Validation Studies for Fertilizer Recommendations Made by Nutrient Expert in Yunnan

Three field experiments were carried out to validate Nutrient Expert® (NE)-based fertilizer recommendations for maize in Yunnan Province. The experiments were conducted at three locations with different soil fertility levels ranging from low to high. The experiments consisted of seven treatments, viz., optimal treatment (OPT) generated by NE, omitting N (OPT-N), omitting P (OPT-P), omitting K (OPT-K), check (no fertilizer), farmers’ practice (FP) and soil test-based recommendation (OPTS). The N-P₂O₅-K₂O fertilization rates in OPT at the three locations were 175-83-118 kg/ha for the high, 180-64-96 kg/ha for the medium, 225-94-140 kg/ha for the low fertility soils. The N rates in the FP and the OPTS were more than doubled compared to the OPT. Nitrogen was supplied using urea, P as single superphosphate (SSP) and K as KCl. Phosphate was applied as basal application at seeding, N was spilt into one basal application at seeding and two side-dressings at 45 days after seeding (DAS) and 60 DAS in proportions of 21:31:48, respectively, and K was split into one basal application plus one side-dressing 45 DAS in proportions of 30:70, respectively.

Results showed that different fertilizer treatments significantly affected maize growth and kernel yields at all three locations. In the low fertility soil, the OPT treatment produced the highest maize yield followed by the FP and the OPTS. In the medium fertility soil, however, the OPTS produced the highest maize yield followed by the FP and the OPT. There were not much yield differences in the high fertility soil. At all the three experimental locations, the CK treatment produced the lowest maize yield followed by OPT-N, OPT-P and OPT-K. The first year study indicated that NE recommendations can produce 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 followed the order N > P > K.