No-tillage enhances soil water storage, grain yield and water use efficiency in dryland wheat (Triticum aestivum) and maize (Zea mays) cropping systems: a global meta-analysis
Muhammad Adil
A , Siqi Lu B , Zijie Yao A , Cheng Zhang A , Heli Lu A C D E F G * , Safdar Bashir H , Mansoor Maitah I , Isma Gul J , Sehar Razzaq K and Lin Qiu L M
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Abstract
Climate change significantly affects crop production and is a threat to global food security. Conventional tillage (CT) is the primary tillage practice in rain-fed areas to conserve soil moisture. Despite previous research on the effect of tillage methods on different cropping systems, a comparison of tillage methods on soil water storage, crop yield and crop water use in wheat (Triticum aestivum) and maize (Zea mays) under different soil textures, precipitation and temperature patterns is needed. We reviewed 119 published articles and used meta-analysis to assess the effects of three conservation tillage practices (NT, no-tillage; RT, reduced tillage; ST, subsoil tillage), on precipitation storage efficiency (PSE), soil water storage at crop planting (SWSp), grain yield, evapotranspiration (ET) and water use efficiency (WUE) under varying precipitation and temperature patterns and soil textures in dryland wheat and maize, with CT as the control treatment. Conservation tillage methods increased PSE, SWSp, grain yield, ET and WUE in both winter wheat-fallow and spring maize cropping systems. More precipitation water was conserved in fine-textured soils than in medium-textured and coarse-textured soils, which improved ET. Conservation tillage increased soil water conservation and yield under high mean annual precipitation (MAP) and moderate mean annual temperature (MAT) conditions in winter wheat. However, soil water conservation and yield were greater under MAP <400 mm and moderate MAT. We conclude that conservation tillage could be promising for increasing precipitation storage, soil water conservation and crop yield in regions with medium to low MAPs and medium to high MATs.
Keywords: climate change, conservation tillage, conventional tillage, dryland cropping systems, fallow water conservation, food security, precipitation storage efficiency, water use efficiency.
Introduction
Climate change seriously endangers humans and biodiversity, and impairs agricultural productivity (Chandio et al. 2021). Climatic change-induced floods, changing patterns of rainfall and temperature, and loss of water reservoirs affect primary agricultural crop production (Appiah et al. 2018; Abbas 2022). In addition, improper field management practices, poor seed management, soil infertility, water scarcity and expensive field treatments play significant roles in decreasing crop productivity (Abdullaev et al. 2007). Global hunger and food insecurity are increasing due to increased population growth and stagnating agricultural production, compromising food security and access to sufficient, safe and nutritious food to fulfill dietary needs and food preferences (Boliko 2019). This has been further exacerbated by climate change (Boliko 2019).
Sustainable agriculture is essential for long-term land development; for example, these strategies are associated with low environmental hazards and better crop production (Busby et al. 2017). Regions such as the Middle East and Australia face soil problems because of land changes, deforestation and climatic conditions that have more detrimental effects on arid and semi-arid conditions (Nosrati and Collins 2019; Zeraatpisheh et al. 2020). Strategies are needed for developing land for the agriculture without depleting natural resources (Broman and Robèrt 2017).
Wheat (Triticum aestivum) is among the most important cereal crop species (Bruning et al. 2020; Adil et al. 2022a). It accounts for 40% of China’s food grains and is cultivated on 4.3 million ha of land on the Loess Plateau (Tong et al. 2003). It is planted on more than 0.89 million ha in the interior Pacific North-west of the United States (Schillinger and Papendick 2008). The wild grass in central Mexico were first cultivated to maize (Zea mays) approximately 7000 years ago (Ranum et al. 2014). As a crop that is grown worldwide, maize has an energy density of 365 kcal/100 g, and comprises approximately 72% starch, 10% protein and 4% fat. USA, China and Brazil are the top three maize-producing countries in the world, producing 563 of the 717 million metric tons of maize per year (Ranum et al. 2014).
