Combined effects of biomaterial amendments and rainwater harvesting on soil moisture, structure and apple roots in a rainfed apple orchard on the Loess Plateau, China

Adequate soil moisture and good soil structure are critical to sustainable productivity of rain-fed apple (Malus pumila Mill) orchards on China?s Loess Plateau. Droughts, poor soil structure, low soil fertility, and a lack of synchronization between plant water demand and rainfall results in low rainfall use efficiency in gentle slope orchards of this area. This study combined soil biomaterial amendment and rainwater harvesting (BARH), and evaluated the effect of BARH on soil moisture content (SMC), soil water storage (SWS), soil saturated hydraulic conductivity, soil structure, and apple roots in a field experiment in rainfed apple orchard on the Loess Plateau from 2016 to 2018. Three treatments: (1) the BARH treatment, combination of biomaterial amendment and rainwater harvesting (2) the RH treatment, rainwater harvesting measure only and (3) the control (CK) treatment, which is the local traditional practice. Compared with the CK treatment, the BARH and RH treatment significantly (P < 0.05) improved SMC by 31.08% and 18.83%, respectively, and SWS by 102.19 mm and 35.30 mm, respectively, within 0-300 cm during the apple growing season (from April to October) over three years. There were notable and significant increases in SMC in the 0-160 cm soil layer. SWC in the autumn improved due to heavy rainfall and lower water consumption by the apple trees. This alleviated the critical water requirements of early spring apple trees for the following year, and therefore, less rainfall was required. The BARH treatment had a soil bulk density (BD) that was 3.52% lower (P < 0.05) within 0-60 cm soil depth, 83.93% higher saturated soil conductivity (Ksat), and 4.9% higher sand-size soil macroaggregates (0.02-2 mm) within 0?40 cm soil depth, compared to the CK treatment over three years. 70% of the root systems were concentrated in the 0-160 cm soil layer in all treatments which was highly correlated with SMC. Root dry weight density (RWD) under BARH and RH treatments increased by 33.35% and 7.52% within 0-300 cm of the soil in comparison to the CK treatment, respectively. Likewise, the root length density (RLD) under BARH and RH treatments increased by 52.16% and 21.34% within the 0-300 cm soil layer compared to the CK treatment, respectively. Therefore, the combination of biomaterial amendment and rainwater harvesting is an effective cultivation measure for sustainable development of rainfed apple orchards on the Loess Plateau.