To ameliorate soil oxygen deficiencies around subsurface drip irrigation (SDI) drippers, aerated irrigation (AI) was introduced to supply aerated water to the soil through venturi installed in the SDI pipeline.  The objectives of this study were to assess the effects of AI on soil respiration (SR), air-filled porosity (AFP), soil temperature (ST), and oxygen concentrations (OCC).  Total soil respiration (TSR), biological activity temperature index (BAT), and soil oxygen consumption (OCS) based on SR, ST, and OCC, respectively, were subsequently calculated to explore the relationships between TSR, BAT, OCS, OCC, and AFP.  Greenhouse-based experiments included two treatments: AI and unaerated SDI (CK), during the tomato growing season in the fall of 2015.  The results showed that compared with CK, AI treatment significantly increased OCC and AFP (by 16 and 7.4%, respectively), as well as TSR and OCS (by 24.21 and 22.91%, respectively) (P<0.05).  Mean fruit yield with AI treatment was also 23% higher (P<0.05) than that with CK.  When BAT was controlled, partial correlations between TSR, OCS, OCC, and AFP were all significant in the AI treatment but not in the CK treatment.  TSR was more sensitive to the interaction effects of OCC, OCS, AFP, and BAT under the AI treatment.  Thus, the significantly increased TSR with AI appeared to be due to the favorable soil aeration conditi ons (higher OCC and AFP).  Furthermore, the improvements in soil aeration conditions and respiration with AI appeared to facilitate the improvement in fruit yields, which also suggests the economic benefits of AI.

Excessive use of nitrogen (N) fertilizers in agricultural systems increases the cost of production and risk of environmental pollution.  Therefore, determination of optimum N requirements for plant growth is necessary.  Previous studies mostly established critical N dilution curves based on aboveground dry matter (DM) or leaf dry matter (LDM) and stem dry matter (SDM), to diagnose the N nutrition status of the whole plant.  As these methods are time consuming, we investigated the more rapidly determined leaf area index (LAI) method to establish the critical nitrogen (N_c) dilution curve, and the curve was used to diagnose plant N status for winter wheat in Guanzhong Plain in Northwest China.  Field experiments were conducted using four N fertilization levels (0, 105, 210 and 315 kg ha⁻¹) applied to six wheat cultivars in the 2013–2014 and 2014–2015 growing seasons.  LAI, DM, plant N concentration (PNC) and grain yield were determined.  Data points from four cultivars were used for establishing the Nc curve and data points from the remaining two cultivars were used for validating the curve.  The N_c dilution curve was validated for N-limiting and non-N-limiting growth conditions and there was good agreement between estimated and observed values.  The N nutrition index (NNI) ranged from 0.41 to 1.25 and the accumulated plant N deficit (N_and) ranged from 60.38 to –17.92 kg ha⁻¹ during the growing season.  The relative grain yield was significantly affected by NNI and was adequately described with a parabolic function.  The N_c curve based on LAI can be adopted as an alternative and more rapid approach to diagnose plant N status to support N fertilization decisions during the vegetative growth of winter wheat in Guanzhong Plain in Northwest China.