflow was 5 to 6% of daily transpiration during the periods of highest water use. Differences between the genotypes in the amount of water emitted and recaptured and the mean water content of the soil were mimicked by a computer simulation of water uptake and release by plant roots. Plant parameters contributing to simulation of the observed behavior were the relationship of leaf water potential to stomatal closure and root length density. Water efflux from roots into the pot soil began at 1430 h, with the peak rate occurring near the end of the daytime period (1900 h) and cessation of outflow by 2400 h. Initiation of outflow during daytime is both physically reasonable and simulated in computer models. The time‐course of outflow, however, was not correctly simulated. Measurements should be made at 1 hour time resolution to capture all reverse flow.
A Crop‐Specific Drought Index for Corn: II. Application in Drought Monitoring and Assessment
Authors: Meyer Steven J. , Hubbard Kenneth G. , Wilhite Donald A.
Published: July 2010

How drought is perceived, and defined, determines the likely response of decision makers to a drought event. Since drought response is usually based on some type of assessment of the severity and duration of the event, a critical element of a drought response strategy lies in the incorporation of objective and reliable impact assessment techniques. However, a long‐standing problem in responding to past droughts has been the lack of reliable techniques for monitoring the drought event and assessing probable impacts. This paper describes a new method to reliably monitor and assess weather's probable impact on corn (Zea mays L.) yields, on a crop reporting district (CRD) level, any time during the growing season. The 1990 growing season was used to demonstrate the ability of the crop‐specific drought index (CSDI) to monitor and assess the condition of East Central Nebraska's corn crop every 10 days, starting 17 June, until a definitive projected CSDI value became established. A 3‐wk hot and dry spell (24 mm of rainfall during the 3‐wk period 28 June‐17 July) that immediately preceded silking resulted in a 17 July CSDI assessment, based on the climatological record of the CRD, that projected yields to be only 63% of the maximum yield previously attained in this CRD. However, a substantial rainfall event during the week of silking alleviated the stressful conditions, and by the beginning of the early grain fill period (blister stage), a 6 August CSDI assessment projected the final CSDI value to within 3% of the actual CSDI (projected and actual yields were 86 and 83%, respectively, of the maximum yield previously attained in Nebraska's East Central CRD). The results of this study demonstrate that the CSDI can monitor and assess weather's impact on corn yields on a CRD level.
Soil Tillage and Windbreak Effects on Millet and Cowpea: II. Dry Matter and Grain Yield
Authors: Leihner D. E. , Buerkert A. , Banzhaf J. , Serafini P. G.
Published: July 2010

In the West Africa Sahel, sand storms occurring early in the growing season may severely damage emerging crops. This study was conducted to determine the Influence of ridges and windbreaks on growth, water use and grain yield of millet, Pennisetum glaucum (L.), and cowpea, Vigna unguiculata (L.) Walp. A field trial was carried out from 1985 to 1987 on a Psammentic Paleustalf in southern Niger using 12 ha of land fallowed over the previous 5 yr. Treatments for millet and cowpea were flat and ridged soil preparation and windbreaks spaced at 6, 20, 40, and 90 m. Total annual rainfall was 558, 641, and 363 mm in the 3 yr of the experiment; onset and distribution of the rains varied. Millet total dry matter (TDM) increased as total water use Increased from 250 to 400 mm. Ridging did not change total dry matter or grain yield in millet but increased cowpea grain yield by 90 and 300 kg ha−1 in 2 of the 3 yr. Protection by windbreaks spaced 6 and 20 m apart resulted in a 48 to 90% Increase in early millet TDM and a 74 to 89% improvement of cowpea ground cover. However, these early effects were not sustained throughout the growing period. Average TDM at maturity and grain yields were similar in all windbreak spacings for millet and cowpea. Although windbreaks may not increase yields of two important Sahelian crops, they may help to stabilize longterm crop production by conserving the soil and providing additional marketable commodities if an appropriate selection is made of type of windbreak and species planted.
Inter‐Seasonal Variation in Soybean and Maize Yields under Global Environmental Change
Authors: Sinclair Thomas R. , Rawlins Stephen L.
Published: July 2010

