Evaluation of current fertilization status in walnut orchards of Shangluo District, Shaanxi Province

Objectives For improving nutrient management, determining the optimum baselines of nutrient input in walnut production, the authors have thoroughly evaluated the fertilization behaviors of producers in Shangluo District, one of the walnut main production areas based on a complete survey and field investigation.

Methods More than 511 walnut orchards were investigated and clarified in 2014 and 2016, simultaneously soil samples at 0–20 cm depth were collected in 187 of the 511 orchards. The basic data were used to improve the current fertilizer management and to evaluate the soil fertility in Qinba Mountainous area, Shaanxi Province.

Results The average area of walnut orchard was 0.28 hm² per farmer and the annual total walnut yield was 1245.4 kg/hm² in the area. The N, P₂O₅ and K₂O inputs were (189.1 ± 111.1) kg/hm², (114.8 ± 61.1) kg/hm² and (56.9 ± 72.5) kg/hm² respectively in 2014, and (222.4 ± 115.1) kg/hm², (153.7 ± 80.8) kg/hm², (77.4 ± 91.1) kg/hm² in 2016. Most of the orchards were lack of organic fertilizer input. The soil available N, P and K contents increased as the chemical nutrient input. The soil available P was increased significantly from (16.42 ± 4.50) mg/kg in 2014 to (22.16 ± 4.40) mg/kg in 2016. For the walnut orchard established more than 8 years, the rectified recommended N, P₂O₅ and K₂O input should be (220–270) kg/hm², (110–140) kg/hm² and (150–190) kg/hm² respectively, with the N∶P₂O₅∶K₂O ratio of 1∶0.5∶0. 7 and the organic N input > 77 kg/hm². In 2014 and 2016, there were 15.0% and 22.6% of the orchards in which the N input were reasonable, and 74.5% and 59.5% did not input enough; 39.4% and 33.9% of the orchards were reasonable for P₂O₅ inputs, and 44.0% and 27.3% were not enough, and 16.6% and 38.4% were over applied; there were 8.3% and 13.5% of the orchards whose K₂O inputs were proportional, and as high as 86.2% and 74.5% were not enough; there were 38.7% and 39.2% of the orchards whose organic fertilizer inputs were appropriate, and 61.3% and 60.8% were not enough. Demonstration for nutrient management should be strengthened in this district such as for basal fertilizers, adequate organic manure, while for topdressing, supplementary N in the right time.

Conclusions In general, nitrogen fertilizer should be topdressed in right time in walnut orchards, and potassium fertilizer was heavily inadequate; while phosphorus nutrient was abused recently, and that indicating an environmental risk; compost or manure should be more and wildly used in walnut orchards. Moreover, altering the ammonium bicarbonate into urea or other long-releasing N-fertilizer for basal fertilizer, and more topdressing application as well as some trace nutrients should also be used in the right time.