Major challenge in rice production is to achieve the goal of enhancing both food production and fertilizer use efficiency. Rice growth simulation model, ORYZA (v3) was used in the present study to evaluate the model under continuous flooded (CF) and alternate wetting and drying (AWD) regimes with different fertilizer nitrogen (N) rates with different N splits using a historical data of past 45 years. The model satisfactorily simulated crop biomass and nitrogen uptake at both irrigation regimes and fertilizers N rates and splits. The yield differences among the years were large due to climate change, but enhanced by N rates. The response of N curves was different at both water regimes. At 0 N rate, the slope for agronomic efficiency (AE) was high which tends to decrease with increase in N rates. With the one split basal application of N, lowest yield was found with high physiological efficiencies (PE), lowest fertilizer recoveries (RE) and lowest agronomic efficiency (AE). For both water applications and fertilizer levels, high yield with high nitrogen uptake, AE, RE and partial factor productivity (PFP) were witnessed high at four split (3:3:3:1), while having low physiological efficiency. The water productivity (irrigation + rainfall) WP_I+R at basal in one N split for AWD at 150 kg N ha⁻¹ was 1.19 kg m⁻³ and for CF was 0.82 kg m⁻³, whereas for 225 kg N ha⁻¹ WP_I+R of AWD was 1.50 kg m⁻³ and 1.14 kg m⁻³ for CF. In general, AWD exhibited high WP_I+R with no rice yield penalty compared to CF. Splitting with the proper amount of fertilizer N resulted in good water productivity and nitrogen efficiencies, could lead to high rice yield.

Rainfall occurs frequently in South China and results in recurring of drainage/discharge of nitrogen and phosphorus-rich water from paddy fields, which may cause serious non-point source pollution of receiving waters such as rivers. Moreover, time intervals between individual rainfall events are short (often only several days). Thus, not only is the treatment of discharge water needed, but a more rapid form of treatment is desired as well. On the basis of the literature, constructed wetlands could remove nitrogen and phosphorous from paddy field drainage/outflow, and effective microorganisms (EM) could also be added to enhance the removals. A field experiment was conducted to demonstrate the wetland effectiveness and EM enhancement. The experiment was conducted from June to October in 2016. By applying EM to constructed wetlands, after 8 days, concentrations of total nitrogen (TN), ammonium nitrogen (${\mathrm{NH}}_4^{ +}$-N), nitrate nitrogen (${\mathrm{NO}}_3^{ -}$-N), and total phosphorus (TP) were reduced by 88%, 91%, 89%, and 50%, respectively. Within the first 4 days, TN and TP concentrations were reduced by 78% and 40%, respectively, with EM application, in comparison to 50% and 20%, respectively, without EM application, representing additional respective reductions of 28% and 20% by applying EM. The results from the field experiment indicated a significant improvement of phosphorus and nitrogen removals by applying effective microorganisms.

Agricultural practices such as water and N management can contribute to greenhouse gas (GHG) emissions. Fertigation frequency and level are the two most important factors of irrigation scheduling. Proper irrigation management can establish moderate moist conditions throughout the crop growth period in the root zone and reduce GHG emissions and NH₃ volatilization. The main objective was to evaluate the possibility of reducing soil N₂O and CO₂ emissions and NH₃ volatilization without crop yield reduction by manipulating the subsurface-drip fertigation (SDF) frequency and level. An experiment was carried out adopting three SDF frequencies, High-Frequency (7-day, HF), Medium-Frequency (8-day, MF), and Low-Frequency (10-day fertigation intervals, LF), and two irrigation levels, 80% (I₈₀) and 70% (I₇₀) of amount in farmer’s common practice (1500 m³ ha⁻¹). Urea, N > 46.2% at the rate of 90% of traditional fertilization level (270 Kg N ha⁻¹) was injected with irrigation water. Results indicated that soil N₂O, CO₂, NO₃⁻-N, NO₂⁻-N, and water-filled pore space increased with fertigation frequency and an opposite pattern for NH₄⁺-N and NH₃. HF significantly (p < 0.05) increased crop yield by 45.1% and 49.2% compared to LF, under I₈₀ and I₇₀ levels, respectively. At the same irrigation level, HF was the optimum management practice. Person correlation analysis showed significant correlations between NO₂⁻-N and N₂O, CO₂ and soil temperature, and NH₄⁺-N and NH₃. The study suggests that HF of SDF with emitters buried at 0.15 m depth helps to keep high Chinese cabbage yield increases GHG emissions, but is not significant, and decreases NH₃ volatilization.

Irrigation using marginal quality water (brackish, saline, or treated wastewater, with a salinity of 2–8 g L⁻¹) instead of fresh water alters the soil carbon and nitrogen cycle, and thus, soil greenhouse gas emissions. To reveal the responses of soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions and their global warming potentials (GWPs) to irrigation water salinity, a pot experiment was conducted at three levels (2, 5, and 8 g L⁻¹, namely S2, S5, and S8). The results show that the cumulative soil CO₂ emissions were reduced with increases in the irrigation water salinity and were 11.6–28.1% lower than those from the fresh water-irrigated treatment (CK). The cumulative N₂O emissions from S2 and S8 decreased by 22.7% and 39.6% (p < 0.05), respectively, in comparison to CK, whereas those from S5 increased by 87.7% (p < 0.05). The cumulative GWPs from S2 and S8 were 19.6% and 44.1% lower than those from CK, while those from S5 were significantly higher (p < 0.05). These findings indicate that reducing the salinity of brackish water from 5 to 2 g L⁻¹ before using it for irrigation is a potential strategy to mitigate soil GHGs and solve water resource scarcity. The response of soil greenhouse gas (GHG) emissions to salinity may be significantly different among irrigation water salinity ranges. The results have an important guiding significance for exploring greenhouse gas emission reduction measures, and sustainable utilization models of water and soil resources.

Agricultural practices, such as applying excessive water and nitrogen fertilizer to increase the crop yield, can be a significant source of greenhouse gas emissions (GHGs). Therefore, techniques and proper management are needed to mitigate these emissions without yield reduction. The experiment used three subsurface drip irrigation (SDI) depths with emitters buried at 0.05, 0.10, and 0.15 m below the soil surface, along with two nitrogen fertilizer (Urea, N > 46.2%) application levels of 300 kg N ha⁻¹ (N₃₀₀) and 240 kg N ha⁻¹ (N₂₄₀) to investigate the effect of vertical and horizontal water and fertilizer distribution on N₂O emissions under different SDI techniques in greenhouse conditions. The results indicated that soil N₂O emissions from SDI₁₀ and SDI₁₅ decreased by 7.06% and 10.69%, respectively, compared to SDI₅. N₂O, WFPS, NH₄⁺-N, and NO₃⁻-N were significantly reduced with the increased radial distance from the emitter. N₂O was positively correlated to WFPS and NH₄⁺-N while negatively correlated to NO₃⁻-N. The NH₄⁺-N and NO₃⁻-N concentrations decreased with depth and increased with fertilization events. Furthermore, N₂O, WFPS, NH₄⁺-N, and NO₃⁻-N were increased under N₃₀₀ compared to N₂₄₀ (p > 0.05). The findings demonstrated that the Chinese cabbage yield was significantly enhanced under SDI₁₅ compared to SDI₅ and SDI₁₀. Furthermore, N₃₀₀ can increase the cabbage yield more than N₂₄₀ among all treatments.