Studies on the mineral nutrition of Vigna Sinensis. II: effects of deficiencies of macronutrients on growth, yield and leaf composition

Abstract

Vigna sinensis, varieties "Dorminhoco" and "Pitiúba", was grown in nutrient solution in the presence and absence of macronutrients; leaves (upper and lower) were collected for analysis at the and of the life cyle or when symptoms of deficiency were marked. Variations found in leaf composition agree, as a rule, with what is contained in the literature with regards to other species under the same type of experimental conditions: reduction in concentration in the tissue when the element was absent from the substrate; interionic, counter ion, and dilution effects. The following levels of macronutrients were associated with maximun growth: N=1.97 ± 0.16; P=0.14 ±0.03; K= 3.20 ± 0.36; Ca=5.38 ± 0.41; Mg=0.66 ± 0.14; S=0.15 ± 0.04. As indication of deficiency, on the other hand, the corresponding leaf contents would be: N =1.28 ± 0.13; P = 0.02 ± 0.01; K=0.64 ± 0.10; Ca=1.79 ± 0.24; Mg=0.14 ± 0.05; S=0.05 ± 0.01. Due to the large differences found between foliar composition in the control and the deficient plants it is very likely that under field conditions deficiencis may occur when the level of a given element in the leaves is higher than those presented herein. Dry matter was affected in the following decreasing ords: Complete, -S, -Mg, -P, -K, -Ca, -N; therefore, the lowest yield was obtained in the treatment lacking nitrogen.