MORPHOLOGICAL AND GRAIN YIELD RESPONSES OF SOYBEAN (GLYCINE MAX L.) TO TIME AND INTENSITY OF DEFOLIATION UNDER APPLICATION OF AMINO ACID

The use of amino acids (AA) to increase the uptake of nutrients has been increasing dramatically in recent years. This investigation was conducted in the two successive seasons of 2016 and 2017 on soybean in Golestan Province, Iran, to study the effect of time and intensity of defoliation on quantitative and qualitative characteristics of soybean (Glycine max L.) under the application of AA. A two-year factorial experiment was conducted based on randomized complete block design with three replications. The first factor included the defoliation intensity at three levels 0, 50 and 100%, the second factor included the defoliation time in five levels V1, V3, V5, V7, and R1 (growth stages), and the third factor was the application and non-application of AA. Results indicated that the effects of the defoliation time and intensity, as well as the foliar application of AA, were significant on morphological traits, yield and yield components, and oil and protein contents. In the quadruple interaction, the highest of grain yield (4040 kg.ha(-1)) was observed in the application of AA under defoliation in V5 with 50% intensity during the first year. The lowest value of this trait was achieved in non-application of AA under 100% defoliation in R1 growth stage during both years of the experiment (1585 and 1525 kg.ha(-1), respectively). The maximum grain oil and protein yield were observed in 100% defoliation in V7 growth stage under AA application during the first-year experiment (978.5 and 1499 kg.ha(-1), respectively). Also, the lowest value of the traits was observed in 100% defoliation in the V5 growth stage under non-application of AA during the second year (225.6 and 471.9 kg.ha(-1), respectively). According to the present study, soybean is regarded generally as a defoliation-tolerant crop. Also, foliar application of AA could be used as an effective amendment for preventing defoliation injury in yield and yield components of soybean.