Soil test calibration for upland rice in south western Nigeria

The relationship between soil test values and yield response due to fertilization is usually described by response models and would indicate test value where response is expected. Upland rice grain yield was used to define relative yield in terms of yield from control (no fertilizer; or minus nutrient) treatment expressed as percent of complete treatment.Regression analyses show that soil properties were related to both relative yield definitions. Critical nutrient levels and calibration obtained with Cate and Nelson's technique were indicative for soil nutrients. Although relative yield based on fertilizer and control (no fertilizer) treatments has the advantage that many nutrients can be calibrated at the same time, lower R2 values observed in this study with upland rice mean that it cannot be recommended as replacement to conventional relative yield.