Enhancement growth, water use efficiency and economic benefit for maize by drip irrigation in Northwest China

The application of drip irrigation has been paid more and more attention, but there was lack of systematic comparative analysis between drip irrigation and conventional border irrigation method for maize, currently. A 7-year field study from 2015 to 2021 evaluated the effects of drip irrigation (DI, 540 mm) or conventional border irrigation method (BI, 720 mm) on maize growth, water use efficiency (WUE) as well as profitability. The results showed the plant height, leaf area index, yield, WUE and economic benefit of maize with DI had significantly higher than BI. The dry matter translocation, the dry matter transfer efficiency and contribution of dry matter translocation to grain with DI showed significant increase of 27.44%, 13.97% and 7.85% compared to BI, respectively. In comparison to conventional border irrigation, the yield of drip irrigation increased by 14.39%, as well as WUE and irrigation water use efficiency (IWUE) increased by 53.77% and 57.89%. The net return and economic benefit of drip irrigation was 1998.87 and 756.58 USD$ hm−1 higher than that of BI. Drip irrigation increased net return and benefit/cost ratio by 60.90% and 22.88% compared with BI. These results demonstrate that the drip irrigation can effectively improve the growth, yield, WUE and economic benefit of maize in northwest China. Therefore, drip irrigation can be used for maize cultivation to increase crop yield and WUE in northwest China, which has cut down on irrigation water about 180 mm.

The distribution of water resources in China is uneven, which is manifested in the rich southeast and the lack of northwest. The shortage of water resources has become an important factor restricting the development of agriculture in northern China 1 . At present, China's agricultural water consumption accounts for more than 70% of total water consumption, and irrigation water accounts for 90-95% of agricultural water consumption 2 . For the northwest region with relatively less water resources, cotton, wheat and maize are the main crops. The crops growth is closely related to water availability 3 . How to make economic and effective use of water resources and implement reasonable irrigation measures are the core issues of agricultural production 4,5 . Therefore, it is imperative to optimize irrigation method to improve WUE.
Due to difference of various irrigation technologies, a significant part of agricultural research is focused on improving WUE and conserving water without yield penalties 6 . Conventional border irrigation has high irrigation quota, poor uniformity, difficult to control, and large field evaporation, which makes it difficult to further improve yield and WUE 7 . Drip irrigation technology is a new type of surface irrigation technology for the development of water-saving agriculture 8 , which has proven to be successful in saving water and improving yields. Suryavanshi et al. 9 found that drip irrigation increased wheat yields compared to sprinkler and pool irrigation. Zhang et al. 10 and Liu et al. 11 found that compared with furrow irrigation, drip irrigation at-30 kPa enhanced yield by 4.3-15%, increased net profit by 3.1-23%, and reduced water application by 57%. Raina et al. 12 found that drip irrigation besides giving a saving of 54% irrigation water resulted in 40% higher fruit yield compared with www.nature.com/scientificreports/ the surface irrigation. Due to the different irrigation amount and irrigation intensity of different water-saving irrigation techniques 13 , irrigation method directly affects the growth and development of maize 14 . Qin et al. 15 research results show that under different irrigation methods, drip irrigation not only achieve the role of water saving, but also on the growth of maize can play a role in increasing production. O'Neill et al. 16 showed that by using furrow irrigation to produce the same number of maize grains, subsurface drip irrigation saves nearly 30% of the total water consumption (irrigation, rainwater, soil water), while sprinkler irrigation saves nearly 8% of the water consumption. Mehriya et al. 17 reported that maximum water-use efficiency 5.7 kg hm −1 and water saving 39.04% was observed under drip irrigation. Until now, Irrigation research not only focuses on promoting maize growth, but also on yield, water distribution, water use efficiency, and so on. There are few long-term comparative studies on drip irrigation and conventional border irrigation in Northwest China. The lack of long-term research cannot systematically explain how much benefit has been brought to maize production in northwest China since water-saving irrigation. We assume that drip irrigation has the advantages of promoting maize growth, improving WUE and economic benefits, compared with conventional border irrigation. Much of these previous works were quantitative assessments conducted of short-term effects (≤ 2 years) and were limited to a specific aspect (soil conditions or crop characteristics). For Xinjiang, China, there are no published results of long-term drip irrigation versus conventional border irrigation for maize. In this paper, aiming at the same research area, the effects of drip irrigation and conventional border irrigation on maize growth, IWUE and economic benefit were studied by 7 years of comparative experiments under the same soil texture and planting mode. Therefore, this analysis provides a scientific basis for the promotion and application of water-saving irrigation methods for maize planting and a theoretical basis for the sustainable development of agriculture in arid areas.

