Aerated subsurface drip irrigation improving soil aeration and tomato growth

Abstract: Effects of aerated subsurface drip irrigation (ASDI) on yield potential and quality of crop, and relationships between soil aeration, crop yield and fruit quality are less known so far. In order to reveal the relationship between crop growth and soil aeration under ASDI, a pot experiment was conducted using tomato in the Efficiency Agriculture Water Experimental Farm of North China University of Water Resources and Electric Power (34°47′5.91″N, 113°47′20.15″E). Herein, 2 levels of irrigation amount (W1 and W2 as 0.6 and 1.0 times of the crop-pan coefficient, respectively) and 2 aeration treatments (A and C as ASDI and control treatment, i.e., non-aeration treatment by subsurface drip irrigation) were set up. During the trial, the soil aeration index under a loamy clay soil, such as air-filled porosity, soil dissolved oxygen (DO), oxidation-reduction potential (Eh), oxygen diffusion rate (ODR), soil respiration, photosynthesis index, crop aboveground biomass, root biomass, nutrient uptake, yield and fruit quality were monitored systematically. The correlation analysis was conducted among soil aeration index, photosynthesis index, nutrient uptake efficiency, yield, and fruit quality. Results showed that the ASDI improved the soil aeration. Compared to control treatment groups, the DO in W2A and W1A treatments were increased by 25.71% and 10.64% on the next day after irrigation at flowering and fruit bearing period (P<0.05). In W2A and W1A, similarly, the ODR were increased by 52.90% and 32.27% and the Eh were increased by 41.99% and 20.99%, respectively (P<0.05). In contrast with the control groups, the soil respiration in W2A and W1A were significantly increased by 64.70% and 28.45% during the flowering and fruit bearing period, 14.17% and 33.24% during the fruit expanding period, 56.91% and 32.86% during the mature period (P<0.05). Meanwhile, there were obvious positive correlations between ODR and Eh and DO and air-filled porosity (P<0.01). The ASDI had a positive effect on the crop photosynthesis, benefiting the increment in biomass, nutrient uptake and crop quality. Compared to the control groups, the net photosynthetic rate in W2A treatment at flowering and fruit bearing period, fruit expanding period and mature period were increased by 14.51%, 21.72% and 13.76%, respectively (P<0.05). The net photosynthetic rate in W1A treatment at fruit expanding period was increased by 55.26% (P<0.05). The aboveground fresh weight and root fresh weight significantly increased by 68.14% and 55.18% in W2A treatment, while the aboveground fresh weight and root fresh weight increased by 9.88% and 45.37% in W1A treatment (P<0.05). Compared to the control treatment, nitrogen uptake in root, stem and leaf were increased by 52.94%, 42.03% and 24.12%, and phosphorus utilization in root and stem were increased by 74.07% and 36.00%, while the potassium accumulation in root, stem and leaf were increased by 56.52%, 41.09% and 22.44% in W2A treatment (P<0.05). Similarly, the crop yield, fruit soluble solids, vitamin C content, total acid content and soluble protein in W2A were increased by 66.40%, 51.77%, 20.26%, 55.26% and 63.64%, respectively (P<0.05). The fruit soluble solids, vitamin C content and total acid content in W1A treatment were increased by 43.55%, 29.68% and 71.43%, respectively (P<0.05). The ASDI treatment at the irrigation of 1.0 times of the crop-pan coefficient showed the most efficient promotion on soil aeration, crop growth and fruit quality enhancement. There were significantly positive correlations between crop yield and DO, Eh and respiration under ASDI (P<0.05). In addition, there were positive correlations between crop quality (soluble solids and total acid content) and soil aeration indexes (DO, ODR and respiration) (P<0.05). In sum, these results would provide valuable information for the effect of ASDI on soil aeration, crop yield and fruit quality enhancement.