Crop production in dryland areas is dependent mainly on precipitation. Conventional tillage (CT) leaves the soil bare after harvesting crops until the next crop is planted to retain precipitation water; farmers practise this approach in dryland regions of the USA, China and Canada (Adil et al. 2023). However, some studies have suggested that in dryland agricultural farming systems, CT using a moldboard plough is inefficient at conserving soil moisture during fallow periods (Cruse et al. 1982; Dao 1993). The soil becomes denser due to CT, forming a hardpan below the plough layer that impedes air and water flow, stunting root growth and eventually lowering crop production. Furthermore, wind erosion and soil deterioration are exacerbated by low precipitation (200 mm per year), and finely pulverised topsoil is generated by repetitive ploughing. It is generally believed that in a nutrient-deficient environment, water is the significant yield-limiting factor in dry areas (French and Schultz 1984). An even indication is that excessive rainfall may reduce crop yields in dryland agriculture systems (Mason and Fischer 1986), and inconsistent crop yields are obtained by different tillage systems (Su et al. 2007).
Conservation tillage is any method that aims to minimise soil and water loss (Benites et al. 1998). With this classification, many practices including shallow top and subsoil tillage (ST), reduced tillage (RT) and no-tillage (NT) are considered measures of conservation tillage (Rasmussen 1999; Lampurlanes et al. 2002). Conservation tillage systems were introduced as alternatives to conventional tillage systems (Schillinger 2001). Adopting conservation tillage is an important step in dryland farming to reduce the deterioration of soil physical and chemical properties and boost the water usage efficiency of crops (Huang et al. 2008). Since tillage impacts root growth in the subsoil, the development and dispersion of roots in the soil profile are crucial for a plant’s ability to absorb water and nutrients (Godwin 1990). However, tillage plays the most crucial role in a soil‒plant system, as continued use of the conventional tillage method creates a hard pan in soil that may negatively affect root proliferation below the plough layer (Maurya 1988; Gill and Aulakh 1990).
Several factors are considered in terms of how soil behaves when NTs are applied. These elements include soil characteristics, land management history, weather and the type and intensity of tillage applied (Mahboubi et al. 1993). Reduced tillage leads to a higher soil water content because it promotes soil penetration and decreases surface runoff and evaporation (Zhai et al. 1990). Moreover, conservation tillage can boost crop yield, lower operational costs and have positive economic effects (Gicheru et al. 2004; Fabrizzi et al. 2005). In contrast, Taa et al. (2004) reported that the yield of no-till wheat can occasionally be lower than that of conventionally grown wheat; for example, Lampurlanes et al. (2002) described that crop productivity and water use efficiency were not affected by the type of tillage system.
To our knowledge, no previous study has compared soil water conservation, crop yield or water use efficiency between winter wheat and spring maize crops under different tillage methods. Therefore, we aimed to determine how different tillage methods affect soil water storage, crop yield, and water use efficiency in these two important crops worldwide. We hypothesised that: (1) conservation tillage methods would have an overall positive effect on soil and plant parameters in both cropping systems compared to conventional tillage (CT); (2) such an effect would differ between winter wheat and spring maize and/or within conservation tillage methods; and (3) the edaphic and climatic conditions of several regions would modify the effects of different tillage methods on soil and plant parameters.
Materials and methods
Collection and screening of data
To evaluate the effect of fallowing methods on soil and plant parameters, we searched for peer-reviewed journals from 1973 to 2022 in Google Scholar and the Web of Science with the following keywords: soil water storage (SWS), precipitation storage efficiency (PSE), water use efficiency (WUE), evapotranspiration (ET), wheat and maize as affected by conventional tillage (CT), no-tillage (NT), reduced tillage (RT) and subsoil tillage (ST). A total of 845 publications were initially collected and screened by the following criteria:
Tillage methods should be tested in field cropping systems. In every study, conventional tillage (CT) was used as the control treatment. The NT, RT and ST should be compared with CT.
Experiments entirely dependent on natural precipitation should be selected, and irrigation should not be applied at any point throughout the experiment; for example, only precipitation should serve as the source of moisture.
