Effects of intercropping with green manures on soil nutrients and traits of Xinxin 2 walnut

Abstract:【Objective】The effects of different green manure intercropping and overturning treatments on soil nutrients and traits of Xinxin 2 walnut were studied in order to establish suitable green manure intercropping pattern for improving walnut quality, orchard soil fertility and orchard ecological environ-ment.【Methods】Three green manure plants, rape, pea and Chinese milk vetch, were interplanted between rows of Xinxin 2 walnut trees. They were turned over at initial blooming or full blooming stage. 30 days and 60 days after turning over, soil nutrient contents were determined. In August, the leaf traits of Xinxin 2 walnut under different treatments were determined, and the character and quality of mature fruit were tested at the end of September.【Results】The results showed that the change pattern of soil nutrient content was different under different green manure intercropping and overturning treatments. At 30 d after overturning, intercropping with all the three manure plants increased the contents of soil organic matter, total nitrogen, hydrolytic nitrogen and total potassium initially, but decreased them in later periods, and finally caused a lower nutrient level than before green manure sowing. The soil organic matter content increased by 0.40 g·kg^-1, 0.30 g·kg^-1 and 0.10 g·kg^-1 by intercropping with rape, pea and Chinese milk vetch, respectively; hydrolytic nitrogen by 7.60 mg·kg^-1, 17.80 mg·kg^-1 and 15.30 mg·kg^-1, respectively; and total potassium content by 3.50 g · kg^{- 1}, 1.30 g · kg^{- 1} and 0.60 g · kg^{- 1}, respectively. 60 days after pea green manure was overturned, the pH of the soil increased and became higher than that in the rest treatments, but pH only increased by 0.16.30 days after rape, pea and Chinese milk vetch were overturned, the total value of soil nutrient content increased significantly by 3.88 g·kg^-1, 1.69 g·kg^-1 and 0.83 g·kg^-1, respectively. However in CK, it decreased by1.31 g·kg^-1. Among the three green manure in-tercropping modes, there were no significant differences in leaf area and perimeter. The leaf area was 5.29% and 4.88% higher than CK in rape and Chinese milk vetch intercropping, respectively. The hundred-leaf fresh weight and dry weight of Xinxin 2 walnut reached 340.64 g and 115.12 g under pea intercropping, respectively, which were 13.07% and 20.71% higher than CK, respectively, and significantly higher than those in the other treatments. There was no significant difference in the dry-fresh ratio of walnut leaves among different treatments, which was between 0.32 and 0.34. The nutrient content of leaf showed significant differences among different green manure intercropping. The leaf N content under pea and rape intercropping was 26.00 g · kg^{- 1} and 25.80 g · kg^{- 1}, respectively and highest among all treatments. There was no significant difference between the two treatments. The leaf P content under rape intercropping was 2.46 g · kg^-1, which was 59.74% higher than that of CK and significantly higher than in pea and Chinese milk vetch intercropping. The leaf K content under pea, rape and Chinese milk vetch treatment was significantly higher than that in CK, and increased by 43.62% , 29.79% and 23.40%, respectively. The chlorophyll content of Xinxin 2 leaves reached 53.74 under pea intercropping treatment, 6.00% higher than CK. It was higher than CK and intercropping with rape or Chinese milk vetch. The longitudinal and transverse diameters of Xinxin 2 walnut fruits showed no significant difference among the four treatments. However, pea intercropping could significantly increase fruit lateral diameter by 1.91% (34.13 cm), significantly higher than the other treatments. Both pea and rape treatments could significantly improve the single fruit quality of Xinxin 2 walnut, they were 17.13% and 11.80% higher than CK, respectively. The kernel weight reached 7.38 g under pea intercropping, which was significantly higher than that in the other treatments. The shell thickness of Xinxin 2 walnut was 1.33 mm and 1.29 mm under pea and rape intercropping treatments, respectively. There were 27.88% and 24.04% higher than CK, respectively. The protein content of Xinxin 2 fruit was not significantly different between pea and rape intercropping, which had a protein content of 193.00 g·kg-1 and 192.00 g·kg^-1, respectively. The fat content of Xinxin 2 fruit reached 653.00 g · kg^{- 1} and 652.00 g · kg^{- 1}under Chinese milk vetch and rape intercropping, respectively. They were 2.35% and 2.19% higher than CK, respectively, and also significantly higher than pea intercropping treatment.【Conclusion】According to the ac-cumulation of nutrients in the soil after each green manure treatment, as well as leaf traits, nutrient con-tent, and fruit quality traits, intercropping with pea is the best, followed in order by rape and Chinese milk vetch for Xinxin 2 walnut orchard. Key words: Walnut; Xinxin 2; Green manure; Soil nutrients; Fruit quality