Effect of slash and burn practice and Leucaena leucocephala residue management on nutrient dynamics in the humid lowlands of Ghana

With the view of developing low input agroforestry technology for small scale farmers in the humid lowlands of Ghana, two experiments were conducted at the Institute of Renewable Natural Resources farm at the University of Science and Technology in Kumasi, Ghana. The purpose of the field experiment (minor rainy season, 1994) was to assess the effect of slash and burn practice as a treatment and two treatments of Leucaena leucocephala (Leucaena) residue (fresh Leucaena leaves and twigs) management: 6t/ha surface application and incorporation of 4.5t/ha (4.5I) at planting followed by i.5t/ha (l.5S) six weeks after planting (6 WAP), on soil chemical properties, maize growth, yield and nutrient uptake. The experiment was conducted under a cut-and-carry system (plot without Leucaena hedges). A randomized complete block design with four replications was used to test the treatments. Soil (0 - 20cm depth of profile) and maize tissue samples were collected on three weekly bases, and analysed for their nutrient content. Maize height increment was measured at 3 weeks interval. Maize grain yield was recorded in each treatment at harvest (3 months after planting). The yield of maize in slashes and burn practice was similar to mulching 6t/ha of Leucaena residue. Apparently, this amount of mulch material had no marked improvement as compared to slash and burn. Surface application of the same quantity of Leucaena mulch resulted in 56.78 and 60% increase. Observations from the pot experiment indicated that, the uptake of nitrogen ranged between 46.77 and 49.42% in mulching (9I + 3S) to (18I + 6S) t/ha of Leucaena residue treatments. While 17.74 to 38.48% increase was recorded in surface application of the same amount of mulch, as compared to the slash and burn treatment. However, incorporation of an equivalent of 6.0t/ha of Leucaena residue in pot containing burnt Panicum ash gave 56.07% maize yield and 60.46% increase in nitrogen uptake superior to the pot containing only burnt Panicum ash. These results from the pot experiment are very encouraging and tend to indicate that when Leucaena residue is incorporated into soil in the slash and burn plots, the maize nutrient uptake and maize yield would increase relative to the normal slash and burn plots. In formulating any recommendations of the cut-and-carry system to farmers, however, it would be necessary to test the performance of the treatments imposed in the pots in the field. An economic study to compare the cut-and-carry, alley cropping and slash and burn practice would also be needed. effect on soil chemical properties during the experiment as compared to slash and burn practice. The uptake of nutrients by maize in slashes and burn plots was superior to mulching St/ha of Leucaena. The Benefit/Cost Ratio (B/C) in slash and burn was similar to mulching St/ha of Leucaena, as a result of similar yield of maize grain that generate revenue to both systems. The low performance recorded in mulched plots was attributed to the rate of Leucaena residue applied to the soil. To throw more light on the results obtained in the field experiment, a pot experiment was set up in the major rainy season 1995, to assess the effect of slash and burn practice and different rates of Leücaena mulch on soil chemical properties and nutrient dynamics in maize. A randomized complete block design was used to test the treatments imposed. Soil and maize samples were collected on 4 weekly bases up to the tasseling and fruiting period of maize, and analyzed for their nutrient content. The pot experiment results confirmed the superiority of slashes and burn over mulching 6t/ha of Leucaena residue with regard to soil properties and nutrient uptake by maize plants. Mulching (9I + 3S) to (18I + 6S) t/ha* of Leucaena residue gave 59.65 to 76.42% increase in maize grain yield * (91 + 3S = incorporation of 9t/ha of Leucaena at planting + surface application of 3t/ha of Leucaena S weeks after planting.

Source: KNUST