Simulation and model studies were not included.
The data collection, partitioning, and selection process are in Fig. 1. Fig. 2 shows the geographic details of 119 trial sites around the globe. The literature compares several conservation tillage methods against conventional tillage during fallow.
Creation of the database
We homogenised the data into groups based on the various tillage methods. Mean annual air temperature (MAT) was grouped into three categories: (1) >15°C; (2) 8–15°C; and (3) 8°C. Mean annual precipitation (MAP) was grouped into three categories: (1) >600 mm; (2) 400–600 mm; and (3) 400 mm. There were three broad categories of soil texture: (1) fine; (2) medium; and (3) coarse. We manually estimated the PSE when the PSE was not calculated in previous publications but when the SWS with fallow precipitation was present (Nielsen and Vigil 2010). If the study did not contain information on latitude, longitude or weather, we collected these observations from an online search engine (https://www.whatsmygps.com). GetData Graph Digitizer software (ver. 2.20) was used to extract the data from the figures. The soil texture ranged from fine to coarse, the MAP ranged from 141 to 830 mm, and the MAT ranged from 4.1 to 22.1°C. We estimated the s.d. value with the formula:
where n is the number of samples.
In the studies where the soil water storage and fallowing precipitation were given but the PSE, WUE or ET were not determined, we manually estimated these variables with the formula (Nielsen and Vigil 2010; Zhang et al. 2015):
where ΔSWS is the difference in soil water storage at planting and harvest during the fallow period, and Pf is the precipitation during the fallow period.
The WUE was calculated as:
where ET is evapotranspiration, whereas ET was determined by the following soil water balance equation:
where ΔSWS is the change in soil water storage during the crop growing season, and Pg is the precipitation during the growing season.
We also collected data on climatic and geographical conditions, including longitude and latitude, fallow and annual precipitation, annual temperature, altitude, experimental location, duration of the experiment and publication year.
Data analysis
The effects of conservation tillage compared to those of CT were determined using the response ratio (RR) and the natural log of the RR taken as the effect size (Hedges et al. 1999):
where XCOT and XCT are the arithmetic mean fluxes of the soil and plant parameters (PSE, SWSp, yield, ET and WUE) under conservation tillage and CT, respectively. The comparison between CT and COT was performed separately for each experiment studied.
The error variance (V) within each experiment studied was calculated with the formula (Hedges et al. 1999):
where SCOT and SCT are the s.d. values for conservation tillage, and CT, NCOT and NCT indicate the number of replications for conservation tillage and CT, and XCOT and XCT are the mean values for conservation tillage and CT, respectively.
The reciprocal of the variance (V) taken as the weight (W) for each RR was determined with the formula (Lucas et al. 2011):
Studies with more variance are weighed less heavily during analysis than are those with less variance, a method given by (Hedges et al. 1999). The individual RR values of conventional and conservation tillage were used to calculate the overall mean response ratio (RRE++) as:
Within each category, ‘n’ represents the number of treatments, and ‘m’ is the number of comparisons. The standard error of RRE++ was calculated as:
The mean effect size of bias-based bootstrapping at the 95% confidence interval was calculated using the random model MetaWin 2.1 (Sinaure Associate, Inc., Sunderland, USA) to examine the effects of conservation tillage techniques on soil and crop parameters (SWSp, PSE, yield, ET and WUE). If the 95% confidence interval did not cross the zero line, the effect of the conservation tillage methods was considered significant. Using the Origin Pro 2023 program, the correlations of the RRs of wheat and maize yield, ET and WUE were compared to those of SWSp (OriginLab Corporation, USA).
