Groundwater Dynamics under Water Saving Irrigation and Implications for Sustainable Water Management in an Oasis: Tarim River Basin of Western China

Abstract. Water is essential for life. Specifically in the oases of inland arid basins, water is a critically limited resource, essential for the development of the socio-economy and the sustainability of eco-environmental systems. Due to the unique hydrological regime present in arid oases, a moderate groundwater table is the goal of sustainable water management. A shallow water table induces serious secondary salinization and collapse of agriculture, while a deep water table causes deterioration of natural vegetation. From the hydrological perspective, the exchange flux between the unsaturated vadose zone and groundwater reservoir is a critical link to understanding regional water table dynamics. This flux is substantially influenced by anthropogenic activities. In the Tarim River basin of western China, where agriculture consumes over 90% of available water resources, the exchange flux between the unsaturated vadose zone and groundwater reservoir is influenced strongly by irrigation. Recently, mulched drip irrigation, a sophisticated water-saving irrigation method, was widely applied in the Tarim River basin, which greatly impacted the exchange flux and thus the regional groundwater dynamics. Capitalizing on recent progress in evaporation measurement techniques, we can now close the water balance and directly quantify the exchange flux at the field scale, thus gaining a better understanding of regional groundwater dynamics. In this study, comprehensive observations of water balance components in an irrigated cropland were implemented in 2012 and 2013 in a typical oasis within the Tarim River basin. The water balance analysis showed that the exchange flux and groundwater dynamics were significantly altered by the application of water-saving irrigation. The exchange flux at the groundwater table is mostly downward (310.5 mm year−1), especially during drip irrigation period and spring flush period, while the upward flux is trivial (16.1 mm year−1) due to the moderate groundwater table depth (annual average depth 2.9 m). Traditional secondary salinization caused by intense phreatic evaporation (fed by upward exchange flux) is alleviated. However, a new form of secondary salinization may be introduced unwittingly if there is lack of water for periodic flushing, especially when brackish water is used in the irrigation. Furthermore, the water saved via drip irrigation has been used in further growth of irrigated lands instead of supporting the ecological system. This could lead to an increased risk of eco-environmental degradation and calls for improved governance schemes. The insights gained from this study can be potentially applied to other arid inland areas (e.g., central Asia) which face similar water shortages and human development problems.

Core Ideas Estimation of water table level supplies upward water flux for daily ETc needs. Episodic master recession method informs water table control during rain events. Water table recession varies by soil and irrigation, with fastest rates under subirrigation. Irrigation depth may be reduced in sprinkler areas with water table management. Agricultural areas with shallow water tables usually rely on upward soil water flux to supply crop evapotranspiration (ETc). The study objective was to determine optimum water table levels for coarse‐textured soils cultivated with potato ( Solanum tuberosum L.) by estimating the upward soil water flux under different irrigation methods. Potato was grown under seepage, subirrigation with tile drainage, subsurface drip irrigation (SDI), and sprinkler irrigation. Irrigation zones were classified as sandy soil with low soil organic matter (SOM) and high bulk density ( B d ), or loamy sand soil with high SOM and low B d . Upward soil water flux supplied enough water to the root zone to meet ETc when the water table was at the 69‐cm depth for loamy sand soils under seepage, and 42 and 45 cm for sandy soils under subirrigation and SDI, respectively. The sprinkler‐irrigated area had no control over the water table, whereby the cumulative contribution of upward water flux still averaged 6.3 cm, suggesting that irrigation rates could be reduced if the water table is controlled and upward flux accounted for in the crop water balance. Rainfall introduces flooding risks and crop losses, but these risks are minimized with management. The water table elevation/precipitation ratio was 34.4 and 25.6 cm cm −1 of rain for loamy sand and sandy soils. After precipitation, the water table returned to the original levels twice as fast under subirrigation than with other methods given improved drainage capacity. Soil characteristics, irrigation method, upward water flux, and proper water table management are important factors for maintaining ideal soil moisture conditions in the crop root zone, minimizing flooding risk.