Projected global environment changes will have major influences on crop yields. A very important aspects of crop yields, and societal adjustments to environmental changes, may well be altered year‐to‐year stability in yields. Simulations for three locations in the Midwest with mechanistic growth models for maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] showed important species differences in projected yield stability. Maize yields under global environment changes were approximately equal to current levels and the year‐to‐year yield variability was unchanged. Soybean, however, had higher mean yields under changed global environments as compared to the current environment, and there was substantially greater year‐to‐year variability under possible future environments. This disparity among maize and soybean in mean yield changes and stability across years may have important consequences on crop management and stabilization of food and feed supplies.
Yield Components of Five Kenaf Cultivars
Authors: Webber Charles L.
Published: July 2010

As the USA approaches commercial production of kenaf (Hibiscus cannabinus L.) as an alternative fiber source for paper pulp and other uses, additional information is needed concerning the relationship among kenaf yield components. Kenaf yield components can be important parameters in the selection of the cultivars best suited for specific uses, and in maximizing the production and processing efficiency of a selected kenaf crop. The objective of this research was to examine the yield components of five kenaf cultivars. A 2‐yr study was conducted at Lane, OK, on a Bernow fine sandy loam, 0 to 3% slope, (fine‐loamy, siliceous, thermic Glossic Paleudalf). Kenaf cultivars Tainung #2, Everglades 71, Everglades 41, Cuba 108, and Guatemala 51 were planted on 8 May 1989 and 23 May 1990. In each year plots were arranged in a randomized complete block design with four replications. Plots were hand harvested on 24 Oct. 1989 and 1990. Data collected included stalk and leaf yield, stalk and leaf percentage, bark and core percentage, bark to core ratio, stalk diameter, plant height, and plant population. Everglades 41 had the greatest percentage of stalk by weight (78.5%). Cuba 108 had the least percentage core material (62%), and the greatest bark to core ratio (0.61), while Tainung #2 had the greatest percentage core material (69%) and greatest plant height (299 cm). Tainung #2 also had greater stalk yields (13.8 Mg ha−1) than either Guatemala 51 (11.4 Mg ha−1) or Cuba 108 (10.8 Mg ha−1).
Sub‐Root Zone Layering Effects on Water Retention in Sports Turf Soil Profiles
Authors: Taylor D. H. , Nelson S. D. , Williams C. F.
Published: July 2010

Sports turf areas are often constructed by placing a root zone soil mixture over coarse‐textured layers such as sand or gravel. The objective of this research was to determine the degree to which drainage from and water retention in soil mixtures were affected by properties of the underlying layers. In a laboratory experiment, soil water matric potential energies (Ψm) and mass water contents (θm) were measured to characterize the water relations during and after 48 h of drainage for four soil mixtures when placed over the following subsurface layering treatments: 50 mm of sand over 100 mm of gravel., 150 mm of gravel, 150 mm of sand, and loam soil. For the three treatments composed of coarse‐textured subsurface layers, soil water matric potential energies at the soil mixture/coarse‐textured layer interface after 48 hours of drainage were controlled by the coarse‐textured sublayer and varied from about −0.9 kPa for the gravel sublayer to about −2.4 kPa for the sand sublayer. Water retention in the soil mixture layer was greatest for the gravel sublayer, followed by sand over gravel, while sand and soil sublayers resulted in the least water retained. Generally, the increased water retention from gravel and sand over gravel sublayers resulted from creating a wet zone at the bottom of the soil mixture layer rather than increasing water retention throughout the soil mixture. Where coarse‐textured materials are used as sublayers in sports turf soils, choice of a soil mixture that drains at the matric potential established at the soil mixture/coarse layer interface is critical to avoid extended periods of saturated soil conditions in the root zone soil layer.
Carbon and Phosphorus Losses from Decomposing Crop Residues in No‐Till and Conventional Till Agroecosystems
Authors: Buchanan Marc , King Larry D.
Published: July 2010

