Objective There are many kinds of soil and water conservation measures of orchards at present, but the effects of diverse soil and water conservation measures are different among regions. Most of the studies were current situation and short-term effects of soil and water conservation after taking measures. Therefore, the soil and water conservation effects of terrace and grass growing on slope orchards in the red soil hilly area needed to be further studied.

Method In this study, loquat (Eriobotrya japonica (Thunb.) Lindl) orchards which was 20-year old with different engineering measures (slope and terrace) and biological measures (clear ploughing and grass growing, chose Paspalum notatum Flugge as grass-growing variety) in the typical red soil hilly region were selected to be the research object. Three mixed soil samples were respectively collected from upper, middle and lower slope position in the experimental area. Difference of the migration characteristics and contents of available and total nutrients in orchard soil as well as the fruit yield under different measures were analyzed, the principal component analysis was carried out, and the comprehensive effects of different soil and water conservation measures were calculated.

Result ①The distribution characteristics of soil nutrients in slope orchards were significantly different due to different measures, and both terrace and grass growing measures could effectively reduce the migration of soil nutrients on the slope. The terrace measures reduced the migration of soil organic matter, available nitrogen and available potassium between slopes by 49.5%, 24.7% and 46.6%, respectively. Grass growing measures could reduce the transfer of soil organic matter, available nitrogen and available potassium between slopes by 59.9%, 81.9% and 8.4%, respectively. ② Terrace and grass growing measures were beneficial to the accumulation of soil organic matter and the improvement of nitrogen and potassium nutrients. The average increase of soil organic matter, available nitrogen and total phosphorus content by terrace measures was 23.0%, 6.5% and 38.6%, while the average increase of soil organic matter, available nitrogen and available potassium content by grass growing measures was 41.4%, 38.5% and 28.5%. And among these, the orchard with terrace-grass growing had the highest soil pH value, and it had the most significant effect on alleviating soil acidity. Meanwhile, soil organic matter, available nitrogen, total phosphorus and total potassium contents were the highest in the orchard with terrace-grass growing measures as well. ③ Grass growing measures significantly increased fruit yield, and the average yield of terraced-grass growing orchard was the highest, with an average yield of 13.5 kg per plant, which was 36.0%, 6.5% and 27.5% higher than that of clear ploughing along the slope, grass growing along the slope and clear ploughing of terrace orchards, respectively.

Conclusion In conclusion, the terraced combined with grass growing orchards can reduce nutrient migration, which is conducive to the maintenance of soil organic matter and nutrients on slope land, and is the optimal garden construction model in red soil hilly areas.