Export of soil macronutrients in area cultivated with maize to feeding feedlot steers

Abstract

The maize cultivated for forage requires special care with soil management. The nutrients exportation by silage might cause reducing of soil fertility, with consequent decrease of yield and nutritional quality of posterior crops. The aim of this work was assess levels of macronutrients in maize plant fragments (stem, leaves, bracts plus cob and grains), at stage of ensilage, in entire plant (silage forage) and in the mature grains; measure the nutrients exportation from soil by forage or grains. After, two diets were used in feedlot cattle, first was based on silage and other based in grains, to appraise the potential of nutrients to return into soil by manure and the final account of nutrients balance. The levels of N, P, K, Ca and Mg from forage were, respectively: 1,37; 0,24; 0,81; 0,2 and 0,22%; and in grains: 1,8; 0,28; 0,34; 0,12; and 0,11%. The fertilization performed was enough to supply extracted nutrients when was harvested only grains, promoting deficits in soil of 93 kg ha-1 of N and 84 kg ha-1 of K when was harvested forage. The manure of animals feed with silage+concentrated, compared to diet without roughage (80% grains and 20% protein core), cycled different amounts of N (276,28 vs 59,37), P (128,12 vs 33,37), K (58,32 vs 5,38), Ca (177,7 vs 78,89) and Mg (43,64 vs 11,81) in the cultivated area. The evaluated production systems presented capacity to maintain the levels of nutrients at soil through replacement via manure, and might contribute to the enrichment of fertility and reduce costs with mineral fertilizers in successive crops. The system which forage was used presented deficit of 25 kg ha-1 de K, probably due to insufficient amount of K applied, which recommendation is frequently made to grain production.