Results
Tillage effects on winter wheat
There were 120 and 334 paired observations for PSE and SWSp, respectively (Fig. 3a, b). The data showed significant heterogeneities, with high Qt values of 112 for PSE and 321 for SWSp. Compared to CT, conservation tillage methods overall increased the PSE by 22.6% (P ≤ 0.05) (Fig. 3a). The most significant increase (25.1%) in PSE was obtained with RT, followed by that with ST (23.9%) and that with NT (15.9%) (P ≤ 0.05) across conservation tillage methods. The response ratio (RR) of the PSE to conservation tillage methods was significant for the overall soil texture (Fig. 4a). The medium- and coarse-textured soils increased the PSE by 22.1% and 16.4%, respectively, while the fine-textured soils increased the PSE by 25.7%. The enhancement effect of conservation tillage on the PSE was more significant when the MAP was >600 mm than when the MAP was 400–600 mm or <400 mm. In addition, conservation tillage increased the PSE in the regions where the MAT was 8–15°C compared with those where the MAT was >15°C or <8°C (Fig. 4a).
Mean response ratios of (a) precipitation storage efficiency (PSE), (b) soil water storage at wheat planting (SWSp), (c) winter wheat grain yield, (d) evaportranspiration (ET), and (e) water use efficiency (WUE) to conservation tillage methods during fallow period compared to conventional tillage (CT) and their bootstrapped 95% confidence intervals (horizontal line) as affect by soil texture in winter wheat. Conservation tillage methods are no tillage (NT), reduced tillage (RT), subsoil tillage (ST). The reference line (RR = 0) specifies no variation between conservation tillage and conventional tillage. Numbers accompanying the bootstrapped 95% confidence intervals designate the number of observations for comparisons.
Mean response ratios of (a) precipitation storage efficiency (PSE), (b) soil water storage at wheat planting (SWSp), (c) winter wheat grain yield, (d) evapotranspiration (ET), and (e) water use efficiency (WUE) to conservation tillage methods during fallow period compared to conventional tillage and their bootstrapped 95% confidence intervals (horizontal line) as affect by mean annual precipitation (MAP), and mean annual air temperature (MAT) in winter wheat yield. The reference line (RR = 0) specifies no variation between conservation tillage and conventional tillage. Numbers accompanying the bootstrapped 95% confidence intervals designate the number of observations for comparisons.
Compared with CT, conservation tillage methods increased the SWSp by 17.8% (P ≤ 0.05; Fig. 3b). This beneficial impact on the SWSp varied with tillage methods. Compared to CT, the SWSp in NT, RT and ST increased by 26.9%, 24.4% and 13.1%, respectively (P ≤ 0.05). Under all the soil textures, the RR of SWSp under the conservation tillage methods was significant compared to that under CT (Fig. 4b). In fine-textured soils, the SWSp increased by 26.4%, while the PSE increased by 22.1% and 17.7% in medium- and coarse-textured soils, respectively. The effects of conservation tillage on SWSp were significant under MAPs of 400–600 mm. The SWSp improved with conservation tillage methods in the regions where the MAT was less than 8°C (Fig. 4b).
A total of 331 observations were collected for grain yield, 34 for ET, and 103 for WUE. The data were heterogeneous for grain yield (Qt = 318), ET (Qt = 29) and WUE (Qt = 101) (Fig. 3c–e). Compared to those of CT, the overall conservation tillage methods enhanced the grain yield by 24.1% (P ≤ 0.05; Fig. 2c). According to the categorical meta-analysis, the grain yield increased by 31.4%, 21.1% and 18.2% with NT, RT and ST, respectively, compared to CT. The fine- and coarse-textured soils increased the grain yield by 20.3% and 22.1%, respectively, and the medium-textured soils increased the wheat yield by 24.1% (Fig. 3c). The enhancement effect of conservation tillage methods on grain yield was significant in the regions where the MAP was >600 mm. Conservation tillage methods also increased grain yield in the regions where the MAT was 8–15°C (Fig. 4c).
Overall, conservation tillage methods had a significant effect on wheat ET. NT and RT increased ET by 11.6% and 14.1%, respectively (P ≤ 0.05; Fig. 3d). However, ST had no significant effect on ET. Fine-textured soils increased ET by 18%, while medium- and coarse-textured soils enhanced ET by 2% each. The enhancement effect of conservation tillage methods on ET was significant under <400 mm MAP. Conservation tillage methods increased ET in the regions where MAT was >15°C (Fig. 4d).
