Validation studies for fertilizer recommendations made by Nutrient Expert in Yunnan province

Three field experiments were carried out to validate fertilizer recommendations for maize made by the Nutrient Expert (NE) in Yunnan province in 2013. The experiments were arranged in three locations with different soil fertility from low to high. The experiments consisted of seven treatments including the optimal treatment (OPTE) generated by the NE, the treatments omitting N (OPTE-N), P (OPTE-P) or (OPTE-K), the check (no fertilizer), OPTE, farmers’ practice (FP) and soil test-based recommendations (OPTS). Each treatment repeated three times. The OPTE at the three locations according to soil fertility were 175-83-118 kg N-P₂O₅-K₂O/ha for the high, 180-64-96 kg N-P₂O₅-K₂O/ha for the medium, 225-94-140 kg N-P₂O₅-K₂O/ha and for the low. The N rates in the FP and the OPTS were more than doubled compared to the OPTE. Nitrogen was used as urea, P as single superphosphate and K as potassium chloride. Phosphate was used as basal application at seeding, N was spilt into one basal application at seeding and two side-dressings at 45 d and 60 d after seeding as proportions of 21:31:48, and K was split into one basal application and on side-dressing at 45 d after seeding as proportions of 30:70.
Results showed that different fertilizer treatments significantly affected maize growth and kernel yields at three locations. In the low fertility soil, the OPTE produced the highest maize yield and followed by the FP and the OPTS. In the medium fertility soil, however, the OPTS produced the highest maize yield and followed by the FP and the OPTE. There were no much yield differences in the high fertility soil. In all three locations, the CK treatment produced the lowest maize yield and followed by OPTE-N, OPTE-P and OPTE-K. The first year study confirmed that the NE recommendations produced the similar maize yields with much lower N rates, showing its promising future use in the region, especially in the low to medium fertility soils. The nutrient limiting factors in the region for maize production turned out to be N>P>K.