ABSTRACT
Higher nitrogen (N) and calcium (Ca) requirements than other macronutrients in Euphorbiaceous species have been pointed out in the literature. Thus, the objective of this work was evaluate the effects of N and Ca combination rates on the visual deficiencies of both nutrients, on the macronutrient status, chlorophyll content and nitrate reductase activity (RNO3-) taken on the recent expanded leaves of Jatropha curcas, as well as to evaluate N and Ca uptake and biomass yield during early plant growth, subjected to 2; 9; 16; 23 e 30 mmol L-1 N rates and 0.5; 1.75; 3.0; 4.25 e 5.5 mmol L-1 Ca rates, in the nutrient solution. Nitrogen, Ca and K concentrations on the recent expanded leaves were changed by N and Ca rates, whereas leaf-Mg concentrations ranged only by Ca supply. Increasing N and Ca rates in solution led to increased leaf area and the leaf biomass yield by 400% and 245%, respectively. On average, N and Ca taken up on leaves accounted for 29% and 39% of the plant uptake. Biomass yield is directly related to RNO3 - activity and chlorophyll content, and the range of N concentration in these leaves related to highest plant dry matter production is 43-45 g kg-1. In conclusion, N supply causes greater impact on the plant biomass yield; however, the effects are more relevant with increased Ca uptake.
Key words:
Leaf area; Plant diagnosis; Jatropha curcas; Nitrate reductase
