The following article is part of the Special Issue "Contributions to update the FAO56 Guidelines for Computing Crop Water Requirements Sections" but was inadvertently published in a different issue: "Mulching effects on soil evaporation, crop evapotranspiration and crop coefficients: a review aimed at improved irrigation management"

An understanding of nitrogen processes in a paddy field, characterised by large water flux for irrigation and outflows under continuous irrigation, is required to manage adequate nitrogen inputs and outputs. This study identifies the effect of large water flux, especially high infiltration rate, on nitrogen processes in a paddy field under continuous irrigation. The developed nitrogen process model in this study was applied to two paddy fields having different infiltration rates (216 and 106 mm day− 1 on average), and simulated physicochemical and biological nitrogen processes in ponded water, soil water and soil, including whole water flows as well as organic, and inorganic nitrogen forms. In each field, irrigation was found to be the major nitrogen input (153.2–461.5 kg N ha− 1 year− 1), and nitrogen outflow (65.2–284.3 kg N ha− 1 year− 1) found to be smaller than the input from irrigation. The irrigation water was primarily contaminated by dissolved organic nitrogen (DON) and nitrate. Nitrogen transportation from ponded water to soil water was four times greater under high infiltration condition than under low infiltration condition. High nitrogen transport to the soil layer increased air emission via denitrification and decreased outflows. In particular, DON and ammonium transported to soil water are sources of nitrite and nitrate, and denitrification was five times higher under high infiltration than low infiltration. The results of this study imply that paddy fields with high infiltration rates have a greater possibility of nitrogen removal from paddy water, rather than being a pollutant source for the water environment.

The hydraulic and anti-clogging performance of drip irrigation emitters are crucial factors that determine irrigation quality. Subsurface aerated drip irrigation (SADI) has been shown to enhance plant growth and yield, but further investigation is needed to understand its effects on the hydraulic and anti-clogging performance of drip emitters. Thus, based on hydraulic performance tests, the ow rate of emitters was tested under various design nominal discharges (1.0, 1.35, 2.3 L•h -1 ), working heads (2, 4, 6, 8, 10, 12 m), aeration amounts (0, 0.3, 0.5, 0.7, 0.9 L•min -1 ) and soil depths (0, 15 cm ). In addition, the in uence of nominal discharges (ND), working heads (WH), aeration amounts (AA), and soil depths (SD) on the ow rate as well as the ow index were analyzed. Moreover, the relative discharge of emitters was tested by short-term clogging tests, and the in uence of aeration on the anti-clogging performance of the emitter was analyzed. A three-phase ow simulation method, based on one-phase ow and two-phase ow, was employed to investigate the variations in velocity, gas concentration distribution, particle passing rate, and concentration distribution of particles in the ow channel after aeration. The results demonstrate that the effects of ND, WH, AA and SD on the ow rate of the emitter were extremely signi cant(P < 0.01). The in uence of ND and SD on the ow index was signi cant (P < 0.05), while the in uence of AA on the ow index was not signi cant(P > 0.05). In addition, the negative impact of subsurface out ow on the emitter under high-pressure conditions (10, 12 m) was signi cantly less than that under low-pressure conditions (2, 4 m). After aeration, the number of muddy water irrigation times increased, and the growth rates of high-speed mainstream areas after E1, E2, and E3 are 3%-10%, 20%-46%, and 7%-17%, respectively. The particle passing rates of E1, E2 and E3 increased by 10%, 9% and 4%, respectively. This study can provide a research basis for promoting and using subsurface aerated irrigation.