Oxygation improving soil aeration around tomato root zone in greenhouse

Abstract: Oxygation has shown its great yield potential and wonderful application prospect for the crop growth recently. It can impose aerated water to root zone through subsurface drip irrigation pipe and effectively ameliorate the hypoxic soil environment caused by subsurface drip irrigation. The overall goal of this study was to explore the impacts of oxygation on soil aeration. The specific objective was to determine the relationships among soil oxygen concentration, temperature, air-filled porosity, soil respiration and soil microbial respiration under oxygation conditions. The experiment was conducted in a greenhouse (34o20′N, 108°24′E, Yangling, Shaanxi, China) during the tomato growing season from Aug. 18, 2016 to Jan. 9, 2017. It included 4 treatments, consisting of 2 irrigation managements (the oxygation (O) and subsurface drip irrigation (S)) and 2 irrigation levels (the crop-pan coefficient being 0.6 (W1) and 1.0 (W2)), with 3 replications for each treatment during the whole growing season. No-aerated subsurface drip irrigation was used as control (W1S and W2S) in order to assess the benefits of oxygation (W2O and W1O) on soil aeration. In the experiment, the diurnal variations of soil oxygen concentration, soil temperature and soil respiration were monitored through bi-hourly or hourly measurements, and then average, daily values of soil respiration, oxygen concentration and temperature were calculated from these diurnal measurements. Meanwhile, seasonal variations of air-filled porosity and soil microbial respiration were measured, and then plant root respiration was calculated by soil respiration minus soil microbial respiration. The results showed that soil microbial respiration with oxygation increased by 11.5% significantly (P<0.05) compared with no aerated subsurface drip irrigation conditions. Oxygation also improved soil oxygen concentration and plant root respiration. Especially, the plant root respiration with W2O treatment increased by 38.8% significantly (P<0.05) compared with W2S treatment. Thus, according to controlling the soil water and air coordination, oxygation could promote soil respiration, plant root respiration and then improve soil aeration effectively. What's more, compared with no-aeration (W1S and W2S) and oxygation had a more noticeable impacts on soil respiration and plant root respiration. On the other hand, soil temperature had an effect on soil oxygen consumption through affecting soil respiration. Therefore, soil temperature and soil oxygen concentration were significantly negatively correlated (P<0.01) and the diurnal variation of soil temperature showed an opposite trend with soil oxygen concentration. When the air-filled porosity was small at the tomato pre-growth (seedling to early fruiting stage) period, soil respiration were significantly positive correlated with air-filled porosity and soil oxygen concentration, and negative correlated with soil temperature (P<0.05). When the air-filled porosity maintained stability at the tomato late fruiting and maturation stage, the soil respiration and microbial respiration were significantly positive correlated with soil temperature, and negative correlated with soil oxygen concentration (P<0.05). Meanwhile, there was no significant correlation between air-filled porosity and soil respiration or soil microbial respiration at the tomato late fruiting and maturation stage. Therefore, soil temperature, oxygen concentration and air-filled porosity were important factors that influencing soil respiration and soil microbial respiration during the whole growing season. Oxygation could improve soil aeration effectively, and then decrease the limiting factors of soil respiration, which may be the reason of the greater soil respiration, microbial respiration and plant root respiration. In a word, with higher soil oxygen concentration in the condition of oxygation, soil environment were more preferably for soil respiration (including soil microbial respiration and plant root respiration). In turn, the effectively enhanced soil respiration was also as an indicator of more favorable growing conditions and reduced hypoxic conditions for oxygation.