An increased knowledge of crop residue decomposition characteristics is a critical component for nutrient cycling studies in agroecosystems. Carbon and P losses from shoot residues of maize (Zea mays L.), wheat [Triticum estivum (L.), emend. Thell], soybean [Glycine max (L.) Merr.], and shoot and root residues of crimson clover (Trifolium incarnatum L.) were compared in no‐till and conventional till systems. Grain crop residues were generally collected from senescent plants following harvest and placed in fiberglass mesh litter bags. Soybean leaf residues, however, were sampled following preharvest abscission, while crimson clover residues were collected at spring anthesis and buried only in a conventional till system. Generally, the changes in C and P content of residues were best described by exponential and/or logarithmic functions. Losses of C and P from crop residues were consistently greater, and more rapid when residues were buried vs. left on the soil surface. Crimson clover shoots lost C and P more rapidly than root residues. Generally, greater initial losses of P than of C occurred in most residues. The lack of correlation between C and P losses is believed to be due to an inital and probably variable inorganic P content that is readily leached prior to the decomposition and mineralization losses of C. Differences in the rate and magnitude of C losses were related to seasonal effects, the initial N and P content, and/or the proportional amount of lignin in the plant residues. Tillage is clearly an important regulator or driving variable for element cycling in agroecosystems.
Resumption of Water Uptake by Sorghum after Water Stress
Authors: Xu X. , Bland W. L.
Published: July 2010

Exposure of roots to dry soil may reduce their ability to absorb water when the soil is rewet. We sought to quantify the effects of the duration of exposure to dry soil and the availability of water in deeper soil layers on resumption of water uptake by roots of Sorghum bicolor (L.) Moench following rewetting of the soil. Plants were grown in a greenhouse in pots, half of which were fitted with a water‐filled reservoir below the pot bottom. Soil was allowed to dry for either 26 or 39 d before rewetting. Reservoir roots were excised at rewatering to limit uptake to roots previously exposed to soil drying. Time courses of plant transpiration and leaf water potential prior to and after rewatering were measured. Longer exposure to dry soil slowed resumption of uptake. After 26 d of drying, plants without reservoirs transpired 63.5% of that of well‐watered controls without reservoirs on the first day following rewatering, compared to 29.4% following 39 d of drying. Water available below the dry soil enabled roots to resume water absorption immediately after rewatering. On the first day after rewatering following 39 d of drying, transpiration relative to well‐watered controls (with and without reservoirs) was 2.6‐fold greater in plants with access to a reservoir than those without. Water‐stressed sorghum showed larger root/shoot and root weight/length ratios than controls.
A Sunflower Simulation Model: I. Model Development
Authors: Chapman Scott C. , Hammer Graeme L. , Meinke Holger
Published: July 2010

In dryland farming systems, opportunities to improve sunflower (Helianthus annuus L.) yields are mostly associated with management decisions made at planting. Dynamic crop simulation models can assist in making such decisions. This study reports the structure of QSUN, a simple and mechanistic crop model for sunflower, and how it accounts for the dynamic interaction of the crop with the soil and aerial environment. The model incorporates several recent approaches to simulation of crop growth in dryland conditions. QSUN estimates growth, development, and yield of a sunflower crop. Daily inputs of temperature and photoperiod drive a phenology submodel to predict stages of emergence, bud visibility, 50% anthesis, and maturity. Using these stages, the growth submodel, driven by daily inputs of radiation, rainfall, and temperature, estimates leaf area production and senescence and soil water extraction. Biomass production is calculated from the amount of radiation intercepted by leaves or from the amount of water accessible in the root zone, depending on whether radiation or water is limiting crop growth. Seed yield is calculated from the allocation of biomass to the grain following anthesis. Sensitivity testing of the model under several irrigation regimes indicated that QSUN was most sensitive to the rate at which partitioning of biomass to grain increased, the ratio of biomass produced to water transpired, and the rate of soil water extraction in a water limited situation. The model was tested against independent data, with actual phenological data and was able to satisfactorily predict leaf area index (r2 = 0.65), total biomass (r2 = 0.96), and grain yield (r2 = 0.93), thus providing a tool for use in simulations studies and to assist in management decision making.
A Sunflower Simulation Model: II. Simulating Production Risks in a Variable Sub‐Tropical Environment
Authors: Meinke Holger , Hammer Graeme L. , Chapman Scott C.
Published: July 2010

