Biological P cycling is influenced by the form of P fertilizer in an Oxisol

Andrew J Margenot,Sanjai J Parikh,Rolf Sommer,John Mukalama

doi:10.1007/s00374-017-1226-9

Abstract

Phosphate rock (PR) is an alternative fertilizer to increase the P content of P-deficient weathered soils. We evaluated the effects of fertilizer form on indicators of biological cycling of P using an on-farm trial on a Rhodic Kandiudox in western Kenya. Treatment plots were sampled after 13 cropping seasons of P applications as Minjingu phosphate rock (PR) or as triple super phosphate (TSP) (50 kg P ha−1 season−1), as well as a P-unfertilized control (0 kg P ha−1 season−1). Soils (0–15 and 15–30 cm) were analyzed for microbial biomass P (Pmic), activities of acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase, and sequentially extractable P fractions. P additions as Minjingu PR yielded 299% greater Pmic than TSP at 0–15-cm depth despite similar labile P concentrations in the two P fertilization treatments and stimulated activities of acid phosphomonoesterase (+39%). When added in the soluble form of TSP, a greater percentage of total soil P was present in mineral-bound forms (+33% Fe- and Al-associated P). Higher soil pH under Minjingu PR (pH 5.35) versus TSP (pH 5.02) and the P-unfertilized treatment (pH 4.69) at 0–15-cm depth reflected a liming effect of Minjingu PR. The form of P fertilizer can influence biological P cycling in weathered soils, potentially improving P availability under Minjingu PR relative to TSP via enhanced microbial biomass P and enzymatic drivers of P cycling.

Highlights

Phosphorus (P) deficiency remains a key constraint to agricultural productivity in weathered soils of sub-Saharan Africa (Nziguheba et al 2016)
Though permanganate-oxidizable C did not differ by P fertilizer form, Minjingu phosphate rock (PR) increased Soil organic carbon (SOC) (+10%) at 15– 30 cm depth (p = 0.069) compared to triple super phosphate (TSP), a trend that was weaker at 0–15 cm depth (p = 0.132)
Pfertilization of an acid, weathered soil in western Kenya for 13 cropping seasons produced changes in indicators of biological P cycling depending on the form of fertilizer, Minjingu phosphate rock (PR) or triple super phosphatase (TSP)

Summary

Introduction

Phosphorus (P) deficiency remains a key constraint to agricultural productivity in weathered soils of sub-Saharan Africa (Nziguheba et al 2016). In many parts of sub-Saharan Africa, phosphate rock deposits are an economical alternative to TSP (Jama and Van Straaten 2006; Nandwa and Bekunda 1998). Though less soluble than TSP, Minjingu PR exhibits sufficient dissolution in acid, P-deficient soils to secure comparable or greater improvement of yields in the medium-term (>3 years) (Szilas et al 2007b). It is not known how P fertilization in the form of Minjingu PR versus TSP may affect biological cycling of soil P, which in weathered soils is considered key to plant availability and could modulate long-term response to P recapitalization strategies

Methods

Results

Discussion

Conclusion