Effects of interrow grass mulching and fertilization on morphology of fine roots and yield of Chinese chestnut

Abstract: 【Objective】To analyze the effects of interrow grass mulching combined with different fertil- ization treatments on soil physical and chemical properties, root system configuration, nutrient content and productivity in chestnut orchards, Qianxi, Hebei province, where drought, water shortage and problems of unscientific fertilization are serious.【Methods】Eight-year-old trees of Castanea mollissima ‘Yanshanzaofeng’were taken as the research object, and a split zone experiment design was adopted. The main treatment included interrow mulching with grass and clean tillage, and the secondary treat- ments were 4 fertilization treatments including single application of inorganic fertilizer (F), single appli- cation of organic fertilizer (M), combined application of organic fertilizer and inorganic fertilizer (F+M) and no fertilization (CK). In 2019 and 2020, we studied the effect of mulching and fertilization on wa- ter, fertilizer, gas and heat status in the soil, fine root growth, and fine root nutrient content in chestnut orchard. The most suitable soil management model was selected based on fruit productivity.【Results】During the growing period (April-October), the average water contents in the soil layers of 0-20 cm and 20-40 cm were significantly higher in the mulching treatments than those in the clean tillage treat- ment. The average water contents in the soil layers of 0-20 cm and 20-40 cm in the mulched soils were 18.76% and 17.62% higher than those in the cleaned soils, respectively. Interrow mulching in the chest- nut orchard significantly reduced the range of diurnal soil temperature change. The variation range of soil temperature in under interrow mulching in summer and autumn was 1.56 °C and 1.10 °C smaller than that in the clean tillage treatment. Mulching had obvious cooling effect in hot season and helped heat preservation in low temperature seasons. Different fertilization treatments significantly reduced the soil bulk density in 0-40 cm soil layer, increased the total porosity of soil, and reduced soil pH value. The influence of interrow mulching on the 0-20 cm soil layer was greater than on the 20-40 cm soil lay- er. The contents of organic matter and available nutrients in rhizosphere soil of the chestnut orchard were significantly increased by grass mulching and fertilization. Different treatments had a significant impact on the nutrient content in fine roots. The order of N, P and K contents in different treatments were F+M>F>M>CK, and that of organic carbon content was F+M>M>F>CK. The effect of mulching and fertilization on fine roots in the 20-40 cm soil layer was significant. Compared with CK, the fertilization treatments increased the root surface area, root volume, root length density, specific root length and total root length of fine roots. Besides, all the indexes in GC were higher than in CT, and the increments in GC(F+M) and CT(F+M) were the highest. Interrow grass mulching and fertilization di- rectly affected tree roots and indirectly affected the reproductive growth, in this study, the average yield per plant of different fertilization treatments in grass mulching area was significantly higher than that in clear tillage area, and the yield per plant of organic and inorganic fertilizer combined application was the highest, and the increase range of different treatments could reach 4.95%-45.21%. Results of aggre- gated boosted trees analysis showed that the contribution degree of different soil physical and chemical indexes to yield per plant was Avail. N>Avail. K>Avail. P>Soil water content>Temperature>Or- ganic matter>pH>Total porosity>Soil bulk density, among which the contribution rates of available nutrients and soil water content to yield per plant were the highest, being 52.21% and 13.91%, respec- tively.【Conclusion】Based on the comprehensive analysis, it is concluded that the combination of organ- ic fertilizer and inorganic fertilizer is the optimal fertilization mode for chestnut cultivation in Qianxi re- gion, and is recommended for extensive application in production of chestnut.