Behaviors of Some Soybean Cultivars (Glycine max L.) Yield to Planting Dates and Different Phosphorus Fertilizer Rates

Soybean production components such as planting date, cultivars and phosphorus fertilizer rates affected soybean yield. Two field experiments conducted in extensive field at El-Gahrbia district, Egypt during 2015 and 2016 seasons. The goal of this research was aimed to investigate the influence of sowing date at 1th May, 15th May and 31th May and three phosphorus fertilization rates, i.e. 0, 37.2 and 74.4 kg P2O5/ha on the performance of three soybean (Glycine max (L.) Merrl) cultivars i.e. Crawford, Giza 22 and Giza 111 on growth, yield and seed quality. The tallest plants, the thick stem, highest branches number/plant, pods number/plant, seed number/pod, weight of 1000 seed and seed yield/ha were recorded from sown early on first May in the both seasons. The tallest plants, the thick stems and highest number of branches/plant were recorded from sown Crawford cultivar. Whereas maximum number of pods/plant and number of seed/pod were found from sown Giza 111 cultivar in the both seasons. Increasing phosphorous fertilizer rates significantly increased all studied cultivars of seed yield and yield components. Tallest plant, the thick stem, the highest branches number/plant, pods number/plant, seed number/pod, weight of1000 seed and seed yield/ha were produced from phosphorous fertilizer at a rate of 74.4 kg P2O5/ha in the first and second seasons, respectively.

.7% when sown on 5 th May compared with those sowed on 5 th June and increased seed yield by 17.9% paralleled with those sowed on 20 th April, and augmented seed yield by 10.3% paralleled with those sowed on 20 th May (Kandil et al., 2012). The best sowing date on mid-June, but sowing lately on June avoids due to a reduction in yield and yield components (Yagoub and Hamed, 2013). The greatest seed yield obtained with an early sowing in mid-February and mid-March compared to late-April planting dates (Grichar and Biles, 2014). Significantly, higher yields obtained for earlier planting dates and yield decreased as planting delayed (Hankinson, 2015 Low phosphorus in soil is a major constraint for soybean growth and seed production. Increase phosphorus fertilization from 75 to 375 kg P2O5/ha, soybean yield increased up to 20% compared with the control level. Further P fertilization increase up to 975 kg P2O5/ha did not increase seed yield, but it has influence to seed quality The soil was loamy clay in texture, the pH was 7.9, 7.6, organic matter was 4.8, 4.9 %, 7.7, 7.5, E.C. dS/m -1 , available nitrogen was 15.7 and 16.3 ppm and available phosphorus was 39.6 and 39.1 ppm of both seasons, respectively. Soybean seeds of the studied cultivars obtained from the Field Crops Research Institute, A. R. C., and Giza, Egypt. Seeds of studied varieties infected by specific rhizobia. After plotting and before the planting, sulfate of potassium (48 % K2O) at a rate of 120 kg/ha and phosphorus fertilizers of the form calcium superphosphate (15.5 % P2O5) at above rates supplied to experimental plots. Nitrogen at 36 kg N/ha of ammonium nitrate (33.5 % N) added before the first irrigation for each plot..

Studied Characters:
Ten guarded plants randomly taken from each plot to measure plant height (cm), stem diameter, branches number/plant, pods number/plant, weight of1000-seed (g) and seed weight/plant (g). The two inner of the central area harvested to find seed yield/m 2 in each plot and then calculated in kg per hectare.

Experimental analysis:
The analysis of data collected and statistically by the analysis of variance technique using the MSTAT-C statistical package programmed as described by a procedure of Gomez and Gomez (1991). Lest significant differences test (LSD) at 5 and 1 % level of probability was used to compare between treatment means according to Snedecor and Cochran (1980).Combined analysis between planting dates done according to Waller and Duncan (1969).

Cultivars performance:
Averages of plant height (cm), branches number/plant and pods number/plant significantly affected by soybean studied cultivars, in both seasons. However, stem diameter (cm) in the second season and number of seed/pod, in the first one significantly affected, weight of 1000 seed (g) and seed yield in kg/ha in both seasons insignificantly influenced only in the second one as revealed in Tables (1 and 2

Phosphorus fertilizer rate effects:
Means of plant height (cm), stem diameter (cm), branches number/plant, pods number/plant, weight of 1000 seed (g) and seed yield/ha (kg) significantly affected by phosphorous fertilizer rates in both seasons, except, number of seed/pod insignificantly influenced only in the second one as exposed in Tables (1 and 2). Increasing phosphorous fertilizer rates significantly increased all studied cultivars of seed yield and yield components. The tallest plants (128.7, 136.5 cm), the thick stem (0.79, 1.24 cm), the highest number of branches/plant (5.3, 6.2), number of pods/plant (110.7, 146.8), number of seed/pod (2.79, 2.75), 1000 seed weight (204.8, 211.3 g) and seed yield (2936.9, 2988.7 kg/ha) were produced from phosphorous fertilizer at a rate of 74.4 kg P2O5/ha.Low phosphorus in soil is a major constraint for soybean growth and seed production. Increase phosphorus fertilization from 75 to 375 kg P2O5/ha, soybean yield increased up to 20% compared with the control level. Further P fertilization increase up to 975 kg P2O5/ha did not increase seed yield, but it has influence to seed quality (Antunović et al., 2012). To improve growth and development of plants due to supply phosphorus increased with the supply of assimilates to the seed, which finally gained more weight

Interaction between sowing dates and phosphorus fertilizer rates:
Mean of branches number/plant, pods number/plant, seed number/pod and seed yield/ha (kg)significantly affected by the interaction between sowing date and phosphorus fertilizer rates, but, plant height (cm), stem diameter (cm) and 1000 seed weight(g) insignificantly affected in both seasons. The highest number of branches/plant (5.5, 6.7), number of seed/pod (138.2, 158.0), number of seed/pod (2.88, 2.83) and seed yield kg/ha(3511.2, 3546.2 kg/ha) were obtained from sown early in first May and phosphorus fertilizer at a rate of 74.4 kg P2O5/ha in both seasons as shown in Figs. 5, 6, 7 and 8. However, the lowest values were produced from sown on end May and without phosphorus fertilization. To improve growth and development of plants due to supply phosphorus increased with the supply of assimilates to the seed, which finally gained more weight (Devi et al.,  2012).Phosphorus application at the rate of 60 kg/ha P produced the highest seed yield/ha and 60 kg/ha P recommended for greatest soybean production per unite area (Maga et al., 2017).