Synchronizing nutrient release from decomposing organic materials with crop nutrient demand in the semi-deciduous forest zone of Ghana

This study focused on some common plant residues (plant materials) typical of cropping systems in Ghana as sources of plant nutrients. The objectives of the study were to determine the quality, rates of decomposition and mineralization of Chromolaena odorata, maize, stover. Leucaena leucocepala, Gliricidia sepium and Panicum maximum. The study also aimed at regulating the time of nutrient release from plant materials to improve synchrony and increase maize yield by manipulating (mixing) plant materials of contrasting qualities. Laboratory and field experiments were conducted at the Central Agricultural Station, Kwadaso, in the semi-deciduous forest zone of Ghana, which is located at the south — western part of Kumasi, about 8 km away from the city centre. Four experiments were conducted: 1. Determination of the chemical composition of the organic materials. 2. Laboratory- leaching incubation studies to determine nutrient release patterns from the decomposing plant materials incorporated in soils. 3. Field decomposition studies on surface applied and buried plant materials in litter bags to establish decomposition rates in the rainy and dry seasons. 4. Studies on the effect of plant materials of contrasting qualities (maize stover and C. odorata) applied sole (10 T/ha) and mixed, on maize grain and biomass yield. ‘lhese studies were conducted on the Asuansi (Ferric Acrisol) and Ejura (Ferric Lixisol) soil series. Total nitrogen content of the residues ranged from 0.85% in maize stover to 3.5% in G. sepium. Organic carbon ranged from 34.9% in poultry manure to 48.9% in P. maximum; phosphorus ranged from 0.1% in maize stover to 0.76% in C. odorata. Microbial biomass under decomposing C. odorata, G. sepium, and L. leucocephala were higher (1557, 1460 and 1614 μgC/g soil) than P. maximum (1060 μgC/g soil). About twice the available phosphorus was held in microbial biomass. In the rainy season, the decomposition rate constant was 0.0319, 0.0309, 0.0080, 0.0076 and 0.0081 k/day for C. odorata, G. sepium, L. leucocephala P. maximum, and maize stover respectively. In the dry season, the k values were 0.0083, 0.0069, 0.069, 0.0090 and 0.0072 k/day for C.odoral, L. leucocephala, G. sepium, P. maximum and maize stover respectively. Burying of the plant materials reduced the half-life (t50) periods from 18 to 10 days for C. odorata, from 18 to 14 days for G. sepium, from 35 to 18 days for L. leucocephala and from 35 to 20 days for maize stover and P. maximum. Incorporation of C. odorata and maize stover material into Ejura series (Ferric Lixisol) resulted in net mineralization of N (38 mg/kg for C. odorata and 42 mg/kg for maize stover). In Asuansi series (Ferric Acrisol) there was net immobilization of N (8.0 mg/kg for C. odorata and 10.0 mg/kg for maize stover). The highest yield of maize (2556 kg/ha) was obtained in sole C. odorata (10T/ha) treatment. Significantly lower yields (2167 kg/ha) were obtained in the low quality maize stover treatment. Mixing of the residues gave yield values (2411 and 2489 kg/ha) intermediate between sole C. odorata and sole maize stover. In the attempt to control decomposition by mixing organic materials of contrasting qualities to improve synchrony, the quality of the mixture obtained was reduced. The total amount of nutrients available to the crop was compromised resulting in lower maize grain yield. [his study has shown that most organic materials found in farms in Ghana form a good nutrient bank which has never been considered in the nutrient budget of farming systems. Considering the high nutrient content of C. odorata and its abundance in Ghana, it is recommended that this weed is used as green manure, mulching material or composting material t- improve soil fertility.

Source: KNUST