High Al saturation is one of the limiting factors to intensive cropping of many soils in the Cerrado of Brazil. A field study on the effect of lime rate and depth of incorporation on growth of corn (Zea mays L.) was conducted on an Oxisol (Typic Haplustox) at Brasilia. Lime rates used were 0, 1, 2, 4, and 8 tons CaCO3/ha and depths of incorporation were 15 and 30 cm. Incorporation of 4 tons of CaCO3 to a depth of 30 cm reduced Al saturation from 72% to < 5% on a soil which initially had 1.1 meq Al/100 cm3. Concentrations of soil solution Al decreased to very low levels at pH 5.5.Grain yields of three successive corn crops were increased by liming. Incorporation of lime to a depth of 30 cm resulted in higher yields than incorporation to a depth of 15 cm. Application of MgSO4 to the acid soil increased yields above the nonlimed treatment.Yield responses to liming were due to improved Mg nutrition and neutralization of toxic Al. Root length was increased considerably in the 0‐ to 15‐cm depth and doubled in the 15‐ to 30‐cm depth when Al was neutralized by liming. Increased root development in the 15‐ to 30‐cm depth of the deep lime treatments resulted in greater water utilization from this depth and decreased the detrimental effects of moisture stress at tasseling on corn yields.
e THOMAZ ADOLPHO REIN 2 RESUMO -Este experimento de campo, instalado em janeiro de 1994, teve os objetivos: 1) avaliar a eficiência do fosfato natural de Gafsa farelado (FGF) na recuperação de pastagem de Brachiaria decumbens cv. Basilisk num Latossolo Vermelho-Escuro textura argilosa do Distrito Federal, e 2) verificar efeitos de interações entre fontes de P (fosfato natural de Gafsa e superfosfato triplo (SFT) e incorporação do fosfato com grade e adubação complementar (N, Ca, Mg, K, S e micronutrientes), sobre a disponibilidade de forragem. Os fosfatos foram aplicados na dose de 100 kg ha -1 de P 2 O 5 . O delineamento foi o de blocos casualizados, com parcelas subdivididas, com o tratamento incorporação nas parcelas e o fatorial, fontes de P vs. adubação complementar, nas subparcelas, perfazendo 12 tratamentos com quatro repetições. A resposta à aplicação dos fosfatos só foi efetivada com aplicação simultânea de adubação complementar; a incorporação com grade foi essencial para aumentar a eficiência do FGF; ao ser incorporado com grade, o FGF teve desempenho tão bom quanto o SFT; sem incorporação, o FGF proporcionou produção de matéria seca inferior à proporcionada pelo SFT (p<0,05).Termos para indexação: fosfato de rocha reativo, cerrados, Brachiaria decumbens, adubação de pastagem. EVALUATION OF A COARSE-GROUND GAFSA ROCK PHOSPHATE IN THE RECUPERATION OF A DEGRADED PASTURE ON A CLAYEY DARK-RED LATOSOLABSTRACT -A field experiment was conducted on a Dark-Red Latossol (Haplustox) of the Cerrado of the Federal District, Brazil, to evaluate a coarse-ground Gafsa rock phosphate (CGRP) in the recuperation of a Brachiaria decumbens cv. Basilisk pasture. CGRP was compared with triple superphosphate (TSP) at a P 2 O 5 rate of 100 kg ha -1 both applied by broadcasting. A control treatment without P was included together with two other variables: 1) incorporation of the phosphate with a harrow (with and without) and 2) supplementary fertilization (SF) with Ca, Mg, N, K, S and micronutrients (presence and absence). The response to application of phosphates was only observed with the simultaneous application of SF; incorporation was essential for increasing the efficiency of CGRP; with incorporation, the efficiency of CGRP was equal to that of TSP; without incorporation, TSP was significantly superior to CGRP (p< 0.05).
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