Material and methods
Experiment site. Field experiments were conducted in the Crop Water Use Experiment Station of the Ministry of Agriculture in Shihezi City, northern China (86° 09′ E, 45° 38′ N) from 2015 to 2021. The region has a temperate continental climate, with an annual average sunshine time of about 2770 h. The accumulated temperature above 10 °C is 3649 °C. The average annual rainfall is 125.0-207.7 mm, and the average annual evaporation is 1942 mm. The maximum/minimum temperatures and mean precipitation for the growth season in 7 years during the maize growth periods are shown in Fig. 1. The groundwater depth varies from 2 to 3 m in different years. The soil type is gray desert soil. Seven-year averages of the soil's physicochemical properties are shown in Table 1.

Experimental design.
A field experimental design consisting of three replicates were used in the study, with drip irrigation (DI) and conventional border irrigation (BI). The irrigation quota of drip irrigation was 540 mm, while the irrigation quota of conventional border irrigation was 720 mm, which refer to the local farmer irrigation quantity. Drip irrigation uses an integrated water and fertilizer irrigation model. The conventional border irrigation, the seedling water is sown with seed fertilizer, and the later irrigation adopts the simple water and fertilizer integration mode. The irrigation and fertilization levels in each growth period and the whole growth period is shown in Table 2. Drip irrigation maize sowing, harvesting, and sampling time are shown in Table 3. Considering the marginal effect of different irrigation methods, the 6 plots were separated from adjacent plots by 2.2 m-wide isolation strips, and the size of each plot (110 m 2 ) was 20 m long and 5.5 m wide. In each plot, water reading meter and fertilizer tank were installed to monitor the amount of irrigation water and fertilizer that were applied, respectively.   The source of irrigation water was a deep well with a depth of 100 m; the salinity of the water was 0.2-0.3 g L −1 . The type of drip irrigation belt was a single wing labyrinth drip-irrigation belt (WDF16/2.6-100) produced by Xinjiang Tianye Company (Shihezi, China). The wall thickness was 0.18 mm, the inner diameter was 16 mm, the drip hole spacing was 300 mm, the rated flow was 2.0 L h −1 , and the working pressure was 0.1-0.15 MPa.

Sampling and measurements
Stand growth index. Plant height. Ten maize plants with the similar growth were randomly selected from each treatment at flowering and maturity stages, and the height from the ground to the top of the maize plants was measured by tape 18 .
Leaf area index (LAI). Ten representative plants were selected from the central rows of each plot to determine the green leaf area (GLA) non-destructively at flowering and maturity stages. Leaf length (L) and maximum width (W) were recorded and used to calculate GLA.
where N is the number of plants within a unit area of land and S is the unit area of land 19 .

Soil and plant analyzer development (SPAD).
The SPAD-502 chlorophyll meter (Minolta, JPN) was used to determine the ear leaves of ten maize plants randomly and continuously selected at flowering and maturity stages.
Dry matter determination. At flowering and maturity of maize, four maize plants of uniform growth were randomly selected from each treatment, cut from the bottom of the stems of the plants with scissors, and the leaves, stems, and reproductive organs 20 at a later stage were put into archival bags and weighed in fresh weight, after which the weight of dry matter was measured using the drying and weighing method. All the plant samples were heated for 30 min at 105 °C and then dried at 85 °C to a constant weight. Each plant fraction was weighed to obtain its dry-matter weight.
Yield and its components. During the maize maturity period, random sampling was done for each plot.
Twenty maize plants were chosen continuously at each point, and the length of the panicles, the number of rows, and the length of the baldness was measured, and then the ears of the maize were threshed. The grain was airdried and weighed (called its 1000-grain mass and total grain mass), then converted into yield per hectare. Grain yield and kernel weight were expressed at 14% moisture content.
Dry matter translocation (kg hm −2 ) = stem and leaf dry matter at flowering stage − stem and leaf dry matter at maturity stage; Dry matter transfer efficiency (%) = dry matter translocation/stem and leaf dry matter at flowering stage ×100; Contribution of dry matter translocation to grain (%) = dry matter translocation/grain yield × 100 22 . www.nature.com/scientificreports/ Water use efficiency (WUE) 23 . Seasonal evaporate-transpiration (ET) was estimated using water balance approach where P, precipitation; I, irrigation; C p , contribution through capillary rise from groundwater; D p , deep percolation; R f , runoff; ΔS = S f − S i , change in the soil water storage in the profile; where S i , soil water storage in the profile at sowing and S f , soil water storage in the profile at harvest. Due to the depth of groundwater between 2 and 3 m, C p was assumed negligible. D p was considered negligible beyond 90 cm because of negligible changes in the soil moisture storage below 90 cm soil depth. There was no run off (R f ) from the field as all the plots were provided with bunds. ΔS, the soil water storage at sowing time is similar to that at harvest time, which can be ignored. Thus, where Y is the grain yield of maize.
Calculation formula of irrigation water use efficiency 24 (kg m −3 ) is Economic benefits analysis. In order to simply compare the economic benefits of drip irrigation and conventional border irrigation, the annual land rent, machinery, seed, pesticides, insurance, labor, and fertilizer were set at the same price. The net income per hectare of all treatments were calculated by subtracting the planting costs from the total income. The ratio of benefits to costs (B:C) was calculated using the formula in equation 25 : Benefit/cost ratio = gross returns (USD$ hm −1 )/cost of cultivation USD$ hm −1 Statistical analysis. The paper uses 7 years average data. All data were statistically analyzed using SPSS 25.0, including one-way ANOVA, multiple mean comparison using the least significant difference (LSD) test (α = 0.05). The figures were prepared via origin 2018 and excel 2016. Duncan's test was performed to conduct multiple comparisons to identify significant differences between the means of different treatments. Differences were considered statistically significant when p < 0.05.

