Comparison of phosphorus impregnation and bray 1 soil tests for evaluating plant available phosphorus

Abstract

The relationship between soil test phosphorus and crop response has not been studied for maize (Zea mays L.) in some major benchmark soils of Zambia. The suitable soil test procedure for estimating available P needs to be identified. The objective of this study was to compare two soil test methods, impregnation of phosphorus (Pi) and Bray 1, in predicting P requirement of maize grown in Makeni (fine, mixed Isohyperthermic Udic Paleustalf), Maheba (clayey, kaolinitic, isohyperthermic Haplic Acrustox), and Konkola soil series (fine, oxidic, isohyperthermic oxic, Rhodustalf). The three soil series were treated with 0, 262, 524, and 1,048 mg P per pot as triple superphosphate (TSP). Maize was grown in pots, and after 8 weeks the plants were harvested and analyzed for total P concentration. Phosphorus uptake (P uptake) was calculated as a product of P concentration in the plant and maize dry matter yield. The soil was dried, sieved and analyzed for available P. The available P content estimated by Bray 1, and Pi soil tests was correlated with maize dry matter yield, and P uptake. The P which was extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and more significant (r=0.991 * *), than correlation with P extracted by Pi soil test (r=0.958*). The P extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and significant (r=0.990**), as well as correlation with P extracted by Pi soil test (r=0.958**). The correlation of P extracted from Maheba soil series by Pi soil test and maize dry matter yield followed the same trend as for Makeni series with correlation of r=0.990**. The correlation of P uptake and P extracted by Pi soil test was high but less significant (r=0.955*) than that for Makeni soil series. The correlation of P extracted by Bray 1 soil test with maize dry matter yield was high (r=0.973 *) and significant, but the correlation with P uptake was low and not significant (r=0.879 ns). The available P extracted from Konkola soil series by both Bray 1 and Pi soil tests produced poor and not significant correlation with maize dry matter yield, as well as P uptake. The results show that Bray 1 soil test extracted larger amounts of P from all the three soil series than P impregnation (Pi) soil test. The results further demonstrated that Pi soil test was consistently more closely related to P uptake and dry matter yield of maize grown in Makeni and Maheba soil series. Therefore, Pi soil test was more effective than Bray 1 soil test in evaluating soil solution P that the plant usually takes up.