Effect of Combining Organic Residues With Minjingu Phosphate Rock on Sorption and Availability of Phosphorus and Maize Production in Acid Soils of Western Kenya

Abstract

Experiments were conducted in both the greenhouse and the field on highly weathered (Orthic Ferralsol) soils to evaluate the effect of combining on-farm organic residues (chicken manure, farmyard manure, sugar bagasse) with Minjingu phosphate rock (MPR) on soil pH, extractable (available) and sorbed phosphorus (P), and to assess the cost benefit for maize production. The greenhouse study results indicated that, in the first eight weeks of incubation, soil pH increased linearly with increase in MPR rates and decreased thereafter. The available P also increased linearly. Chicken manure and sugar bagasse were most and least effective respectively in reducing P sorption, while there was a significant negative relationship between P adsorption maxima and extractable P. The field experiment data showed that the available P values increased significantly above the control in all the treatments where MPR and organic materials were applied separately or combined. Treatment effects on Langmuir sorption maxima (S max ) in the field were variable. An increase in S max with an increase in MPR rates was noted. However, there was a positive relationship between S max and available P (r = 0.52 to 0.69), suggesting the diversity of factors affecting the complex nature of P dynamics under field conditions. MPR applied alone in the first season gave a significant residual positive effect on maize grain yield for two additional seasons. The economic analysis revealed that a single application of chicken manure (2 t ha −1 ) combined with MPR at 60 kg P ha −1 gave the highest incremental net benefit equivalent to US$ 657 ha −1 during the three maize cropping seasons. I N T RO D U C T I O NPhosphorus (P) is an essential element for plant growth and development. However, among the nutrient elements, P is the most susceptible to fixation (sorption), particularly in acid or calcareous soils so that crops usually recover less P in the short term than other nutrients. Fixation occurs by sorption or precipitation reactions with Fe and or Al oxides in acid soils or Ca in calcareous soils (Chien and Hammond, 1988). Liming acid soils to reduce acidity is one way of overcoming P fixation; alternatively direct application of reactive phosphate rock (PR) or manure can reduce P fixation, or large quantities of P fertilizer can satisfy P fixation sites and thus increase

Effects of Organic and Inorganic Materials on Soil Acidity and Phosphorus Availability in a Soil Incubation Study

“…The findings of the present study are in contrast to others (e.g., [2,4,36]) who reported synergism when OMs such as manures were combined with PRs. These authors combined PRs with OMs of diverse composition and concluded that due to acidifying effect organic acids produced during the decomposition of the OMs, the solubilization of PRs was enhanced thus leading to the higher extractable P values in treatments where PR was combined with OMs than from application of PR alone.…”

“…This coupled with concerns for environmental protection and sustainability has renewed interest in the use of alternative cheaper locally available materials. The use of phosphate rocks (PR) and organic materials has in particular received increased attention in recent years in eastern Africa [2][3][4]. In addition to provision of P, PRs have Ca and Mg which makes them assume a significant role as a potential tool for sustaining soil productivity by reducing soil acidity through its liming effect [5].…”

Phosphorus Sorption and Lime Requirements of Maize Growing Acid Soils of Kenya

“…Therefore, highlands east of RV had moderate to high P sorption, while soils of the west had moderate P sorption. Earlier studies have also reported similar magnitudes of P sorption in some of the Kenyan acid soils (Kifuko et al, 2007;Obura, 2008;Opala, 2009). The differences observed in P sorption capacities between highlands east and west of RV were due to differences in exchangeable Al 3+ and clay minerals (Obura, 2008;Jaetzold & Schmidt, 1983).…”

Recent advances towards understanding and managing Kenyan acid soils for improved crop production

“…These minerals are common in tropical acid soils and are responsible for high P sorption Obura, 2008;Tisdale et al, 1990;Uehabra and Gillman, 1981). Phosphorus sorption in the Kenya acid soils range from moderate to high (Obura, 2008;Kifuko et al, 2007;Kisinyo et al, 2013;Opala et al, 2010a) as P sorptions of 100 to 400 and > 400 mg P/kg are classified as moderate and high, respectively . Kenyan acid soils have different P sorption capacities.…”

“…This was based on the fact that decomposing organic materials produce organic acids that solubilize P from phosphate rocks (PRs) through chelating or complexing action (Kpomblekou and Tabatabai, 1994). Use of OMs to increase the dissolution of PRs has been widely studied in East Africa region Savini et al, 2006;Kifuko et al, 2007).…”