Results
Growth parameters. Drip irrigation affects maize growth index in different degrees. The plant height, leaf area index and SPAD of average DI maize were higher than those of BI. In comparison to BI, plant height at flowering stage of drip irrigation increased by 7.92%, and that at maturity period increased by 5.95% (Fig. 3).
Leaf area index showed that DI was 22.24% higher than BI at flowering stage. At maturity stage, DI was 24.70% higher than BI (Fig. 4). The SPAD of drip irrigation increased by 3.82% and 3.65% compared with BI at flowering stage and maturity stage (Fig. 5). In general, different irrigation methods had great influence on plant height and Dry matter accumulation. Irrigation methods significantly affected the biomass accumulation of maize at flowering and maturity stages (p < 0.05). In comparison to BI, the reproductive organs biomass of drip irrigation increased by 11.61%, the stems biomass of drip irrigation increased by 8.79%, the leaves biomass of drip irrigation increased by 14.31%, and that the total biomass increased by 10.20% at flowering stage, respectively (Fig. 6). Dry matter accumulation of maize at maturity stage is shown in Fig. 7. The reproductive organs biomass under DI was higher than BI by 5.78%, the leaves biomass increased by 8.17% the stem biomass increased by 8.55% and total biomass increased by 6.75%, respectively. The reproductive organs, leaves, stems and total biomass of maize at maturity stage were higher than those of BI. Table 4 demonstrate that, with the exceptions of row number per ear, drip irrigation significantly influenced the maize yield and their components. It can be seen that the yield of maize DI was significantly higher than that under BI. The average yield of maize DI was 1644.51 kg hm −2 higher than that under BI, and the increasing rate was 14.39%. In terms of yield structure, ear diameter, kernel  www.nature.com/scientificreports/ number per row, row number per ear and 1000-grain weight showed that drip irrigation was greater than conventional border irrigation, and yield components increased significantly by 2.69%, 8.97%, 2.84% and 7.87%. Table 5 demonstrate that the irrigation methods significantly influenced the biomass transfer and related indicators. The dry matter translocation of DI was 27.44% higher than that of BI. The dry matter transfer efficiency of DI was 59.22-85.04%, and BI on was 49.72-75.63%. The dry matter transfer efficiency of DI was 13.97% higher than that of BI. The dry matter contribution of DI was 7.85% higher than that of BI. In general, drip irrigation was superior to conventional border irrigation in dry matter translocation, dry matter transfer efficiency, and grain contribution, which was more beneficial to improve maize yield. Economic benefits. After deducting the total cost, the net income of DI is significantly higher than BI (Table 7). 7-year gross cost based on the same criteria. Gross cost of BI is higher than that of DI by 3.89%. In comparison to BI, gross return, net returns and benefit/cost ratio (B:C) of DI increased by 18.50%, 60.90% and 22.88%. The net economic returns were calculated by subtracting the inputs from the outputs. The inputs include land-leasing costs, seeds, chemical fertilizers, pesticides, machinery, and labor. Drip irrigation costs less than conventional border irrigation 91.41 USD$ hm −1 , net income more than 756.58 USD$ hm −1 .   www.nature.com/scientificreports/

