Doses of Crotalaria juncea: I—Growth, production, recovery, and efficiency of the use of N in broccoli

Resumo

The recommendation for green manure (GM) in cropping systems still has little scientific support, with few studies addressing the effects of nutrient amounts from green manure on the growth and production of the crop. Our aim was to evaluate the effect of doses of the Crotalaria juncea green manure on the growth, production, and efficiency of the use as well as the apparent recovery of N in broccoli crop. Seven treatments were established; the main treatments was with four doses of green manure: 0, 3, 6, and 9 t ha^-1 on a dry matter (DM) basis. The control treatments consisted of mineral fertilization, the treatment with 25 t ha^-1 compost, and another as the absolute control. Comparatively, production under the absolute control was less than all other treatments with green manure doses. The production of plants grown with 25 t ha^-1 compost was superior to that of plants grown with dose of 0 t ha^-1 and similar to that obtained with 3 t ha^-1; however, it was inferior to those produced with doses of 6 and 9 t ha^-1 green manure. The highest percentage of N recovered (REC N) by the broccoli plants was observed close to a dose of 3 t ha^-1 green manure, with a maximum point of 37.90% (2.8 t ha^-1), while in larger doses of 6 and 9 t ha^-1 showed estimated values of 31.91% and 20.49%, respectively. The physiological efficiency of the use of N (EFUN) showed an effect similar to REC N, with higher EFUN from lowest to highest dose of green manure, that is, 3, 6, and 9 t ha^-1, with estimated values of 70.41, 62.45, and 26.02 g DM per g of N uptake, respectively. The mass amounts of applied C. juncea influenced positively on the growth and productivity of broccoli. The lower mass of applied green manure increases the physiological efficiency of the use of N with more apparent recovery of the applied N.