Agronomic and Financial Benefits of Phosphorus and Nitrogen Sources in Western Kenya

Abstract

A better understanding of the agronomic and economic benefits of integrating organic and inorganic fertilizers is essential for their wide-scale dissemination and adoption in smallholder farming systems in developing countries. Field studies were conducted for 10 cropping seasons (1996)(1997)(1998)(1999)(2000) on a Kandiudalfic Eutrudox soil to compare the effects of Minjingu phosphate rock (MPR) and triple superphosphate (TSP) on the yield of maize (Zea mays), in combination with three nitrogen (N) sources: urea, Tithonia diversifolia and Sesbania sesban leafy biomass. Urea and tithonia were applied to provide 60 kg N ha −1 . Phosphorus (P) from either MPR or TSP was added either once at 250 kg P ha −1 at the beginning of the experiment or annually at 50 kg P ha −1 for five years, the two rates representing two P recapitalization strategies. From the second year, potassium (K) was added to half of each plot to correct for the deficiency that emerged. Over the 10 cropping seasons, the agronomic and economic benefits of the two P recapitalization strategies were similar and were not influenced by the P sources used. With N and K application, both P sources resulted in at least a two-fold maize grain yield increase over the control with no P application that averaged 1.1 tons ha −1 . Comparing the N sources, although urea and tithonia had similar net benefits when P was applied, the total cost associated with tithonia was considerably higher. Without P application, sesbania fallow was the most financially attractive option. Sesbania fallows as an N source were also least sensitive to increases in the price of fertilizers and the cost of labour although the financial benefits of this system remained low in the absence of P and K application.

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

“…Ameliorating P deficiency can be accomplished by recapitalizing soils with P inputs (Buresh et al 1996;Sanchez et al 1997). Acidulated P fertilizers such as triple super phosphate (TSP) offer soluble and rapidly available P, but access and affordability limit their use by smallholder farmers (Jama and Kiwia 2009;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).…”

Maize Residue Interaction with High Quality Organic Materials: Effects on Decomposition and Nutrient Release Dynamics

“…For many years, low-input agricultural technologies such as short duration planted tree fallows and green manuring with tree or crop residues have been demonstrated to offer a costeffective mechanism for increasing crop yields [17,28,36]. Despite experimental evidence that the application of organic materials improve overall soil fertility and crop yields [2,16,22], the selection of appropriate plant materials for soil fertility improvement and maintenance remains a major challenge in low-input agricultural systems [12].…”

The Use of Phosphate Rocks in East Africa: A Review

“…The financial benefits, just like the RAEs, of using PRs vary widely. Jama and Kiwia, (2009) found that the agronomic benefits of TSP and MPR were similar but TSP had a slight edge over MPR in financial benefits. Opala et al (2013) reported negative financial benefits over three seasons when BPR and MPR were used with urea as the N source in western Kenya (Table 3).…”