Intergenotypic competition was examined in Triticum aestivum L. em. Thell. populations composed of ‘Ramona 50’ (R50), a tall variety, and ‘D6301,’ a short‐statured variety. Their respective relative heights were about 100 and 75% and relative grain yields in pure stands were about 80 and 100%. Replicate equal‐frequency mixture‐bulk populations were synthesized and maintained without artificial selection or reconstruction for four generations. D6301 decreased in frequency over time with a concurrent decrease in the population yield level. Yield and endpoint yield components were examined in three environments for each genotype in a frequency study where the genotypes appeared in all combinations at 0.125 frequency increments. Population yields were predictable on the basis of pure‐stand performance, but the contribution of D6301 to total yield was significantly below expectations at all frequencies. Complementary competition was indicated because R50 showed a corresponding increase in yield over expectations from pure‐stand performance. Reproductive values were strongly frequency‐dependent for both genotypes, with the competition effect becoming increasingly larger either with decreasing frequency of D6301 or increased frequency of R50. The poor competitive ability of D6301 was expressed as a large decrease in number of kernels per spike and possibly decreased spike number, while kernel weight was not affected. R50 attained its advantage by increased kernel weight at lower frequencies and possibly increased spike number; kernel number per spike remained constant over all frequencies.
The low returns from nitrogen fertilization in central and eastern Sudan stimulated an investigation into the response of grain yields of irrigated wheat (Triticum aestivum L. em. Thell.) to two sources of nitrogen (ammonium sulfate and urea), two methods (broadcasting and sidedressing), and several times of application. Grain yields were unaffected by either source of nitrogen or by method of application. Application of the fertilizer at different stages of growth showed that the addition of fertilizer in the early phases of growth of the crop (at sowing or tillering) gave the greatest response. The response to application at ear emergence was much less. Splitting the nitrogen amount with half given at sowing and half at tillering or ear emergence had no extra merit, and a second application given early in the growing season had more effect on yields than a later one at ear emergence. Growth analysis indicated that the variation in grain yield was mainly a reflection of the effect of the treatments on the leaf area duration (LAD) after ear emergence. Early nitrogen application effectively increased LAD by increasing the leaf area index (LAI) toward the time of ear emergence, while late nitrogen had very little effect on LAI and consequently on LAD after ear emergence.
Intergenotypic competition was studied in populations developed from a hybrid of two wheats (Triticum aestivum L. em. Thell.), ‘D6301’ (short‐statured) and ‘Ramona 50’ (standard‐height). The F2 through F6 generations were grown in the field in two replicate subpopulations without artificial selection. Heights of individual plants, taken from the F3, F4, F5, and F6 bulk populations, were studied in the same environment. Mean height increased and frequency of short‐statured plants decreased markedly from F3 to F6. Height of 62 random lines isolated from each of the F2, F4, and F6 generations showed a decrease in phenotypic variance from F2 to F6. Grain yields of the F2, F4, and F6 bulk populations and the means of 62 random lines (in F3, F5, and F7) indicated a significant increase from the F4 to F6 and from the F5 to F7 generations. At F7 the yield of the bulk population equalled the yield of the lower‐yielding parent, Ramona 50. Variance in yield among lines increased from F3 to F7, but extremely short genotypes did not appear in the F7. Extremely tall genotypes yielded less than those of intermediate height. Thus, in the bulk population directional and stabilizing selection affected both yield and plant height. Some lines in the F7 had higher yields than either parent. Thus, in spite of natural selection against the agronomically desirable short plants, the bulk populations were useful as source materials in selection for increased grain yield.
A three-year study of the effects of sowing date, nitrogen application and seed rate on wheat showed that sowing in mid-October gave consistently greater grain yields than sowing in midSeptember or mid-November because grains were larger and more numerous per head. Nitrogen increased yields but the effect decreased with later sowing. Nitrogen probably increased grain yield by increasing the number of ears, but this effect diminished with higher levels of nitrogen. Grain yield was only slightly influenced by seed rate, and the interaction of seed rate with sowing date or nitrogen was unimportant.
The relative yield decline that is expected under specific levels of water stress at different moments in the growing period is estimated by integrating the FAO Ky approach in the soil water balance model BUDGET. FAO recently developed a water-driven model (Aqua-Crop) for use as a decision support tool in planning and scenario analysis in different seasons and locations. The Aqua Crop model was evaluated with experimental data collected during three cropping seasons; the field experiments were conducted in Setif, Algeria. The objective of the study is to quantify the water stress based on estimation of evapo-transpiration by Aqua Crop model in Durum wheat under stressed conditions.The results of this study proved the efficiency of the Aqua Crop model to quantify the water stress. Total water stress during three cropping seasons (2010)(2011)(2012)(2013) ranged between 0.15 (15%) at Double ridges to anthesis stage to 0.56 (56%) at Anthesis to maturity stage. The AquaCrop model can adequately quantify water stress and can be used to explore management options to improve wheat water productivity.
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