WUE of winter wheat increased by 12.1% under the overall conservation tillage methods over the fallow period (P ≤ 0.05; Fig. 3e). Similarly, compared with CT, the NT, RT and ST increased the WUE by 18.4%, 11.3% and 5.4%, respectively. Overall, soil types exhibited an increase in wheat WUE when conservation tillage methods were applied. However, the medium-textured soils exhibited the most significant increase (22.3%) compared to the fine- and coarse-textured soils (Fig. 4e). Conservation tillage methods substantially positively impacted WUE in regions with MAP <400 mm. Moreover, conservation tillage methods increased the WUE in areas where the MAT was 8–15°C (Fig. 4e).
Tillage effects on maize
We gathered 76 paired observations for the PSE and 139 paired observations for the SWSp (Fig. 5a, b). As perceived by the high Qt values of 73 and 133 for the PSE and SWSp, respectively, the data showed strong heterogeneities. Compared to CT, conservation tillage methods generally enhanced the PSE by 38.1% (P ≤ 0.05) (Fig. 3a). The greatest increase in PSE was associated with NTs (45.7%), followed by STs (14.9%) (P ≤ 0.05). PSE increased by 28% in medium-textured soils and 17% in fine and coarse soils under conservation tillage methods compared to conventional tillage. Compared to CT, the RR of conservation tillage on the PSE was more significant in regions with a MAP <400 mm. Conservation tillage also increased the PSE in the regions where the MAT was 8–15°C (Fig. 6a).
Mean response ratios of (a) precipitation storage efficiency (PSE), (b) soil water storage at spring maize planting (SWSp), (c) spring maize grain yield, (d) evapotranspiration (ET), and (e) water use efficiency (WUE) to conservation tillage methods during fallow period compared to conventional tillage (CT) and their bootstrapped 95% confidence intervals (horizontal line) as affect by soil texture in spring maize. Conservation tillage methods are no tillage (NT), reduced tillage (RT), subsoil tillage (ST). The reference line (RR = 0) specifies no variation between conservation tillage and conventional tillage. Numbers accompanying the bootstrapped 95% confidence intervals designate the number of observations for comparisons.
Mean response ratios of (a) precipitation storage efficiency (PSE), (b) soil water storage at spring maize planting (SWSp), (c) spring maize grain yield, (d) evapotranspiration (ET), and (e) water use efficiency (WUE) to conservation tillage methods during fallow period compared to conventional tillage and their bootstrapped 95% confidence intervals (horizontal line) as affect by mean annual precipitation (MAP), and mean annual air temperature (MAT) in spring maize cropping system. The reference line (RR = 0) specifies no variation between conservation tillage and conventional tillage. Numbers accompanying the bootstrapped 95% confidence intervals designate the number of observations for comparisons.
Overall, SWSp was enhanced by 20.6% under conservation tillage methods, compared to CT (P ≤ 0.05; Fig. 5b). However, the beneficial impact on the SWSp differed according to the tillage methods. Compared to that under CT, the SWSp under NT increased by 36.1%, that under RT increased by 3.8%, and that under ST increased by 4.9% (P ≤ 0.05). For all the soil textures, the RRs of SWSp under the conservation tillage methods were more favourable than those under the CT method (Fig. 6b). In addition, the SWSp increased by 26.4% in the fine-textured soils, while the PSE increased by 22.2% and 17.1% in the medium- and coarse-textured soils, respectively. When the MAP was 400–600 mm, the RR resulting from conservation tillage on SWSp was greater than that on CT. Additionally, conservation tillage increased the SWSp in areas where the MAT was between 8 and 15°C.
