Benefit evaluation on typical soil and water conservation measures in citrus orchard on red soil slope

Abstract: In recent years, unreasonable development of sloping orchard land has resulted in many problems such as soil erosion, soil degradation, non-point source pollution, etc. Thus, it is necessary to study the comprehensive benefits of different soil and water conservation measures for orchards on red soil slopeland, which provides technical reference for orchard development and management. Studies about the relationships between runoff, sediment reduction, nutrient losses and soil physicochemical properties under soil and water conservation measures have been fully reported. However, most of the studies were conducted under a single soil and water conservation measure. It has been rarely reported about the comprehensive comparisons of plant measures, tillage measures, engineering + plant measures and engineering measures. Long term in situ observation in the standard citrus orchard plots was carried out to investigate the runoff, sediment and nutrient losses under different plant measures, cultivation measures and engineering measures and their effects on the soil physical and chemical properties. Six standard runoff plots with same slopes were selected as experimental plots. The sizes of the plots were 5 m (width) × 20 m (length). The horizontal projection areas and slopes of the plots were 100 m2 and 12°, respectively. Three rectangular pools were built in each plot. Twelve citrus trees were planted in each plot. A plot was selected as the control plot with planted citrus trees only. Different plant measures, tillage measures, engineering+plant measures and engineering measures were adopted in the other five plots. The average annual runoff reduction benefits of different measures were ranked in the order: plant measures > engineering + plant measures > tillage measures> engineering measures. But the average annual sediment reduction benefit was slightly different, which were ranked in the order: engineering + plant measures > plant measures > tillage measures > engineering measures. The average annual runoff reduction (71.43%) of plant measures was the highest. But the sediment reduction benefit (95.88%) of engineering+plant measures was the highest. The average annual nitrogen reduction benefits were ranked in the order: plant measures > tillage measures> engineering+plant measures> engineering measures. The phosphorus reduction benefits were similar with the sediment reduction. Plant measures had the lowest nitrogen losses, the reduction rates were 19.84%. Engineering+plant measures had lowest phosphorus losses, the reduction rates were 68.94%. The soil field water-holding capacity decreased in the order: tillage measures > plant measures > engineering+plant measures> engineering measures. The soil field water-holding capacity of tillage measures and plant measures were 14.60% and 7.19 % higher than that of control plot, respectively. The variation trends of soil physical and chemical indicators under different soil and water conservation measures were slightly different. Soil moisture content and WSA were the highest in plant measures, which were 18.94% and 4.42% higher than the control plot. Soil nutrients were most improved by the plant measures. In all plant measures, the increase rates of soil nutrient for the citrus plot with whole coverage of Paspalum notatum were the highest, with the organic matter increasing by 34.53%, total nitrogen increasing by 78.26% and total phosphorus increasing by 12.24%, respectively. Thus, the plant measures performed the best in the soil and water conservation benefits, for example, reduction of sediment, nutrient loss and soil improvement. The results could offer theoretical reference for soil and water conservation control measures selection, soil quality improvement and solving of soil erosion and environmental problems suitable in the development of orchard in hilly red soil region of southern China.