Effect of irrigation methods on root growth, root-shoot ratio and yield components of cotton by regulating the growth redundancy of root and shoot

The mulched drip-irrigation technique has been widely employed in Xinjiang, China, however, it was found to result in the buildup of salt in the surface soil. To ascertain the effect of mulched drip irrigation on salinization, experiments were carried out during 2009–2010 in two fields of mulched soil drip irrigated for three and 13 years. The solute transportation in soil was simulated with the MATLAB system based on the Richards equations. Results showed that the soil mulched by plastic film did not accumulate salt, but the bare soil surface accumulated salt and the salinity distribution in bare soil was in the ‘Γ’ pattern. The soil layer below a depth of 20 cm in the bare area showed desalination because its salt content was 22% less than the surface. The salinity of bare surface soil including cultivated horizon was reduced by 17% after 13 years of drip irrigation. The simulation results indicated that the solutes of mulched soil were transported vertically to deep soil and transversely to the bare soil with drip irrigation. Thus, the salt accumulated on the surface of bare soil came from the soil mulched by plastic film, not from groundwater or saline irrigation water and did not cause secondary salinization.

Mulch drip irrigation (MDI) technology can effectively solve the problem of insufficient temperature accumulation during the pre-fertility period and facilitate the efficient supplementation of water and fertilizer during the fertility period in spring corn planting. Moreover, this local MDI technology also has impacts on the farmland environment. To investigate the effect of drip irrigation technology on the water and salt environment of farmland, a field study on corn cultivation was carried out at West Liaohe Plain. In addition, the water and salt dynamics of the farmland were simulated using HYDRUS-2D for mulch drip irrigation (MDI), shallowly buried drip irrigation (SBDI), and sprinkler irrigation (SI), with variable rainfall and initial salt content. The results showed that the distribution of and variation in water and salt in the soil were similar under MDI and SBDI. The change near the drip tape was mainly affected by irrigation, while the water and salt in the soil between drip tapes were correlated with irrigation and rainfall. The amount of salt in the topsoil (5 cm) increased with a decrease in rainfall. With an initial EC = 480 μs/cm (soil salt content 0.1%), the salinity of the topsoil under MDI was significantly higher than that under SBDI and SI within two years. The topsoil salinity was similar for all three irrigation technologies with increasing operating life, reaching a relatively stable state, and much lower than the salinity determination threshold of 480 μs/cm. Given the current conditions of rainfall, soil, buried depth, and mineralization in the West Liaohe Plain, the risk of secondary salinization is minimal if irrigation management is reasonable. This study provides data to support the application of drip irrigation technology in the Western Liaohe Plain.

Mulched drip irrigation increases cotton yield and water use efficiency via improving fine root plasticity

Assessing the impacts of irrigated agriculture on hydrological regimes in an oasis-desert system

Pigment with high heat stability

Evaporation of maize crop under mulch film and soil covered drip irrigation: field assessment and modelling on West Liaohe Plain, China

It is of great significance to optimize water resource management and promote sustainable development in the Tarim River Basin (TRB) by using the water footprint (WF) evaluation method to evaluate the water shortage of fruit trees in the TRB and analyse its water-saving potential. This study aimed to elucidate the WF spatial–temporal distribution characteristics of fruit trees in the water-limited TRB from 2000 to 2020 and evaluate their water-saving potential capability. The WF was calculated using a combination of irrigation technology simulation and water usage assessments for four different fruit trees (apple, pear, date, and walnut). The results indicate that the green WF (WFgreen) initially increased and then decreased, reaching its lowest value of only 175.09 m3/t in 2020, and decreased by 22.71% from 2000 to 2020. WFblue decreased by 47.13% over the same period. In 2020, the WFblue of date and walnut accounted for a higher percentage of WFblue. WFblue significantly exceeded WFgreen, indicating their high water consumption and the limited adoption of water-saving technologies in the study area. Due to the increase in fruit tree planting area and fertilization, WFgrey exhibited an overall upward trend. Meanwhile, the total WF (WFtotal) indicated a general downward trend, though the walnut tree had the highest WFtotal at 2.21 × 105 m3/t, indicating the popularization of water-saving technology. The results show that, taking 2020 as the baseline, the WFblue of the four fruit trees in the TRB was 2.64 × 105 m3/t (accounting for 89.1%), total WFblue decreased by 0.73 × 105 m3/t (a decrease of 48.38%) after drip irrigation, and the water-saving potential in the five prefectures of the TRB was in the range of 38.55–56.18%. Therefore, the promotion of drip irrigation technology plays a key role in alleviating the water pressure of fruit trees and promoting the sustainable utilization of water resources in the TRB.