In highly variable environments, farmers require quantitative information on production risk to make well informed farming decisions. In many cases this can only be achieved through simulation studies. Thus, the dynamic sunflower (Helianthus annuus L) model QSUN was used, in conjunction with long‐term climate records, to quantify the impact of climatic variability on production. Simulation results will assist farmers in making important management decisions such as if or when to plant, or which maturity type to choose. Simulations were conducted for three maturity types for planting times throughout the year and for two locations in Queensland, Australia (Dalby and Emerald). For both locations, more than 100 yr of daily temperature and rainfall records were available. Two hypothetical soil profiles were chosen to assess the effect on simulated yield likelihood of (i) maximum plant available soil water holding capacity of the soil (PAWC) and (ii) soil moisture content at sowing. The analysis showed that yields not restricted by water availability were higher at Dalby (370 g m−2) than at Emerald (349 g m−2). At Dalby, simulated median yields for soil profiles either full or half‐full (180 mm PAWC) at sowing were around 100 and 60 g m−2, respectively, with very little seasonal variation. At Emerald, median yields (70–90 and 40–60 g m−2 for the full and half‐full profile, respectively) were generally lower and seasonal variations were apparent: highest simulated median yields were achieved for mid‐summer sowings. Yield variability was assessed by comparing median yields to yields at the 75 and 25% probability level. For both locations, this showed that even at the 25% probability level, yields of more than 100 g m−2 can only be achieved if the soil profile was fully charged at planting. The comparison among maturity types showed no clear advantage of maturity type. These results provide farmers with an objective assessment of production risk in environments, where even one lifetime of experience can be insufficient to sample the climatic variability adequately.
ENWATBAL.BAS: a Mechanistic Evapotranspiration Model Written in Compiled Basic
Authors: Evett S. R. , Lascano R. J.
Published: July 2010

ENWATBAL, a mechanistic energy, water balance model originally written in the Continuous System Modeling Program (CSMP) simulation language, was largely incompatible with personal computers (PCs). ENWATBAL.BAS was developed to extend the model application to PCs using BASIC, which is widely available. BASIC functions or subprograms were provided to emulate CSMP language commands including integration, implicit root finding, and generation of dependent variable values from tables of dependent‐independent variable data pairs. The BASIC version is highly modular and thus easier to read and maintain. The verification of ENWATBAL.BAS against ENWATBAL, with identical input data, discretization, and time integration steps, indicated no appreciable differences between the two versions. Runtimes for a seasonal simulation (100 d) were nearly the same (about 5 h) for the compiled BASIC version with a 20 MHz, 80386‐based PC and the CSMP version with a MicroVAX II, and four times faster for a 33 MHz, 80486‐based PC. Discretization analysis showed that soil layer thickness should be no larger than 0.002 m for the surface layer although thickness may increase to as much as 0.2 m for subsurface layers. Parameter sensitivity analysis showed that evapotranspiration estimates changed as expected in response to changes in parameter values for surface roughness length, maximum crop water potential, soil albedo, and crop hydraulic resistance. Many model changes were made to the BASIC version subsequent to the speed comparisons resulting in a more advanced and flexible model. ENWATBAL.BAS is a useful tool for investigating the complex mechanisms of evapotranspiration.
Nature and Characterization of Ammonium Effects on Wheat and Tomato
Authors: Gill Maqsood A. , Reisenauer H. M.
Published: July 2010

The very significant yield increases obtained by adding NH4 to NO3‐supplying hydroponic cultures have, for unknown reasons, not been duplicated in soil systems. This research was conducted to consolidate and extend our knowledge of the effects of added NH4 on plant processes, and to define the plant and culture characteristics requisite to optimal utilization of mixed N sources. Wheat (Triticum aestivum L. cv. Anza) and tomato (Lycopersicon esculentum Mill. cv. 6718 VF) were grown in solution cultures providing variables of N source (NO3, NH4, and NH4NO3), culture buffering, and concentration of NH4 and NH3(aq). Treatment effects on plant growth and composition were evaluated. Wheat grew best in NH4NO3 culture, equally well in NO3 or NH4 cultures buffered at pH 6, and poorest in unbuffered NH4 cultures. Growth enhancement with NH4NO3 was accompanied by increased N intake and synthesis of protein. Lowered yields in unbuffered NH4 cultures were associated with H+ injury to the roots and reduced intake of N and nutrient cations. Toxic effects of NH4 per se occurred when culture concentrations exceeded 16 mmol L−1 for roots. Severity of toxicity was associated with abnormally high root and shoot amide concentrations, and tissue levels of unassimilated NH4 exceeding 50 mmol kg−1. In alkaline cultures, NH3(aq) concentrations greater than 0.028 mmol L−1 for tomato and 0.15 mmol L−1 for wheat reduced top growth, and destroyed the structure and functioning of roots. These detrimental effects of NH3(aq) were related to its concentration in the culture, not to tissue NH4.
Cotton and Soybean Root System Growth in Three Soil Temperature Regimes
Authors: Bland William L.
Published: July 2010