Discussion
Effects of irrigation methods on yield and growth indexes of maize. Compared with conventional border irrigation, drip irrigation has the characteristics of short irrigation cycle 26 and moderate soil moisture obvious dry-wet interface 27 , which is conducive to the growth of maize. Drip irrigation promotes maize growth and increases yield compared with conventional border irrigation. This study showed that compared with conventional border irrigation, drip irrigation increased the average total biomass by 10.20% and 6.75% at flowering and maturity stages, and increased the yield by 10.67%. Sandhu et al. 28 found that maize and wheat under drip irrigation system showed significant grain yield increase of 13.7% and 23.1% compared to furrow irrigation, respectively. Xu et al. 29 found the lowest grain yield from the rainfed maize, whereas the drip irrigation method increased grain yield by 14% at 40% water saving than conventional border irrigation. Zhang et al. 30 reported that drip irrigation under film significantly increased the biomass of maize compared with traditional irrigation, and the biomass at mature stage increased by 6.90%. Li et al. 31 study found that drip irrigation increased dry matter in growth period and biomass in mature period increased by 4.9-11.1%. The results of previous studies are similar to those of this study. Drip irrigation technologies adopt the advantages of drip irrigation and film mulch, thus creating appropriate crop growth conditions in arable soil layers 32 . Through high-frequency irrigation, drip irrigation slowly applies a small amount of water to the root of the crop, so that the crop is always  www.nature.com/scientificreports/ under better water, avoiding the periodic excessive water and water deficit caused by traditional irrigation 33 . Therefore, drip irrigation is more conducive to maize growth. The results of maize growth and yield in this study are similar to those of previous studies. In sum up, drip irrigation was more beneficial to maize growth and yield increase, the main reasons are: (1) different irrigation methods. Drip irrigation under film changed the water supply site and irrigation frequency, thus affecting the infiltration mode and distribution characteristics of irrigation water, increasing the effective water content in maize root zone, which was beneficial to maize growth and thus increased maize yield. (2) Different irrigation quotas. Many previous studies have shown that the best irrigation quota for maize in northern Xinjiang is about 540 mm, too much or too little is not conducive to the improvement of yield. (3) Different irrigation and fertilization time intervals. The increase of irrigation frequency increased the surface area and weight of the lower root, moved the root outward, increased the volume of ellipsoid, and promoted the growth of maize.
Effects of irrigation methods on WUE of maize. Drip irrigation drips water and fertilizer directly and slowly into the soil of crop roots through high-frequency irrigation 34 , forming ellipsoidal or spherical wet bodies in the root zone, which is beneficial for crops to absorb water from the soil and can effectively reduce deep leakage 35 . Because the water of drip irrigation is mainly distributed in the root zone of maize, it is beneficial to the absorption and utilization of crops, thus improving the water use efficiency 36 . Therefore, drip irrigation has better WUE and IWUE than conventional border irrigation for maize. The WUE of crops is an important index to measure the water absorption and utilization efficiency of crops. This study shows that the average WUE of drip irrigation is 3.01%, and that of conventional border irrigation is 1.96%, and the average IWUE of drip irrigation is 3.38%, and that of conventional border irrigation is 2.14%, and the water production efficiency is increased by 57.90%. The water production efficiency is increased by 53.77%. Xiong et al. 37 studies have shown that intermittent irrigation increases water use efficiency by at least 18.2% compared with conventional irrigation. Rasool et al. 38 found that compared with the furrow irrigation treatment, water savings of 33.4-60.0% were found under drip irrigation treatments. Ghamarnia et al. 39 showed that compared with the local conventional furrow irrigation, the seasonal irrigation water of drip irrigation maize was saved by 36-81% by using different drip irrigation belts and surface treatments, combined with soil and water monitoring. Fonteyne et al. 40 showed that under conventional tillage conditions, drip irrigation water saving 36% than furrow irrigation on average, drip irrigation and conservation agriculture combined irrigation water saving 40% than furrow irrigation on average. Those were consistent with our results. Drip irrigation not only improves the irrigation water use efficiency but also achieves the effect of water-saving irrigation. Significant economic, social and ecological benefits have been obtained by the large-scale popularization and application of drip irrigation technology in northwest China.

Conclusions
Under the condition of basic irrigation amount in northwest China, drip irrigation promoted maize growth, dry matter accumulation and WUE compared with conventional border irrigation, thereby increasing yield. Compared with conventional border irrigation, drip irrigation is a saving water, high yield and high efficiency irrigation method for maize planting in northwest China. The yield of maize under drip irrigation was 14.39% higher than that of conventional border irrigation, the water use efficiency was increased by 43.48-68.09%, the irrigation water use efficiency was increased by 47.63-70.60%, and economic efficiency increase of 756.58USD$ hm −1 . Drip Table 7. Economic analysis between drip irrigation and conventional border irrigation for maize (Amount in USD$ hm −1 ). www.nature.com/scientificreports/ irrigation become a more effective measure for sustainable agricultural development in the future, which has cut down on irrigation water about 180 mm.

Data availability
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.