R. K. Bacon

Genetic variability in nitrogen utilization at four growth stages in soft red winter wheat

Abstract Studies were conducted to determine relationships among nitrate reductase activity (NRA), dry weight (DW), nitrogen (N) uptake, and N concentration in soft red winter wheat (Triticum aestivwn L.). Data were collected for three growing seasons from field plots grown on a silt loam and one growing season on a sandy loam. Ten cultivars were measured under field conditions with plant samples taken at Feekes Growth Stages 6, 10, 10.5, and 11.1. NRA was measured using an in vivo assay method on fully expanded leaves representing the upper most part of the canopy. Results indicated that N uptake was highest during Stages 10.5 to 11.1, although not significantly different for all cultivars. Few differences were found among cultivars for N concentration. The NRA measured under field conditions was more stable at Growth Stage 6. Path coefficients between NRA and DW, N uptake, and N concentration varied considerably depending on the growth stage, indicating that selection for N utilization using one or more...

COMPARISON OF SINGLE CROPPING, RELAY CROPPING AND DOUBLE CROPPING OF SOYABEANS WITH WHEAT USING CULTIVAR BLENDS

Comparisons of single cropping, double cropping and relay cropping of soyabeans ( Glycine max ) with wheat ( Triticum aestivum ) were made at two sites in Arkansas over a two-year period. The comparisons were made using both soyabean blends and their component cultivars. In relay cropping the yields of pure lines of soyabeans were reduced by 17% compared with single-cropped soyabeans, but the yield of wheat in relay cropping was 15% less than in double cropping. Double cropping reduced the branch number, plant height, node number and leaf area of soyabeans compared with single cropping, but relay cropping reduced only node number and leaf area. Both double cropping and relay cropping gave greater land equivalent ratio (LER) values than single cropping, and double cropping gave greater LER values than relay cropping. Net returns were lowest with single cropping and greatest with double cropping. Soyabean blends gave yields similar to the mean of the component genotypes in all three cropping systems, and the net returns of blends were similar to those of the means of component genotypes.

Relation of nitrogen utilization to yield components in soft red winter wheat

Abstract This study was conducted to characterize soft red winter wheat (Triticwn aestivum L.) cultivars for nitrogen (N) utilization efficiency and to determine which traits were most affected and the predictive value of these traits. Grain yield, number of spikes per m2, kernels/m2, kernels/spike and 1,000 kernel weight (TKW) were measured at maturity. Data were collected for three growing seasons from field plots grown on a silt loam and one growing season on a sandy loam. Results indicated that N utilization efficiency was not associated with grain yield. Kernels/m2 had the highest correlation with grain yield (r = 0.50) of the yield components. Kernels per spike had a correlation of 0.43 with grain yield. However, TKW was not correlated with grain yield. There was variation among cultivars as to how the yield components produced final grain yields. Path coefficients indicated a strong positive direct effect for kernels/spike on grain yield and N utilization efficiency. Kernels/spike was found to be t...

Correlation and Calibration of Mehlich‐3 Phosphorus Recommendations for Winter Wheat Following Rice in Arkansas

Abstract Accurate soil‐test based fertilizer recommendations depend on the correlation between nutrient concentrations extracted by routine soil tests and crop response to fertilization. In Arkansas, phosphorus (P) deficiency of soft red winter wheat (Triticum aestivum L.) grown following rice (Oryza sativa L.) is commonly observed from December through February. Data from 18 studies evaluating yield response of wheat following rice to P fertilization in Arkansas were summarized to i) correlate Mehlich‐3 P (1:7 extraction ratio, M3P1:7) with relative yield response, and ii) define the critical M3P1:7 threshold and P fertilizer rates needed to optimize wheat yields. Relative grain yield was regressed against the linear and quadratic terms of M3P1:7. The relative yield of unfertilized wheat increased nonlinearly (r2=0.54) as Mehlich‐3 P increased. The critical M3P1:7 concentration was 19 mg P kg−1 for the 95% relative yield level. The linear terms for M3P1:7 and P fertilizer rate and their interaction described a significant (P<0.001) relationship with relative wheat yield. Recommendations for P fertilizer rates can be made using the multiple regression equation where the targeted relative wheat yield is a continuous function of the soil M3P1:7 and P fertilizer rate, or several soil‐test P categories can be defined and each assigned a single P fertilizer rate that will produce near optimum yields. The M3P1:7 boundaries defining each soil‐test P level were <10 mg M3P1:7 kg−1 for “very low,” 10–14 mg M3P1:7 kg−1 for “low,” 15–19 mg M3P1:7 kg−1 for “medium,” 20–30 mg M3P1:7 kg−1 for “optimum,” and >30 for “high” with recommended P rates of 35, 30, 25, 11, and 0 kg P ha−1, respectively. Fertilization recommendations are specific for winter wheat grown on silt loam soils following rice in the rotation, and are correlated and calibrated with soil‐test P from composite soil samples collected after rice harvest.