Phosphorus fractionation and crop performance on an alfisol amended with phosphate rock combined with or without plant residues

The effects of Sokoto phosphate rock (PR) and plant residues on soil phosphorus (P) fractions and crop performance was studied in the field on an alfisol in the derived savanna of southwestern Nigeria.The plant residues studied were leaves of Dactyladenia barteri, Flemingia macrophylla, Gliricidia sepium, Leucaena leucocephala, maize (Zea mays) stover and rice (Oryza sativa) straw. They were applied alone or in combination with phosphate rock. The PR was applied at a rate of 60 kg P ha-1 and the plant residues at 5 ton dry matter ha-1 during the onset of the major rainy season. Plots without PR and plant residues application were included as control. After four weeks incubation period of PR and plant residues, Crotalaria ochroleuca (shrub legume) was planted in 1999 and maize (Zea mays) was planted in 2001 as test crops. When PR was not combined with plant residues, incubation of Dactyladenia residues increased resin P from 0.13 to 0.79 mg P kg-1 at 4 weeks after incubation (WAI). Other plant residues did not cause appreciable changes in resin P. Application of Leucaena residues increased NaOHextractable inorganic P (Pi) from 14.36 to 20.47 mg P kg-1 at 4 WAI. Total extractable P increased underall the plant residues at 4 WAI but decreased at 8 WAI. When PR was combined with plant residues, there were increases in almost all the P fractions under the plant residues at 4 WAI followed by decreases at 8 WAI. Averaged across P levels, addition of Leucaena residues resulted in higher resin P, NaOH-Pi, residual P and total extractable P compared with the other plant residue treatments. Averaged across residue treatments, resin P increased from 0.12 mg P kg-1 to 0.75 mg P kg-1 at 4 WAI and decreased to 0.08 mg P kg-1 at 8 WAI. All other P pools showed similar trends but with less pronounced decreases at 8 WAI. When PR was not applied with plant residues, Crotalaria dry matter correlate positively with NaHCO3-Pi (R2 = 0.59), NaOH-Pi (R2 = 0.53) and total extractable P (R2 = 0.50), while Crotalaria P uptake correlate positively with NaHCO3-Pi (R2 = 0.50) at 4 WAI. Maize grain yield and P uptake did not correlate with any of the P fractions. However, when PR was applied with plant residues, maize P uptake was positively correlated with resin P (R2 = 0.53) while Crotalaria dry matter (R2 = 0.60) and P uptake (R2 = 0.49) correlate positively with NaOH-Po at 4 WAI. Application of PR alone did not affect yields and P uptakes of Crotalaria and maize crops. Compared with the control without residues, Crotalaria dry matter production and P uptake increased significantly when residues were applied. Interaction effects between PR and Leucaena and rice straw residues on Crotalaria dry matter production and P uptake was significant. Interaction effects between PR and plant residues on maize yield and P uptake were not significant. Ourresults suggest that combined application of PR with selected plant residues may enhance P dissolution from PR and improve crop performance in some cases

Evaluation of phosphorus fertilizer rates for maize and sources for cowpea on different soil types in southwestern Nigeria

Flexible phosphorus (P) fertilizer rate recommendation could be based on variations in soil characteristics that affect yield responses. Experiments were conducted in the Department of Agronomy, LAUTECH, on the effects of P rates on maize and P sources on cowpea in four soil types. On average, soil types and P rates influenced maize height and grain yield. Iwo and Egbeda soils supported taller plants than Itagunmodi soil. Phosphorus fertilization enhanced height and grain yield compared with no P. To optimize maize grain yield for Itagunmodi and Egbeda soils, application of 15 kg P2O5 ha-1 was sufficient while for Majeroku and Iwo, it was 30 and 75 kg P2O5 ha-1, respectively. Cowpea grain yield and P uptake were significantly affected by soil types and P sources. Iwo and Egbeda soils supported higher grain weights and P uptake than Itagunmodi and Majeroku soils. Triple super phosphate (TSP) and no P supported higher grain weights and P uptake than rock phosphate (RP) and single super phosphate (SSP)

Organic Residues Affect Soil P Availability, Cowpea Yield And Nutrient Uptake on a Near Neutral P-Deficient Alfisol in Southwestern Nigeria

In the moist savanna zone of West Africa, it has been suggested that application of organic residues may play central roles in increasing the availability of inherent soil phosphorus and the dissolution and utilization of phosphate rock (PR) by food crops. Laboratory incubation study was carried out with plant residues of different chemical compositions (leaves of Flemingia macrophylla, Leucaena leucocephala, and maize stover (Zea mays L.) in pots containing a P-deficient Alfisol from SW Nigeria with ground Togo PR for 3 months to determine the dynamics of Olsen extractable P in the absence of growing plants. Cowpea (Vigna unguiculata L. Walp) was planted in the incubated soils thereafter to evaluate treatment effects on cowpea yield and P uptake. A control treatment (no PR, no plant residues) was included for comparison. The pot trial was laid out as completely randomised design replicated four times. Generally, soil P availability increased with increasing length of incubation. Compared with the initial soil P value of 3.14 mg kg-1, after 12 weeks of incubation Leucaena +PR had the highest soil P (9. 9 mg kg soil-1), followed by Flemingia (7.9 mg kg soil-1) and Flemingia + PR (7.3 mg kg soil-1). Phosphorus availability following incubation of PR was 5.11 mg kg soil-1, 4.2 mg kg soil-1 for the control treatment, and 3.37 mg kg soil-1 for maize stover, which rather immobilized P throughout the incubation period. Cowpea plants grown on Flemingia and Leucaena incubated soils with and without PR produced higher number of pods, grain yield, and shoot dry matter than those grown on PR and maize+PR incubated soils. Total N uptake was not significantly different among the treatments but P and K uptake was significantly higher in plants grown on Leucaena+PR, Leucaena, Flemingia, and Flemingia+PR incubated soils than those grown on the control, PR, and maize+PR incubated soils. These results suggest that plant residues can be selected and incubated in near neutral P-deficient soils to enhance P availability and increase crop yield and P uptake.Key words: Alfisol, cowpea dry matter, length of incubation, Olsen extractable P, plant residues, Togo rock phosphate, West Afric

Phosphorus fractions under planted Pueraria phaseoloides crop-fallow system: A comparison with natural regrowth

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