Gravel mulching plays a vital role in modifying the hydrological cycle in arid and semi-arid areas.Yet,the mechanisms underlying long-term mulching effects on soil evaporation remain poorly understood.To investigate t...Gravel mulching plays a vital role in modifying the hydrological cycle in arid and semi-arid areas.Yet,the mechanisms underlying long-term mulching effects on soil evaporation remain poorly understood.To investigate the hydrological effects of mixed gravel–soil mulching(MGSM),we conducted a controlled 39-d soil evaporation experiment(from 22 July to 30 August 2021)using micro-lysimeters at the field experimental site of Ningxia University,China.The soil evaporation rate(E),cumulative soil evaporation(Ec),soil water content(SWC),mulch resistance(rm),and micro-meteorological variables were assessed for six mulch treatments,each containing a different proportion of gravel by volume:100.00%(M1),80.00%(M2),60.00%(M3),40.00%(M4),20.00%(M5),and 0.00%(M6).The treatments(M2–M6)showed a prolonged soil moisture depletion phase and greater Ec(28.71%–83.31%)relative to the gravel-only treatment(M1)(P<0.050);these effects were primarily attributed to reduced rm.As compared to Ec,the SWC showed an inverse response,decreasing as Cg decreased.A robust exponential relationship was observed between E and rm(P<0.001).Evaporation suppression mediated by rm was particularly pronounced during the residual evaporation stage(>312 h post-wetting),with the strongest effect occurring in M3,where the mean rm doubled.The SWC,mulch properties,and micro-meteorological parameters(i.e.,air relative humidity and surface net radiation flux)were the most important predictors of rm in the mulch treatments.Together,these results suggested that MGSM unexpectedly exacerbated surface soil moisture loss by reducing rm.To mitigate this effect,an optimized mixed gravel–soil mulch,containing 60.00%gravel by volume,might be used;this mixture balances evaporation control with hydrological sustainability and represents a practical strategy for dryland management,offering a compromise between short-term water retention and sustained soil moisture regulation.展开更多
Greenhousing is a technique to bridge season gap in vegetable production and has been widely used worldwide. Calculation of water requirement of crops grown in greenhouse and determination of their irrigation schedule...Greenhousing is a technique to bridge season gap in vegetable production and has been widely used worldwide. Calculation of water requirement of crops grown in greenhouse and determination of their irrigation schedules in arid and semi-arid regions are essential for greenhouse maintenance and have thus attracted increased attention over the past decades. The most common method used in the literature to estimate crop evapotranspiration（ET） is the Penman-Monteith（PM） formula. When applied to greenhouse, however, it often uses canopy resistance instead of surface resistance. It is understood that the surface resistance in greenhouse is the result of a combined effect of canopy restriction and soil-surface restriction to water vapor flow, and the relative dominance of one restriction over another depends on crop canopy. In this paper, we developed a surface resistance model in a way similar to two parallel resistances in an electrical circuit to account for both restrictions. Also, considering that wind speed in greenhouse is normally rather small, we compared three methods available in the literature to calculate the aerodynamic resistance, which are the r_a^1 method proposed by Perrier（1975a, b）, the r_a^2 method proposed by Thom and Oliver（1977）, and the r_a^3 method proposed by Zhang and Lemeu（1992）. We validated the model against ET of tomatoes in a greenhouse measured from sap flow system combined with micro-lysimeter in 2015 and with weighing lysimeter in 2016. The results showed that the proposed surface resistance model improved the accuracy of the PM model, especially when the leaf area index was low and the greenhouse was being irrigated. We also found that the aerodynamic resistance calculated from the r_a^1 and r_a^3 methods is applicable to the greenhouse although the latter is slightly more accurate than the former. The proposed surface resistance model, together with the r_a^3 method for aerodynamic resistance, offers an improved approach to estimate ET in greenhouse using the PM formula.展开更多
基金supported by the National Key Research and Development Program of China(2021YFD1900600)the National Natural Science Foundation of China(52169010,51869023)+1 种基金the Natural Science Foundation Key Project of Ningxia Hui Autonomous Region(2021AAC02008)the First-Class Discipline Construction Project in Hydraulic Engineering of Ningxia University(NXYLXK2021A03).
