Ratio and rate effects of 32P-triple superphosphate and phosphate rock mixtures on corn growth

Abstract

The availability of phosphorus (P) from "Patos de Minas" phosphate rock (PR) can be improved if it is applied mixed with a water-soluble P source. The objective of this study was to evaluate 32 P as a tracer to quantify the effect of the ratio of mixtures of triple superphosphate (TSP) with PR and the rates of application on P availability from PR. Two experiments were conducted in a greenhouse utilizing corn (Zea mays L.) plants as test crop. In the first experiment, the P sources were applied at the rate of 90 mg P kg -1 soil either separately or as compacted mixtures in several TSP:PR ratios (100:0, 80:20, 60:40, 50:50, 40:60, 20:80 and 0:100 calculated on the basis of the total P content). In the second experiment, the TSP was applied alone or as 50:50 compacted mixtures with PR applied at four P rates (15, 30, 60 and 90 mg P kg -1 ) while the sole PR treatment was applied at the 90 mg kg -1 P rate . The mixture of PR with TSP improved the P recovery from PR in the corn plant and this effect increased proportionally to the TSP amounts in the mixture. When compared with the plant P recovery from TSP (10.52%), PR-P recovery (2.57%) was much lower even when mixed together in the ratio of 80% TSP: 20% PR. There was no difference in PR-P utilization by the corn plants with increasing P rates in the mixture (1:1 proportion). Therefore, PR-P availability is affected by the proportions of the mixtures with water soluble P, but not by P rates. Key words: Typic Haplustox, relative agronomic effectiveness, phosphorus recovery, radioisotope PROPORÇÕES E DOSES DAS MISTURAS DE 32 P-SUPERFOSFATO TRIPLO COM FOSFATO NATURAL NO DESENVOLVIMENTO DO MILHORESUMO: A disponibilidade de fósforo do fosfato natural de Patos de Minas (FN) pode ser melhorada se aplicado junto com uma fonte de P solúvel em água. O objetivo desse estudo foi usar o 32 P como traçador para quantificar o efeito das doses e das proporções das misturas de superfosfato triplo (SFT) com FN no aumento da disponibilidade de P do FN. Dois experimentos foram desenvolvidos em casa-de-vegetação com plantas de milho (Zea mays L.) como cultura teste. No primeiro experimento as fontes de fósforo, na dose de 90 mg kg -1 de P, foram aplicadas sozinhas ou em misturas compactadas e em várias proporções de SFT com FN (80:20, 60:40, 50:50, 40:60 e 20:80) calculadas com base no teor de P total, enquanto que no segundo, o superfosfato triplo foi aplicado tanto sozinho como em misturas compactadas com o fosfato natural de Patos e em quatro doses de P (15, 30, 60 e 90 mg kg . A mistura do FN com o SFT melhorou o aproveitamento do P do FN pelo milho e esse efeito foi crescente com o aumento da proporção do SFT na mistura. Se comparado com o aproveitamento do P do SFT (10,52%) pelas plantas o aproveitamento do P do FN (2,57%) foi baixo, mesmo na proporção de 80% SFT: 20% FN. Não houve diferença no aproveitamento do P do PR entre as doses da mistura na proporção de 1:1. Portanto, a disponibilidade de P do FN é afetada pela proporção das misturas com a fonte solúvel de P, m...

Phosphorus utilization by corn as affected by green manure, nitrogen and phosphorus fertilizers

“…Prochnow et al (2004) obtained similar results with wheat plants. The percentage and the plant shoot-amount of P derived from the fertilizer (Figures 1 D and E) followed the linear behavior of accumulated P. This effect had also been verified by Franzini et al (2009) in corn plants. Both variables, however, behaved differently in the presence of sunn hemp or millet, again, with higher values for sunn hemp, which agree with the greater P quantity provided by the millet (0.220 g per pot) compared to sunn hemp (0.160 g).…”

“…Due to the low values of available P in the soil, there was a high increase in the dry matter weight of corn plants after the addition of the first P rate, with lower increases in the subsequent rates. The quadratic increase in the dry matter yield in response to P rates is commonly observed (Chien et al, 1996;Franzini et al, 2009).…”

“…Thus, one possible, effective P fertilization strategy is to incorporate green manures into soil -mainly P accumulating crops -along with water soluble P fertilizers. This would supply readily available P to the crops in the early growth phase (Grant et al, 2001), and the P from organic residues could become available further on (Ryan et al, 2007).…”

“…Studies using the 32 P tracer methodology on the P dynamics in the soil-plant system, mainly evaluating the efficiency of soluble phosphate fertilizers, have shown that the crops rarely utilize more than 10% of the applied amount (Franzini et al, 2009).…”

Soybean yield in response to application of phosphate rock associated with triple superphosphate

“…As an alternative to the use of superphosphates, phosphate rocks or an association of both sources can be used to manage P fertilization with sources presenting distinct solubility traits (Chien et al, 2009). The joint utilization of these sources can be either accomplished by applying combinations of phosphate rock and soluble sources (Chien et al, 1987;Franzini et al, 2009aFranzini et al, , 2009bNachtigall et al, 1989;Menon et al, 1991;Prochnow et al, 2004b;Villanueva et al, 2006) or by applying them separately but in the same area (associated use).…”