In total, 158 observations were measured for grain yield, 97 for ET and 58 for WUE. The data were heterogeneous for yield (Qt = 154), ET (Qt = 89) and WUE (Qt = 52) (Fig. 5c–e). Compared with CT, conservation tillage methods increased grain yield by 29.6% (P ≤ 0.05; Fig. 5c). The categorical meta-analysis showed that NT, RT and ST increased grain yield by 33.1%, 23.8 and 21.2%, respectively. The RR of yield under conservation tillage methods was positive for all soil textures (Fig. 6c). Coarse-textured soils increased yields by 25.5%, while fine- and medium-textured soils increased grain yields by 11.1% and 16.2%, respectively. Compared to that of CT, the RR of conservation tillage on grain yield was greater when the MAP was <400 mm. Conservation tillage increased the grain yield when the MAT was >15°C (Fig. 6c).
Overall, conservation tillage methods had a significant effect on crop ET. Compared to CT, the NT, RT and ST increased spring maize ET by 10.1%, 14.7% and 16.8%, respectively (P ≤ 0.05; Fig. 5d). In addition, medium-textured soils increased ET by 18%, while 12.0% and 9.7% increments were observed under fine- and coarse-textured soils, respectively. Compared to that of CT, the RR of conservation tillage on ET was greater when the MAP was <400 mm. Conservation tillage also increased ET in the regions where MAT was <8°C compared with those where MAT was >15°C and 8–15°C (Fig. 6c).
WUE of maize increased by 11.0% with overall conservation tillage practices (P ≤ 0.05; Fig. 5e). NT, RT and ST increased WUE by 19.4%, 3.1% and 10.7%, respectively. Maize WUE increased with conservation tillage during the fallow period in all the soils. However, the effect of conservation tillage methods was more prominent in medium-textured soils, in which the WUE increased by 21.3% (Fig. 6e). Compared to that of CT, the RR of WUE under conservation tillage was greater when the MAP was <400 mm. The conservation tillage methods also increased the WUE when the MAT was >15°C (Fig. 6c).
Discussion
Effects of conservation tillage methods on winter wheat
Averaged across all the locations, conservation tillage methods overall increased the winter wheat PSE, SWSp, grain yield, ET and WUE by 22.6%, 17.8%, 24.1%, 6.5% and 12.1%, respectively (P ≤ 0.05; Fig. 3), which corresponds to the findings of a recent meta-analysis by Adil et al. 2022b) that described the positive effects of conservation tillage methods and fallow mulching in dryland cropping systems and to the results obtained by Li et al. (2007) where it was found that conservation tillage methods are effective at increasing soil water storage and crop yield. The positive effect of conservation tillage methods on soil water storage compared to that of conventional tillage confirmed our first hypothesis that conservation tillage methods improve soil water storage during the fallow period, which is probably due to reduced soil disturbance, reduced soil bulk density and improved aggregate stability caused by NT (Joseph Oyedele et al. 1999; Zhang et al. 2007). Similarly, conservation tillage methods are effective at reducing soil compaction and improving soil structure, eventually increasing yield and WUE (Pikul and Aase 1999, 2003). Moreover, previous studies in the Chinese Loess Plateau also reported higher water content and yield with conservation tillage methods during the fallow period than with CT (Liang et al. 2002; Wang et al. 2003), which is consistent with the results of the current meta-analysis that also corresponds to previous studies conducted in other areas, including Victoria (Australia), Nebraska (USA) (Lyon et al. 1998; Cantero-Martinez et al. 1999), Texas (USA) (Baumhardt and Jones 2002), the Great Plains of the northern USA (Lenssen et al. 2007) and semi-arid Kenya (Gicheru et al. 2004).
Compared with CT, we found that RT increased the PSE in winter wheat by 25.1%; this effect was slightly greater than that of ST (23.9% increase compared with CT) (Fig. 3). ST had better results than CT may be due to the deep loosening of the soil, which results in better infiltration and breaching of the permanent flow paths in the soil (Hillel 1998). However, compared with CT, NT increased the PSE by 10.9% (Fig. 3), as Halvorson et al. (2000) described the effects of NT and CT under dry conditions. Our study observed a 24.1% increase in wheat yield with NT compared to that with CT. Similar results were obtained by Jin et al. (2007), who reported that after 6 years of experimentation, NT had the highest yield by improving soil physical and chemical properties and stabilising the bulk density of soil after 5 years of NT practice (Fabrizzi et al. 2005).
