Soil preparation epochs and fertilizations for subsistence crops under mulching

Abstract

As alternative for planting crops in the humid tropics without the use of fire, studies point out for the adoption of cultural practices that simulate the cycles of the nutrients of the native vegetation, as the adoption of mulch and contributions of nutrients. The objectives of this work were to evaluate the effect of different epochs of soil preparation and fertilization on the production and on the state nutritional of the crops. The work was realized in Igarapé-Açu county, Pará state, in a argissolic cohesive Yellow Latossol (Oxisol). The experimental design was the randomized complete block, in split-plot. In the plots were studied the planting epochs: Epoch 1 - planting on January, 1998; Epoch 2 - planting on March, 1998; Epoch 3 - planting on May, 1998; Epoch 4 - planting on July, 1998. The studied crops were corn (Zea mays L.), cassava (Manihot esculenta Crantz), rice (Oriza sativa L.) and cowpea (Vigna unguiculata L.). In the split-plots, were studied two fertilization levels: Fertilization 1, with NPK and fertilization 2, with NPK + additional level of P–triple superfosfate. After the manual clearing of the secondary vegetation, the aboveground plant biomass was immediately chopped with a tractor-propelled silage chopper and the material was uniformly distributed over the experimental area in the form of mulching. The soil was sampled at the depths of 0-10, 10-20, 20-30, and 30-50 cm. The experimental data were submitted to the variance analysis and the Scott-Knott test at the 5% level was used. Except for the organic matter and the pH, the others attributes stay unaltered or increased their amounts. The foliar content of the nutrients were in appropriate levels except for N, P and K in the corn plants, S and B in the cassava plants, Ca and Mg in the cowpea plants and K in the rice plants at harvesting time. The plants of the four crops presented the nutrients accumulation averege in the following decreasing order: N > K > Ca > Mg > P ≥ S > Cu ≥ Mn ≥ Fe > Zn > B. The nutrients exportation ocurred in the decreasing order: N > K > Ca > P ≥ Mg ≥ S > Cu > Fe ≥ Mn > Zn > B. The four crops presented productivities than the average productivity of Pará state. The delaying of the corn planting showed that one can obtain up two crops in the system in successive plantings. The cassava planting in the dry season didn't affect its production. The delaying the in cowpea planting provoked a decrease in its production. The rice crops of dry season, tended for smaller productions, except for the rice planted after cowpea. The fertilization 2 with additional level of P, provided increments of 12, 15, 39, and 87% in the productions of cassava, rice, corn and cowpea crops, respectively