Exploration of the soil by roots has significant implications for both plant growth and soil water dynamics. The important environmental determinants of root growth are identified, but an integrated and quantitative understanding of their relative importance through a range of environments is not yet available. The role of seasonal patterns of soil temperature on root system development throughout a crop’s life was studied in controlled‐environment experiments. Cotton, then soybean, was grown in 1.8‐m deep controlled‐temperature rhizotrons. Three soil temperature regimes were replicated three times for each species. In all treatments of an experiment, the near‐surface (0 to 15 cm) temperatures were equal, to promote similar aboveground growth. This near‐surface temperature was increased during the experiment so as to mimic field conditions typical for each species. One treatment was isothermal with depth, the entire soil column warming the same as the surface. A pattern of subsoil warming similar to that found in regions where the crop is grown was the second treatment, and the third set of columns warmed at roughly one‐half the rate of the second treatment. Rate of downward growth of root systems of both crops increased with the rate at which the soil body warmed. Cotton roots grew downward at 1.7, 1.4, and 0.7 cm d−1 in the treatments used for that study; soybean rooting depth increased at 2.6, 1.2, and 0.9 cm d−1. Results supported the hypothesis that root system growth can be predicted from the local soil temperature of the deepest roots and the temperature‐dependent extension rate of seedling roots.
Energy Exchange and Water Use Efficiency of Field Crops: Validation of a Simulation Model
Authors: Grant R. F. , Rochette P. , Desjardins R. L.
Published: July 2010

Crop canopies exercise some control on the exchange of mass and energy with the atmosphere by regulating their stomatal resistance. A hypothesis is proposed in which regulation of stomatal resistance is controlled jointly by the water status of the canopy and photosynthetic capacities of the leaves in the canopy. This hypothesis was incorporated into an ecosystem simulation model, which was tested against data for mass and energy exchange measured over a growing barley crop at different levels of canopy cover and soil water content. Standard differences (square root of the mean square difference) between simulated and measured hourly values for net radiation, latent heat, and sensible heat over the soil‐canopy surface were <50 W m− during each date for which comparisons were made, which is within the range of experimental error. The hypothesis allowed title model to simulate diurnal changes in canopy stomatal resistance under changing atmospheric conditions that were consistent with those estimated from flux measurement techniques. These diurnal changes allowed the model to reproduce changing relationships between latent and sensible heat fluxes measured at different canopy covers and soil water contents. The diurnal changes in simulated canopy stomatal resistance also allowed the model to reproduce diurnal changes in soil‐canopy net CO2 exchange (SD = 3–4 μmol m−2 s−1) and water use efficiency under changing atmospheric conditions and soil water status. The hypothesis for the regulation of canopy stomatal resistance is simple, and yet allows observed canopy behavior to be reproduced over a wide range of conditions.
Oat Companion Crop Management in Alfalfa Establishment
Authors: Curran Bill S. , Kephart Kevin D. , Twidwell Edward K.
Published: July 2010

