Tolerance of Soybean to Defoliation at Pod Formation as Affected by Soil Fertility

Nutrient deficiency reduces new leaf growth, leaf area duration, and photosynthetic activity. Such effects may enhance the sensitivity of soybean to defoliation. This study aimed to assess the effects of soil fertility on defoliation tolerance in soybean at the beginning of pod formation. A greenhouse experiment was conducted in Lages, Santa Catarina, Brazil, during the 2021/22 growing season. Two soil fertility conditions (high and low) and five defoliation levels (0, 17, 33, 50, and 67%) were tested. Defoliation was performed at the R3 stage. The soybean cultivar used was ‘NA 5909 RG’. Leaf area at R3 and R5 was higher under high fertility conditions. At R5, leaf area decreased by 63.8% at the highest defoliation level compared with the control, regardless of soil fertility. Under high fertility conditions, there was a 12.9% increase in leaf area between R3 and R5 in the 67% defoliation treatment compared with the control. Grain yield was 24.7% higher in high fertility soil. An increase in the level of defoliation from 0 to 67% decreased grain yield per plant by 11.9% under both soil fertility conditions. These results suggest that a reduction in soil fertility does not increase defoliation sensitivity in soybean ‘NA 5909 RG’.