Effects of conservation tillage methods on spring maize
Compared with CT, conservation tillage methods also increased the PSE, SWSp, grain yield, ET and WUE in the spring maize cropping system by 38.1%, 20.6%, 29.6%, 16.9% and 11.0%, respectively (P ≤ 0.05; Fig. 5), which corresponds to the results obtained by Li et al. (2007) and He et al. (2009) where it was demonstrated that conservation tillage methods effectively improved soil water storage and crop yield. Among conservation tillage methods, the highest PSE (45.7%) and SWSp (36.1%) were observed with NT (Fig. 3), which confirms our second hypothesis (such as the highest PSE under the wheat cropping system was obtained by RT; Fig. 3) that the effects of conservation tillage methods will differ among winter wheat and spring maize cropping systems. This is in agreement with Jin et al. (2007) where it was found that NT is the best tillage practice in a fallow period for water conservation with effective precipitation storage efficiency (Fig. 5). Similarly, the greatest increases in maize yield (33.1%) and WUE (19.4%) were obtained with NT, which corresponds to the results of Li et al. (2007) and He et al. (2009) where it was shown that conservation tillage methods are effective methods and can reduce soil compaction and improve soil structure, which eventually increases yield and WUE (Pikul and Aase 1999, 2003). Previous studies on the Loess Plateau by Liang et al. (2002) and Wang et al. (2003) also reported higher water content and grain yield with conservation tillage methods during the fallow period than with CT, which was consistent with the findings in other areas, including Victoria (Australia), Nebraska (USA) (Lyon et al. 1998; Cantero-Martinez et al. 1999), Texas (USA) (Baumhardt and Jones 2002), the Great Plains of the northern USA (Lenssen et al. 2007) and semi-arid Kenya (Gicheru et al. 2004).
Variations with soil textures and climatic conditions
The soil and climatic conditions of several regions affected soil water storage with conservation tillage methods more than with conventional tillage methods, as coarse-textured soils stored the lowest amount of water compared to fine-textured soils. In contrast, the RRs of fine- and coarse-textured soils were quite similar under the overall conservation tillage methods (Figs 3 and 4), which is consistent with the findings of McConkey et al. (1996) who reported that the lowest soil water volume was observed in sandy loam in 1983 and in silty loam and clay soil in 1990. Similarly, for silt loam, the SWSp estimated with CT and NT were 123 and 125 mm and 31, 128 and 128 mm for RT and NT, respectively. Increased SWSp in fine soils and PSE, crop yield and WUE in medium-textured soils (Figs 3 and 5) indicate that coarse- to medium-textured soils store more water and improved yields in both crops. An increase in initial soil moisture storage was reported in clay soil with NT, and as a result, a greater crop yield was expected (Cox et al. 1986; Tanaka and Aase 1987), while lower yields were obtained with NT under silt loam (Tessier et al. 1990).
According to Hammel et al. (1981), soil texture affects soil hydraulic properties, which may impact how much water is lost when using different tillage methods. For example, Papendick et al. (1973) reported that the average WUE of conservation tillage methods over 3 years of study was significantly greater than that of CT. Large fluctuations in diurnal temperature occur in the top 15 cm of soil. These factors may affect vapour movement in the northwestern dry layer, where most water loss occurs in fallow land within a dry layer 10 cm or greater in thickness (Papendick et al. 1973). Macro pores and cracks can also affect the water balance with RT in the bare fallow period (Hartzog and Adams 1989) because of the rapid downward water movement, which significantly contributes to the fallowing performance in terms of cracking the clay soil texture in southern Queensland (Marley and Littler 1989). Deep water movement in the NT fallows explained the cracking behaviour of the soil at Dooen (Australia). At the same time, the saturated hydraulic conductivity significantly increased at nearby locations from 14 mm to more than 200 mm h−1 after 10 years of NT (Bissett and Oleary 1996), while NT accumulated 47 mm more water than CT (O’Leary and Connor 1997).
