Adubos verdes e adubação mineral nitrogenada em cobertura na cultura do trigo em sistema de plantio direto

Abstract

The objective of this work was evaluate the effect of different green manures, associated with levels of mineral nitrogen top dressing in the agronomic performance of wheat crop under no-tillage. The experiments were performed in Dourados-MS, Brazil, in different areas and years, and in randomized blocks experimental design, with treatments arranged in a split-plot scheme with four repetitions. In the first crop season, the plots were constituted by hairy vetch (Vicia villosa Hoth) and sunn hemp (Crotalaria juncea L.) and a fallow treatment as control; in the split-plot were tested six levels of mineral nitrogen top dressing fertilization (zero, 30, 60, 90, 120 and 150 kg ha-1). In the second crop season, the plots were constituted by hairy vetch (Vicia villosa Hoth), sunn hemp (Crotalaria juncea L.), velvet bean (Mucuna deeringiana (Bort) Merr.), hyacinth bean (Dolichus lablab L.) and a fallow treatment for comparison; in the split-plot were tested four levels of mineral nitrogen top dressing (zero, 45, 90, and 135 kg ha-1). The source of mineral nitrogen used was urea. Evaluations of cover crops shoot dry mass, nutrient contents in green manures shoot, nutrient contents in wheat leaves, plant height, number of productive tillers per plant, length of spike, number of grains per spike, one thousand-grains weight, hectolitric weight and yield were performed. It was concluded that the growth of green manures before seeding wheat promotes significant increases in yield of theii crop and that the wheat response to the application of mineral nitrogen differs depending on the predecessor culture.