文摘Gravel mulching plays a vital role in modifying the hydrological cycle in arid and semi-arid areas.Yet,the mechanisms underlying long-term mulching effects on soil evaporation remain poorly understood.To investigate the hydrological effects of mixed gravel–soil mulching(MGSM),we conducted a controlled 39-d soil evaporation experiment(from 22 July to 30 August 2021)using micro-lysimeters at the field experimental site of Ningxia University,China.The soil evaporation rate(E),cumulative soil evaporation(Ec),soil water content(SWC),mulch resistance(rm),and micro-meteorological variables were assessed for six mulch treatments,each containing a different proportion of gravel by volume:100.00%(M1),80.00%(M2),60.00%(M3),40.00%(M4),20.00%(M5),and 0.00%(M6).The treatments(M2–M6)showed a prolonged soil moisture depletion phase and greater Ec(28.71%–83.31%)relative to the gravel-only treatment(M1)(P<0.050);these effects were primarily attributed to reduced rm.As compared to Ec,the SWC showed an inverse response,decreasing as Cg decreased.A robust exponential relationship was observed between E and rm(P<0.001).Evaporation suppression mediated by rm was particularly pronounced during the residual evaporation stage(>312 h post-wetting),with the strongest effect occurring in M3,where the mean rm doubled.The SWC,mulch properties,and micro-meteorological parameters(i.e.,air relative humidity and surface net radiation flux)were the most important predictors of rm in the mulch treatments.Together,these results suggested that MGSM unexpectedly exacerbated surface soil moisture loss by reducing rm.To mitigate this effect,an optimized mixed gravel–soil mulch,containing 60.00%gravel by volume,might be used;this mixture balances evaporation control with hydrological sustainability and represents a practical strategy for dryland management,offering a compromise between short-term water retention and sustained soil moisture regulation.
基金funded by the Science and Technology Innovation Project of Chinese Academy of Agricultural Sciences(FIRI2016-07)
文摘Greenhousing is a technique to bridge season gap in vegetable production and has been widely used worldwide. Calculation of water requirement of crops grown in greenhouse and determination of their irrigation schedules in arid and semi-arid regions are essential for greenhouse maintenance and have thus attracted increased attention over the past decades. The most common method used in the literature to estimate crop evapotranspiration（ET） is the Penman-Monteith（PM） formula. When applied to greenhouse, however, it often uses canopy resistance instead of surface resistance. It is understood that the surface resistance in greenhouse is the result of a combined effect of canopy restriction and soil-surface restriction to water vapor flow, and the relative dominance of one restriction over another depends on crop canopy. In this paper, we developed a surface resistance model in a way similar to two parallel resistances in an electrical circuit to account for both restrictions. Also, considering that wind speed in greenhouse is normally rather small, we compared three methods available in the literature to calculate the aerodynamic resistance, which are the r_a^1 method proposed by Perrier（1975a, b）, the r_a^2 method proposed by Thom and Oliver（1977）, and the r_a^3 method proposed by Zhang and Lemeu（1992）. We validated the model against ET of tomatoes in a greenhouse measured from sap flow system combined with micro-lysimeter in 2015 and with weighing lysimeter in 2016. The results showed that the proposed surface resistance model improved the accuracy of the PM model, especially when the leaf area index was low and the greenhouse was being irrigated. We also found that the aerodynamic resistance calculated from the r_a^1 and r_a^3 methods is applicable to the greenhouse although the latter is slightly more accurate than the former. The proposed surface resistance model, together with the r_a^3 method for aerodynamic resistance, offers an improved approach to estimate ET in greenhouse using the PM formula.