Assessment of maize yield-increasing potential and optimum N level under mulched drip irrigation in the Northeast of China

Characteristics of carbon emissions in cotton fields under mulched drip irrigation

Compared to either drip irrigation or mulching with plastic film, the two methods together can reduce water requirements of crops grown in arid areas by more than 30%. Such a combination deployed on a large scale (1) reduced the loss of soil water by 31.8% compared to that from drip irrigation alone; (2) narrowed the range of annual evapotranspiration from 1582.4-1780.3 mm, which is average for the basin, to 222.2-294.8 mm; and (3) increased the overall humidity in the central plain of the basin. However, the surrounding regions in which drip irrigation is not combined with mulching are getting more arid; thus, as a result of the water-saving technology, both oases and the desertification of the river basin are increasing at the same time. The results of the study further the understanding of the effects of drip irrigation combined with mulching on water cycles in the basin of the Manas river and suggest ways to protect the ecology and the environment of the basin. Keywords: evapotranspiration, drip irrigation, arid inland areas, water cycle, Mann-Kendall rank test, MOD16, Manas river basin DOI: 10.25165/j.ijabe.20191201.4031 Citation: Li P F, Yang G, He X L, Li F D, Yan K , Wang Z L. Effects of drip irrigation on components of water cycle in arid inland areas: A case study of Manas river basin in northwestern China. Int J Agric & Biol Eng, 2019; 12(1): 132–138.

To explore the effects of different irrigation approaches, mulching, and their interaction on greenhouse melon (Cucumis melo L.) production and water use, a field experiment was conducted in Northern China using four treatments: mulching drip irrigation (MDI), mulching furrow irrigation (MFI), drip irrigation (DI), and furrow irrigation (FI; CK). The plant biomass, yield, water consumption, and water use efficiency (WUE) of melons were measured at different growth stages. The results showed that mulching has significant positive impacts on the growth as well as the fruit yield of melons. However, the water use characteristics of the plant were more greatly determined by the various irrigation approaches, and there was a significant interaction between the irrigation approach and mulching for both the total water consumption and WUE of the greenhouse melon. Of these treatments, MDI resulted in the highest yield of 38.49 t/hm2, which was significantly higher than the yields obtained with DI (32.36 t·hm−2) and FI (CK, 30.34 t·hm−2). In addition, the water consumption under MDI was 45.80% lower than FI (CK), which resulted in the promotion of WUE under MDI. The WUE range of the greenhouse melon is as follows: MDI (334.77 kg·mm−1·hm−2) > DI (244.84 kg·mm−1·hm−2) > MFI (189.78 kg·mm−1·hm−2) > FI (CK; 142.94 kg·mm−1·hm−2). The findings of this study indicate that mulching can boost melon yield, and drip irrigation can limit water consumption. This study provides a reference point for policymakers, indicating that drip irrigation with plastic mulching could be a feasible adaptation strategy for increasing greenhouse melon production in Northern China, as well as other agriculture regions that suffer from water shortages.

Context Leaves at different heights in a canopy have differential roles on photosynthetic characteristics and yield but have not been compared systematically under plastic film mulching with drip irrigation. Aims To determine the temporal and spatial variation of morpho-physiological characteristics in relation to the benefit of mulched drip irrigation in spring maize growth. Methods Field experiments were conducted in northeastern China during 2017 and 2018 that included mulched drip irrigation (MD), non-mulched drip irrigation (ND), and traditional non-mulched rain-fed (CK) treatments. Key results MD significantly increased lower leaf area by 13.1–62.3%, upper leaf N content (Nmass) by 6.3–13.0%, and upper leaf photosynthetic capacity (Amax) and maximum carboxylation rate (Vcmax) by 13.4–42.3% and by 4.7–11.6%, respectively. There were close correlations between leaf physiological parameters (Nmass, carbon isotope discrimination (Δ), Amax, and Vcmax), and also between morphological parameters (leaf area (LA) with leaf mass per area (LMA), and LMA with leaf dry matter content (LDMC). As for time scale, leaf morphological parameters (LA, LMA, and LDMC) in the reproductive stage (R-stage) were higher than those in the vegetative stage (V-stage), while physiological parameters (Nmass, Amax, and Vcmax) were higher in the V-stage. This study indicated that MD treatment increased the photosynthetic area of lower leaves and the photosynthetic capacity of upper and middle leaves compared with non-mulched rainfed CK. In addition, an increase of net radiation absorbed by the canopy in MD was likely to correspond to a higher net photosynthetic rate, which was beneficial to yield accumulation in the treatment. Conclusions This study provided relevant information for the simulation of water and carbon flux under mulched drip irrigation. Implications The research explained that the morpho-physiological characteristics of leaves at different canopy heights played different role on affecting maize yields under plastic film mulched drip irrigation.