Foliar application of molybdenum on cover crops and response of common beans in successive cultivation

ABSTRACT The effects of foliar application of Mo and use of N from cover crops (Crotalaria juncea L. and Canavalia ensiformis (L.) DC) on the performance of common beans were investigated in this study. Field experiments were carried out in a succession planting system (cover crops - common beans), and nitrate reductase activities were evaluated in the laboratory. The production of cover crops was done in a 2 x 4 factorial scheme installed in random blocks with four replications. The two cover crops sunn hemp and jack bean composed the first factor and the molibdenum doses (0, 40, 80, and 120 g ha-1) the second. These doses were applied as foliar fertilization using sodium molybdate (Na2MoO4) as Mo source. For bean cultivation, an unfertilized control treatment was evaluated.. Sunn hemp showed a linear positive response to Mo application in terms of shoot dry matter and N accumulation, while jack bean showed a quadratic negative response for shoot dry matter; for N accumulation, there was no adjustment of the regression models. Nitrate reductase activity in the common beans was up to three times higher at the Mo dose of 0 g ha-1 when compared to the treatments with Mo application to both cover crops. Cover crops or Mo doses had no significant effect on bean productivity.

摘要 本研究探讨了叶面施钼（Molybdenum, Mo）以及以覆盖作物（猪屎豆Crotalaria juncea L.和洋刀豆Canavalia ensiformis (L.) DC）为氮源对普通菜豆生长表现的影响。本研究采用覆盖作物-普通菜豆连作种植体系开展田间试验，并在实验室测定了硝酸还原酶（nitrate reductase）活性。
覆盖作物种植试验采用2×4因子设计，以随机区组排列，设置4次重复。第一个因子为供试覆盖作物：太阳麻（sunn hemp）与刀豆（jack bean）；第二个因子为钼施用量，分别为0、40、80、120 g·ha⁻¹。钼源采用钼酸钠（sodium molybdate, Na₂MoO₄），以叶面施肥方式施加上述剂量。菜豆种植试验设置了不施肥对照处理。
太阳麻的地上部干物质积累量与氮素累积量均随钼施用量增加呈线性正响应；刀豆的地上部干物质积累量则呈二次负响应，但其氮素累积量未通过回归模型拟合。与两种覆盖作物均施加钼的处理相比，钼施用量为0 g·ha⁻¹时，普通菜豆的硝酸还原酶活性最高可达其3倍。覆盖作物种类及钼施用量均对菜豆产量无显著影响。