Companion crops may compete with alfalfa (Medicago saliva L.) seedlings, but establishment with preemergence herbicides and without a companion crop may enhance the potential for soil erosion. Objectives of this study were to (i) compare alfalfa establishment techniques involving clipping or chemical control of weeds and (ii) determine differences in morphological development of alfalfa grown under several establishment techniques. Experiments were conducted at two locations in eastern South Dakota in 1989. Seven treatments included clipping the oat (Avena sativa L.) companion crop at boot stage, not clipping the oat, two treatments with oat sprayed with sethoxydim (2‐[I‐(ethoxyimino) butyl]‐5‐[2‐(ethylthio) propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one) at either S‐(SES) or 15‐cm (SE15) of oat growth, clear seeding (CS), hand weeding (HW), and a control treatment with no weed control. At Aurora, SD, alfalfa yields were greatest in HW and SE5 treatments. Yields were 24 and 36% less for CS and SE15, respectively, than for SES. At Brookings, SD, yield was also greatest for HW; however, CS had the greatest yield among the conventional establishment techniques. Yield for SES was 15% less than CS. At both locations, alfalfa yield was lowest for the two typical companion crop techniques. For typical companion crop and control treatments, mean tap root length, shoot‐to‐root ratio, and shoot length were reduced compared with other treatments. Subsequent alfalfa yields in 1990 were not affected by establishment technique at either location. Chemical control of an oat companion crop provided greater seedingyear alfalfa yields than typical companion cropping and greater protection from soil erosion than clear seeding.
Path Analysis of Heavy Metal Adsorption by Soil
Authors: Basta N. T. , Pantone D. J. , Tabatabai M. A.
Published: July 2010

Path analysis, a statistical technique that differentiates between correlation and causation, was used to describe heavy metal adsorption by soil. A path analysis model that evaluates the effect of soil pH, CEC, organic carbon content (OC), and clay content on adsorption of Cd, Cu, Ni, Pb, and Zn by soils from two long‐term cropping experiments in Sutherland and Kanawha, IA, was investigated. In general, direct effects of soil properties on metal adsorption were pH > OC > CEC. Path analysis direct effects of pH on Cd (0.83), Cu (0.93), and Pb (0.96) by Galva (fine‐silty, mixed, mesic Typic Hapludoll) soils from the Sutherland experiment were highly significant (P < 0.01). Significant (P < 0.01) direct effects of pH on Cd (0.93), Cu (0.95), and Pb (0.85) adsorption by Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soils from the Kanawha experiment. Significant (P < 0.01) simple correlation coefficients were found between soil pH and Cd (0.64), Cu (0.89), and Pb (0.84) adsorption by Galva soils and between soil pH and Cd (0.82), Cu (0.74), and Pb (0.62) adsorption by Webster soils. Both path analysis and correlation analysis showed that soil pH was the predominant property affecting Cd, Pb, and Cu adsorption by soil. However, path analysis revealed three additional relationships not found by correlation analysis. They included direct effects of CEC on Ni adsorption (0.72*), OC on Pb adsorption (0.35*) by Galva soils, and OC on Cd adsorption (0.59*) by Webster soils. Partitioning of OC direct and indirect effects suggested that adsorption of Pb and Cd by soil organic matter through complexation reactions was more important than adsorption by organic matter CEC sites.
Accuracy of Sap Flow Measurement Using Heat Balance and Heat Pulse Methods
Authors: Cohen Y. , Takeuchi S. , Nozaka J. , Yano T.
Published: July 2010

The heat balance and the heat pulse methods for measurement of sap flow in plants, were compared under conditions of variable evaporative demands in order to evaluate their accuracy. The study was conducted with potted soybean (Glycine max Merr. cv. tamahomare) and corn (Zea mays cv. kakuteru 901) plants housed in a plastic chamber. The computed sap flow was compared to transpiration rate as measured by weight loss. The calibration coefficient for the heat pulse expresses the ratio of actual transpiration rate, Tr (mg s−1), to measured heat velocity, v (mm s−1), multiplied by the stem area, a (mm2). The ratio Tr/(v × a) was 1.01 ± 0.08 and 1.73 ± 0.1 for soybean and corn, respectively. The coefficient was not affected by plant age, size, or atmospheric evaporative demand. Accuracy of measurements using the heat pulse method was poor at low transpiration rate. The heat balance method does not require calibration (except for the gauge factor for estimating the sheath conductance). Transpiration was estimated accurately by this method in both species at low or moderate rates (0.6 L d−1). As the transpiration rate increased, the computed sap flow deviated from the measured transpiration. In soybean, transpiration was underestimated by 20%, while in corn, it was overestimated by 25%. Results indicated that the basic assumption of the heat balance method (i.e., that the stem surface temperature is considered a reliable measure of the average temperature over the entire cross‐sectional area) may be incorrect either at high or fluctuating flow rates, or whenever the water conducting system is distributed unevenly in the stem cross section.