Seed-filling Period Research Articles

Soybean Germplasm Evaluation for Length of the Seed Filling Period 1

Increasing the length of the seed filling period has been suggested as a means of increasing yield in several crop species. The objectives of our study were to measure the seed filling period of soybean [Glycine max (L.) Merr.] plant introductions of Maturity Groups III to V, and to determine whether available data on beginning bloom and maturity of soybean plant introductions could be used to identify potentially useful strains for extending the seed filling period. Strains from the soybean germplasm collection of Maturity Groups III to V were planted in the field in 1978 and 1979. Strains varied for reproductive period (days from beginning bloom to no normal green pods), seed filling period (days from beginning seed fill to physiological maturity) and filling period estimate (days from beginning seed fill to maturity). The range of the seed filling period among strains was 18 to 54 days with a mean of 40 days. Strains were found that had longer seed filling periods than most current cultivars. Strains with longer seed filling periods maintained seed growth at the end of seed filling for a longer time than strains with a shorter seed filling period. The reproductive period, seed filling period, and filling period estimate were highly correlated across years, which indicated genetic control of the characters. The characters were highly correlated with each other which indicated that any of the three methods could be used to evaluate the length of the seed filling period. We suggest that soybean strains from the germplasm collection could initially be selected for length of the seed filling period by using available data for the time between flowering and 95% mature pods. Selected strains could be more precisely evaluated by measuring the seed filling period as conducted in this study.

Sunflower Yield vs. Water Deficits in Major Growth Periods

ABSTRACT SUNFLOWER (hybrid 894) seed yields were mea-sured in response to the imposition of water stress in the growth periods: planting-to-bud stage, bud stage-to-last anther, and last anther-to-physiologic-maturity. Stress level was based upon degree of soil water depletion and an allowable level of leaf xylem pressure depression in mid-afternoon. Yields exhibited linear relationships to seasonal ET with slope for the upper bound function near 84.3 kg/ha-cm. On a relative scale, the upper bound slope indicated a potential yield loss of 1.3 percent per 1.0 percent decline in seasonal ET. When stress was con-centrated in the bud-to-last-anther period the relative yield decline was 3.3 times greater than the reduction in seasonal ET. Near potential seed yields are likely when root zone available water depletions are limited to 50-60 percent in the pre-bud period, 30-40 percent during flowering, and 50-60 percent in the later (after ray petal drop) seed-fill period.

Reduction of yield of Vicia faba by foliar fertilization during the seed-filling period

Vicia faba, in common with other grain legumes, rarely gives economic yield increases in response to soil application of nitrogenous fertilizer either before sowing or at flowering (McEwen, 1970a, b; Day, Roughley & Witty, 1979). The lack of response was attributed to poor uptake of the applied fertilizer particularly at flowering (Day et al. 1979). Garcia & Hanway (1976), however, increased the yield of soya beans from 3695 to 5225 kg/ha with foliar sprays containing N as urea, P, K and S applied during the seed-filling period. Day et al. (1979) using four foliar sprays of the same composition increased yield of V. faba by 361 kg/ha (8·6%) following the uptake of 15% of the 80 kg N/ha applied. However, Robertson, Hinson & Hammond (1977) reported no yield responses of soya beans with up to five foliar sprays of the same composition and noted that those containing ammonium polyphosphate and KNO3 caused leaf damage that significantly reduced yield.

Mineral Depletion and Leaf Senescence in Soya Bean as Influenced by Foliar Nutrient Application During Seed Filling*

Senescence, as judged by the time courses of leaf lamina photosynthesis, soluble protein and chlorophyll contents, was studied in relation to mineral redistribution in field-grown soya beans [Glycine max (L.) Merr.] to investigate the hypothesis that the depletion of nutrients in the leaves by the developing seeds is the cause of soya bean senescence. A mineral nutrient solution was applied to the canopy during the seed-filling period, and the effects on senescence and mineral depletion of the leaves were determined in three cultivars, at two leaf positions, weekly from beginning of seed filling through physiological maturity. The onset of senescence occurred shortly after the beginning of rapid seed filling. Photosynthetic rate declined about 60 per cent within 3 weeks. Protein dropped by 52 per cent and chlorophyll by 48 per cent over the same period. Foliar nutrient application, at a rate previously shown to give significant yield increases in soya beans, increased the concentrations of N, P and K in the leaf laminae, but tended only to delay their decline and failed to either delay the onset or alter the course of senescence. The results of this experiment seem to indicate that, under normal growth conditions, the events of senescence in the soya bean are not causally related to the N, P or K concentrations of the leaf laminae.

Photosynthate and Nitrogen Requirements for Seed Production by Various Crops

Seed biochemical composition was the basis for segregating 24 crops into four distinct groups. Nitrogen requirements of pulses and soybeans were so great that sustained seed growth demanded continued nitrogen translocation from vegetative tissues. This translocation must eventually induce senescence in these tissues, restrict the duration of the seed-fill period, and limit seed yield.