Conservation tillage methods significantly affected the winter wheat PSE, SWSp, crop yield, ET and WUE under all the precipitation patterns except for the WUE with >600 mm MAP, which remained not significant (Fig. 4). Similarly, a MAP >600 mm had a non-significant effect on the spring maize PSE, except that the conservation tillage had a significant effect on all the variables (Fig. 6). Similarly, more significant positive RRs for crop yield and WUE were achieved with conservation tillage practices when the MAP was <400 mm, which corresponds to the findings of Jin et al. (2007), who reported that NT was the best tillage practice during the fallow period for water conservation, during which the effective storage efficiency of rainwater led to higher winter wheat yield and PSE. Similarly, the spring maize yield with >600 mm MAP was relatively low compared to that with <400 mm MAP (Fig. 6), which could be due to the saturated field conditions at the end of the fallow period and the delay of sowing the main crop (Jin et al. 2007). Similarly, the difference between conservation and conventional tillage was more pronounced with relatively dry rainfall (365 mm and 292 mm) years, as overall, 42% of fallow precipitation was stored in the soil with comparatively low runoff, which means that 58% of fallow precipitation vanished due to evaporation (Jin et al. 2007). However, the advantages of conservation tillage for soil differ depending on the amount of rainfall and type of soil texture (Gajri et al. 2002). Previous studies have shown that the degree and depth of soil disturbance under the NT, ST and CT treatments affect rainfall infiltration, soil water holding capacity and ET (Huang et al. 2006). In 3 years of research, regardless of rainfall during the fallow season, the water storage status improved to varying degrees with all the tillage methods. Compared to those in the CT treatment, the SWS and PSE in the NT and ST treatments increased to more effectively store fallow precipitation in the soil (Hou et al. 2012). Conservation tillage methods with less soil disturbance enhance rainfall penetration and decrease soil water evaporation (Pikul and Aase 2003; Li et al. 2007). By removing the plough pan layer, ST considerably reduces the soil bulk density and allows more precipitation to be stored in the soil (Pikul and Aase 1999; Mohanty et al. 2007). In contrast, excessive soil tillage (CT) leads to a relatively high rate of soil water evaporation (Debaeke and Aboudrare 2004).
Correlations of wheat and maize grain yield, ET and WUE with SWSp
The RRs of wheat and maize grain yield increased linearly with the RR of SWSp for conservation tillage practices (Fig. 7). An increase of 24.1% in wheat yield and 29.6% in maize yield can be explained by the increase in the RR of SWSp for conservation tillage practices. The RR of ET to SWSp under conservation tillage methods was significant for wheat but remained not significant for maize. Similarly, the RRs of wheat and maize WUE were also related to that of SWSp, which can be attributed to a 12.1% increase in wheat WUE and an 11.0% increase in maize WUE under conservation tillage methods (Fig. 7).
Conclusion
Our meta-analysis showed that compared to conventional tillage, overall conservation tillage methods increased soil water storage, grain yield and crop water use in winter wheat and spring maize cropping systems. However, the effectiveness was more significant for spring maize than for winter wheat. Soil texture and precipitation patterns played a significant role in determining the results. In both cropping systems, fine-textured soil increased soil water storage and ET, while medium-textured soil increased grain yield and water use. High precipitation increased soil water storage, which increased grain yield. We conclude that conservation tillage could be a promising practice for increasing precipitation storage, soil water conservation, and crop yield in regions with medium to low MAP and medium to high MAT. However, among conservation tillage methods, NT is a promising global practice that can be applied to increase soil water storage and crop production in dryland wheat and maize cropping systems.
Conflicts of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Declaration of funding
This study is under the auspices of the Scientific and Technological Research Projects in Henan Province (242102321158, 232102320047) and Xinyang Academy of Ecological Research Open Foundation (2023XYMS02).
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