Selection of green manure varieties and effects of grass management modes on soil fertility in kiwifruit orchards

Abstract: 【Objective】As a clean organic manure source, green manure can effectively improve the soil microbial environment, increase soil organic carbon, and enhance soil carbon sink function, which is of great significance to the sustainability of soil productivity and soil carbon cycle. Intercropping green manure in orchards has become an effective method for soil improvement and restoration, which is an important technical measure to protect the ecological environment of farmland, ensure the quality of agricultural products, reduce fertilizer application, and promote sustainable agricultural development. The effect of green manure on soil habitat was controlled by the types of green manure and orchard cli-mate. In order to provide a theoretical basis for the green production of kiwifruit, the impact of grass management mode on soil nutrients was studied and the suitable leguminous green manure crops were screened for planting in kiwifruit orchards in Hanzhong area.【Methods】The variety selection experiment was conducted to study the characteristics of fresh grass yield and water content changes during the florescence period of green manure crops, including Vicia villosa (VR), Astragalus sinicus (AS), Vicia sativa (VS), Orychophragmus violaceus (OV) and Lathyrus cicera (LC). The orchard grass management modes were set as the following three treatments: annual clean tillage (CK); natural grass (NG) and Vicia villosa + natural grass (VG), and the changes in soil nutrients under different orchard grass management modes were studied.【Results】(1) During the florescence stage of green manure crops, the yield of fresh and dry grass showed as follows: LC＞VR＞VS＞AS＞OV. Among them, LC had the highest yield of fresh grass at 67 332 kg·hm^-2 , followed by VR at 65 499 kg·hm-2 , and there was no significant difference, but they were higher than VS, AS and OV, with an increase of 21.0%-112.5%. LC had the highest hay yield of 11 618 kg·hm^-2 , significantly higher than other green manure varieties, with an increase of 40.5% and 58.4%, respectively, compared with VR and VS. The hay yields of VR and VS were 8270 and 7333 kg·hm^-2 , respectively, significantly higher than those of OV and AS. (2) The total nitrogen content of green manure and fresh grass was as follows: VR＞VS＞LC＞OV＞AS. Among them, the N content of VR reached 39.04 g · kg^-1 , followed by VS 36.07 g · kg^-1 , and they were significantly higher than that of LC, OV, and AS; The N accumulation of VR (323.33 kg · hm^-2 ), LC (308.52 kg · hm^-2 ), and VS (268.31 kg·hm^-2 ) was 87.9%-226.8% significantly higher than that of OV and AS (p＜0.05). The P2O5 content of green manure and fresh grass were mainly manifested as follows: VR＞ AS＞LC＞VS＞OV. Among them, the P2O5 content in VR was 9.05 g · kg^-1 , which was 18.6%-48.8% higher than that in LC, VS, and OV (p＜0.05). The P2O5 content of AS was 8.67 g·kg^-1 , which was 42.6% higher than that of OV (p＜0.05). The accumulation of P2O5 in VR (75.08 kg · hm^-2 ) and LC (72.94 kg·hm^-2 ) was 33.4%-124.4% higher than that of other green manure varieties (p＜0.05). The total potassium contents of green manure fresh grass were mainly manifested as follows: VR＞AS＞VS＞ LC＞OV. The total potassium content of VR was the highest (34.70 g·kg^-1 ), which was 9.4%-68.1% higher than that of VS, LC and OV. The total accumulation of K2O in VR (288.04 kg·hm^-2 ) was 26.3%- 125.5% higher than that of other green manure varieties. LC had the second highest total K2O accumulation (228.03 kg·hm^-2 ), which was 33.0%, 56.9% and 99.8% higher than VS, AS and OV, respectively. (3) Compared with CK, VG significantly increased the content of soil organic matter, available nitrogen, available phosphorus, and available potassium in the 0-60 cm soil layer. Compared with NG, VG can increase the content of soil available nitrogen and organic matter in 0-60 cm soil layer, available phosphorus in 0-20 cm soil layer, and available potassium in 0-40 cm soil layer. Compared with CK, VG increased soil alkaline nitrogen by 144.5%, 145.4% and 453.8% in 0-20, 20-40 and 40-60 cm soil layer, soil available phosphorus by 51.7% , 129.7% and 69.3% , soil available potassium by 129.7% , 68.3% and 121.8%, and soil organic carbon by 108.4%, 95.1% and 122.5%, respectively. Compared with NG, VG increased soil alkaline nitrogen by 12.2%, 17.4% and 178.0%, soil available phosphorus by 21.8%, 21.2% and 20.4%, soil available potassium by 30.4% and 16.4%, and soil organic carbon by 23.1%, 36.3% and 48.9% at 0-20, 20-40 and 40-60 cm, respectively. The mode of VG had the best effect on soil improvement and fertilization in kiwifruit orchards.【Conclusion】During the florescence period, the content of N, P₂O₅, and K₂O nutrients in the hay and plants of VS was the highest, significantly higher than other leguminous green manures. The hay yield was 8270 kg · hm^-2 , and the accumulated amounts of N, P₂O₅ and K₂O were 323.33, 75.08 and 288.04 kg·hm^-2 , respectively. Due to the highbiomass and N, P₂O₅ and K₂O contents, VG can be used as a suitable grass management mode for kiwifruit orchards. Moreover, it had a good effect on improving soil nutrients in kiwifruit orchards, which was conducive to the sustainable development of kiwifruit production in Hanzhong area.