Construction and validation of apple Nutrient Expert system based on yield response and agronomic efficiency

Objectives To develop an alternative for optimum fertilization in apple production systems, Nutrient Expert (NE) for apple fertilization based on yield response (YR) and agronomic efficiency (AE) was established, and its practicability was evaluated simultaneously using field experiments.

Methods We collected the published results from 272 field experiments and calculated the data of several parameters such as YR, internal efficiency and AE from 2002 to 2017. The nutrient uptake of N, P, and K in apple was estimated by QUEFTS model, and NE was established based on YR and AE. Two-year field experiments (2017–2019) treated with NE, FP (farmers’ practice, FP), and ST (soil test, ST) were carried out in Luochuan and Changwu counties of Shaanxi Province, and Yuncheng county of Shanxi Province, and four apple orchards were selected in each county to investigate apple yield, nitrogen use efficiency (NUE), and economic benefits in response to NE, FP, and ST treatments.

Results The averaged apple yield was 33.91 kg/hm². The averaged N, P, and K concentrations were 3.19, 0.57, and 8.07 g/kg in apple fruit, 7.57, 1.12, and 4.61 g/kg in branches, and 24.02, 1.38, and 8.58 g/kg in leaves, respectively. The averaged N, P, and K uptakes in aboveground parts (i.e., fruit, branches, and leaves) were 89.06, 11.11, and 83.32 kg/hm², and the harvest indices were 0.19 kg/kg for N, 0.27 kg/kg for P, and 0.48 kg/kg for K, respectively. The QUEFTS model indicated that nutrient uptake was linearly increased when apple yield reached 50%–60% of potential yield, and N 3.1 kg, P 0.4 kg, and K 2.9 kg were required to produce 1 t apple fruit, with a N: P: K ratio of 7.8:1.0:7.3. The yield response for N, P, and K was quadratically correlated with their respective AE, and the corresponding equation was AE_N=−0.0054YR_N²+1.767YR_N−0.056 (R²=0.804, n=270) for N, AE_P=−0.0053YR_P²+2.775YR_P+0.538 (R²=0.763, n=257) for P, and AE_K=−0.0036YR_K²+1.629YR_K+1.653 (R²=0.794, n=264) for K, respectively. The field experiment results revealed that the NE treatment substantially decreased the application rates of N-P-K fertilizers by 41.9%, 37.0%, and 43.6%, respectively. More importantly, apple yield, AE_N, PFP_N and economic benefit in NE were increased by 17.3%, 81.7%, 80.6%, and 21.9%, respectively, compared to the FP. Relative to the ST, the N-P-K fertilizers in NE were decreased by 20.8%, 25.0%, and 29.7%, respectively, while apple yield, AE_N, PFP_N, and economic benefits were comparable to that of ST.

Conclusions Apple Nutrient Expert system based on yield response and agronomic efficiency was developed using QUEFTS model. Field experiments indicated that the apple Nutrient Expert system was a potentially multi-win strategy for optimizing apple fertilization, enhancing apple yield, and increasing NUE and economic benefits.