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 32P 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.
Highlights
Phosphorus (P) deficiency is a major constraint to crop production in most tropical and subtropical acid soils, and P fertilizers are required to sustain optimum crop yields (Zapata & Zaharah, 2002).Sci
The P rates were 0, 15, 30, 60 and 90 mg kg–1 as triple superphosphate (TSP) either alone or mixed and compacted with phosphate rock (PR) in a 50:50 ratio (7.5 TSP + 7.5 PR, 15 TSP + 15 PR, 30 TSP + 30 PR, 45 TSP + 45 PR) and sole PR applied at the rate of 90 mg P kg–1
The main soil chemical and physical properties determined according to standard analytical methods described by Camargo et al (1986) and Raij et al (2001) are pH (CaCl ) = 4.7; OM = 20 g dm–3; P = 6 mg dm–3; K, Ca, Mg, H+Al, SB and CEC, respectively 0.8, 12.9, 6.4, 31.2, 20.1 and 51.3 mmol dm–3; V= 39.2%; sand, silt and clay, respecc tively 650, 70 and 280 g kg–1
Summary
Phosphorus (P) deficiency is a major constraint to crop production in most tropical and subtropical acid soils, and P fertilizers are required to sustain optimum crop yields (Zapata & Zaharah, 2002).Sci. Supplying a crop the early P requirements with water-soluble P mixed with PR has been shown to be more effective for early root development than applying only PR as fertilizer (Chien et al, 1996). The acidity generated from the hydrolysis of superphosphates in the soil would solubilize the PR and thereby increase P availability from PR (Mokwunye & Chien, 1980). This practice has given positive agronomic results with increase in P utilization from PR by plants (Zapata & Zaharah, 2002; Prochnow et al, 2004). Xiong et al (1996), using 32P-labeled single superphosphate, did not find the same effect for a low reactive PR from China
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