Changes in dissolved oxygen concentration in an aerated drip irrigation system under different drip emitters

The drip emitter type used influences the dissolved oxygen concentration (DOC) distribution in a drip irrigation system. Understanding the spatial and temporal DOC distribution in the irrigation system and its change pattern and determining the optimal irrigation emitter and aeration concentration threshold are important to reasonably apply aerated irrigation. Here, we designed three common drip irrigation emitter treatments under a drip irrigation system, i.e., an inserted in-line labyrinth emitter with a flow rate of 1.0 L h−1 (T1) and 2.2 L h−1 (T2), respectively, and a pressure-compensating emitter with a flow rate of 2.0 L h−1 (T3). Each irrigation emitter was associated with five initial DOC treatments, i.e., 3–5 mg L−1 (CK), 10 mg L−1 (C1), 15 mg L−1 (C2), 20 mg L−1 (C3), and 25 mg L−1 (C4). The results showed that the DOC values gradually increased in nonaerated water (CK) but gradually decreased in aerated water with standing time. Each emitter type significantly increased the DOC values after nonaerated water (CK) passed through different drip irrigation systems, and the highest increase (73.7%) was observed in the T1CK treatment. However, the DOC values significantly decreased after the aerated water passed through the drip irrigation systems, especially in the T2 treatment (33.2%). In addition, the reduction (or increase) in DOC in aerated water (or nonaerated water) in the first 10 m of the capillary pipe was smaller than that in the last 10 m for all treatments except T1C1. Furthermore, the T3 treatment had the most stable attenuation at different initial DOC treatments, with a maximum laying length of 20 m. More importantly, aeration can significantly increase DOC in the soil water (DOS), and the maximum value occurred when the initial DOC was 19.8 mg L−1. Hence, for practical application, the recommended initial DOC range for aerated irrigation is 15 ~ 20 mg L−1 combined with a pressure-compensating emitter at a flow rate of 2.0 L h−1 (T3). This study provides technical support for the optimal design and rational application of aerated drip irrigation systems.