Iron oxide-impregnated paper vs. Bray-1 soil-test methods predicting crop response from phosphate-rock sources

• Published in: Communications in soil science and plant analysis Vol. 35; no. 13-14; pp. 1981 - 1993
• Main Authors: Govere, E.M, Chien, S.H, Fox, R.H
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 03.01.2005; Taylor & Francis
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Bray-1; corn; fertilizer requirements; Fundamental and applied biological sciences. Psychology; greenhouse experimentation; Iron oxide; iron oxides; Phosphate rock; phosphorus; rock phosphate; silt loam soils; soil analysis; Soil science; soil test values; Zea mays; Test method; Bray-1; Soils; Pi; Iron oxide; Phosphate rock
• ISSN: 0010-3624; 1532-2416
• DOI: 10.1081/LCSS-200026826

The effectiveness of a Pi (iron oxide-impregnated paper) method was compared with that of Bray-1 method in extracting phosphorus (P) from an acid Hartsells silt loam (Typic Hapludult, pH 4.8) treated with low-release P fertilizers derived from Dorowa (Zimbabwe) phosphate rock (DPR) with maize (Zea mays L) as indicator crop in a randomized block design greenhouse experiment with three replicates. The fertilizers used were finely ground DPR, partially acidulated DPR (PADPR), a compacted mixture of DPR + triple superphosphate (TSP) + urea + potassium chloride (DTUK) with half of P from DPR and half from TSP, and a commercial grade single superphosphate (SSP) as a standard. The results indicated that the correlation between Bray-1 and Pi-extractable P was high (r = 97***). The regression coefficients for dry matter yield (DMY) and P uptake (PUPT) as a function of Bray-1 P level of SSP (DMY = 1.16 + 0.24Bray-1 P; PUPT = 0.93 + 0.45Bray-1 P) were significantly lower (p < 0.001) than those for DTUK (DMY = 1.16 + 0.43Bray-1 P; PUPT = 0.93 + 0.74Bray-1 P) and PADPR (DMY = 1.16 + 0.47Bray-1 P; PUPT = 0.93 + 0.82Bray-1 P). That is, a given soil-extractable P level with SSP resulted in a lower dry matter yield or P uptake than that from DTUK and PADPR. Thus, Bray-1 underestimated the agronomic effectiveness of DTUK and PADPR with respect to SSP. Based on this greenhouse research, soil testing for fertilizer recommendations using the Bray-1 test may result in two different response functions, one for water-soluble P sources and another for water-insoluble P sources.