INFLUENCE OF PLANT RESIDUES AND NPK ON SOIL, PLANT NUTRIENTS AND CASSAVA YIELD IN OKA-AKOKO AREA, SOUTH-WEST NIGERIA

Abstract

Field experiments were conducted at Ayegunle and Oke-Oka in the rain forest zone of Southwest Nigeria. The test wastes were sawdust ash (SDA), and chromolaena residues (CR) generated at the sites of study. The first experiment conducted from July 2009 employed (a) 10t/ha chromolaena CR (b) 2t/ha ash SDA (c) 2t/ha SDA + 10t/ha CR(d) 4t/ha SDA (e) 4t/ha SDA + 10t/ha CR (f) 6t/ha SDA (g) 6t/ha SDA + 10t/ha CR and there was a control (no application of wastes). The second experiment conducted from July 2010 involved integrated application of plant residues and NPK 20-10-10 fertilizer (NPKF). In addition to control there were five treatments which were 4t/ha SDA +10t/ha CR (the best of the first experiment), 400kg/ha NPKF (recommended rate),4t/ha SDA + 10t/ha CR +100kg/ha NPKF, 4t/ha SDA +10t/ha CR + 200kg/ha NPKF and 4t/ha SDA + 10t/ha CR + 300kg /ha NPKF. Treatments were replicated thrice in each experiment. Aside from initial analysis of soils at study sites, soil chemical analysis was done at 12 months after planting in both experiments on basis of treatment application. Cassava leaf samples were also collected at 3, 6, 9 and 12 months after planting (MAP) for chemical analysis. Performance parameters determined at the sampling periods were plant height, number of leaves, stem girth, leaf area index, root length and diameter, number and fresh weight of roots. The sandy clay loam soils at the sites of study were slightly acidic, adequate in organic matter (OM), total N, available P, exchangeable K, Mg and Ca (except at Oke-Oka). Nutrients were lower at Oke-Oka and the soil had lower pH. The SDA and CR increased soil pH, OM, N,P,K, Ca and Mg. 4t/ha SDA + 10t/ha CR most increased soil nutrients. Addition of CR to SDA increased soil nutrients. The 4t/ha SDA most increased soil nutrients and pH among the three test levels. In experiment 1, the SDA and CR alone or combined increased plant N,P,K, Ca and Mg, and addition of CR to SDA increased plant nutrients especially at 9 and 12 MAP. The 4t/ha SDA + 10+/ha CR gave highest leaf N,P,K, Ca and Mg. The 4t/ha SDA gave highest leaf nutrients concentrations compared with 2 and 6 t/ha SDA. Highest leaf N was recorded at 12 MAP, highest leaf P and K were recorded at 9MAP, and highest leaf Ca and Mg were recorded at 6 MAP. In experiment 2, plant residues (SDA and CR), sole NPKF at 400kg/ha and combination of residues with NPKF at 100,200 and 300kg/ha increased leaf N,P,K, Ca and Mg. Compared with NPKF, combination of reduced rates of NPKF with plant residues (SDA and CR) increased leaf nutrients, especially at crop maturity (9 and 12 MAP). Leaf nutrients increased with rate of NPKF up to 300kg/ha. Combination 4t/ha SDA + 10t/ha CR + 300 kg/ha NPKF most increased leaf nutrients. In the first experiment, plant residues increased performance parameters at 3,6,9 and 12 MAP significantly. Addition of CR to SDA increased crop performance. The 4t/ha SDA increased crop performance compared with 2 and 6t/ha SDA, percentage increases in root weight being 50,28 and 20% respectively at 12MAP at Ayegunle, and 195, 130 and 47% at Oke-Oka. The 4t/ha SDA + 10t/ha CR had highest root yield of 19.0 and 67.7t/ha at both sites of study respectively. In the second experiment the CR, NPKF and their combinations increased performance parameters significantly. Compared with plant residues (SDA and CR), the 400kg/ha NPKF gave higher values of performance parameters at 3 and 6MAP, while plant residues (SDA and CR) had higher values at 9 and 12 MAP. The parameters increased with rate of NPKF. Combination of plant residues (SDA and CR) with reduced rates of NPKF increased cassava performance relative to sole NPKF. The 4t/ha SDA + 10t/ha CR + 300kg/ha NPKF gave highest values of performance parameters. The control, 4t/ha SDA + 10t/ha CR, 400kg / ha NPKF, 4t/ha SDA + 10t/ha CR + 100kg/ha NPKF, 4t/ha SDA + 10t/ha CR + 200kg/ha NPKF and 4t/ha SDA + 10t/ha CR + 300kg/ha NPKF had root yield of 26.3, 39.9, 33.7, 46.3, 58.8 and 77.4t/ha respectively. Relative to control, the latter treatments increased root weight by 52, 28, 76, 124 and 194% respectively.