Influence of tillage system and starting N fertilization on seed yield and quality of soybean Glycine max (L.) Merrill

This field polyfactorial trial with soybean was performed on gleyey alluvial soil in 2006-2008. Three tillage systems: conventional, reduced (spring shallow cultivation to a depth of 100 mm followed by drilling), no-tillage and two doses of starting N: 50 kg N/ha, 25 kg N/ha were tested in this trial. The trial was organized in a complete randomized block design with four replicates. All data were subjected to anova, LSD method and regression analysis using Statgraphics. Seed yield was highly significantly (P < 0.01) affected by weather conditions. Weather was the most dominant factor that influenced seed yield. The highest average yield was found in 2008 - 2.77 t/ha, followed by 2.34 t/ha in 2006 and the lowest yield of 1.98 t/ha in 2007. The stage of seed-filling was found as the most sensitive to water stress resulting in a yield reduction. Seed protein and oil were also highly significantly (P < 0.01) affected by weather. This influence, as compared with tillage system and starting N, was much higher. A negative correlation coefficient r = -0.96 was found between protein and precipitation, compared to a positive correlation coefficient r = 0.81 between oil and precipitation. Tillage system affected seed yield highly significantly (P < 0.01). The highest average yield of 2.60 t/ha gave conventional tillage, followed by reduced tillage - 2.39 t/ha and no-tillage - 2.11 t/ha. The results do not support the choice of no-tillage for profitable soybean production on heavy soils. Starting N fertilization had a significant (P < 0.05) influence on seed yield. The average yield difference between the two starting N treatments was 0.05 t/ha in favour of the dose of 25 kg N/ha. This dose was proven as a rational one.