SIMULATION OF THE EFFECTS OF BIOCHAR AND INORGANIC FERTILIZER ON GROWTH AND YIELD OF UPLAND RICE-COWPEA INTERCROP AND SOIL PROPERTIES IN TOLON DISTRICT OF GHANA

Abstract

A three-year short-term study (2017–2019) was conducted in the Guinea Savannah Zone of Ghana to evaluate changes in soil physical and chemical properties as well as productivity of rice-cowpea intercrop system attributable to biochar application under real field conditions. Nutrient leaching in the highly weathered Guinea Savanna soils is often considered a challenge for crop production. Three different sources of biochar were assessed for the rice-cowpea intercrop system's productivity, soil nutrient supply, and soil hydraulic properties at the field by integrating modeling with soil water content measurements in two cropping seasons. The effect of simulations of biochar on upland rice yield and nutrient leach was determined using the APSIM model. The treatments comprised No treatment (control) and 5 t ha-1 rates of high and low pyrolysis (400-700oC) biochar. The three different sources of biochar materials (groundnut shells, poultry manure, and corn cobs) were incorporated into the soil at a depth of 0-30 cm. Biochar plus nitrogen (N), phosphorus (P), and Potassium (K) at rates (kg ha-1) of 45N3030K, and 90N, 60P, 60K, and biochar alone were applied once in May. NPK fertilizer was applied throughout the planting periods. The randomized complete block design with 4 replicates was used. The Agricultural Production Systems Simulator (APSIM) models were calibrated and tested for rice growth and yield, soil water, soil N, surface organic matter, biochar, and soil temperature, and the assessment of model projection was done against independent data sets. The data were used to test the performance of the APSIM model in predicting the crop yield, available soil phase and soil organic carbon on P-deficient soil. The results show that additional amendments to input parameters for the P model, particularly concerning P amount and uptake for subterranean soil layers, may enhance the fit between experimental and model-predicted results. In a variation, APSIM predicted well the growth of cowpea that is well supplied with P, and the residual biochar and N benefits to a succeeding upland rice crop, including the response to additional inputs of N fertilizer. The bond between model predictions and measured data was acceptable for all three different sources of biochar. Biochar enhanced soil hydraulic properties. Leaching by saturated water flux was calculated using soil solution sampled with suction lysimeters and water flux estimates generated by the APSIM model. No significant difference (p > 0.05) was observed in surface saturated hydraulic conductivity or soil water retention, resulting in changes in water percolation for the three sources of biochar plus 45N30P30K. However, due to differences in soil solution concentrations, leaching of inorganic NH4 +, N03 -, P, and K measured in a depth of 70 cm increased (p < 0.05) in the 90N60P60K, whereas NH4 +, N03 -, P, and K leaching decreased for the three sources of biochar plus 45N30P30K, and absolute control. Changes in leaching at 70 cm depth with the three sources of biochar plus 45N30P30K additions were about one order of magnitude lower than 90N60P60K. The findings show that biochar application increases soil solution concentrations and movement of nutrients in the root zone and decreases leaching of NH4 +, N03 -, P, and K, possibly by a combination of retention and enhanced crop nutrient uptake. Rice farmers in Nyankpala-northern of Ghana can improve soil fertility and increase rice yield by applying 5t ha-1 biochar with a combination of cowpea intercrop, biochar, and inorganic fertilizer of N45P30K30