Drip Fertigation Improves Maize Yield, Resource Utilization, and Economic Benefits by Increasing Light Interception Under Dense Planting in Southwest China

Abstract

ABSTRACT

Seasonal drought and traditional water‐fertilizer management limit the increase in the grain yield of summer maize in Southwest China. Drip fertigation mode (HM) can effectively improve crop yields. However, research on drip fertigation has not been conducted in Southwest China. A 2‐year field experiment about HM was carried out with the traditional water‐fertilizer management mode (FM) as control. The plant densities were 5.25 × 10⁴ plants ha⁻¹ and 8.25 × 10⁴ plants ha⁻¹ in 2022 and 6.00 × 10⁴ plants ha⁻¹ and 9.00 × 10⁴ plants ha⁻¹ in 2023. The effects of HM on the aboveground biomass, leaf area index, yield, and resource utilization rate of summer maize were studied. Compared with the FM treatment, the HM treatment significantly increased the yield (25.18%), aboveground biomass (25.58%), leaf area index (34.87%), and leaf area duration (29.60%). HM optimized the canopy structure with an 11.05% improvement in light transmission at the top and a significant 61.32% increase in cumulative light radiation interception per unit area at the bottom of the canopy. The nitrogen partial factor productivity (NPFP), radiation utilization efficiency (RUE), heat utilization efficiency (HUE), and economic benefits of the HM treatment significantly increased by 39.58%, 49.45%, 25.92%, and 32.53%, respectively. In addition, dense planting increased the irrigation water use efficiency (IWUE) by 14.25%. In summary, drip irrigation combined with water and fertilizer can significantly improve maize grain yield, resource utilization efficiency, and economic benefits by increasing light interception in Southwest China. This study will lay a theoretical foundation for filling the relevant research gap in the region.

Introduction

Global warming has led to an increased risk of food production decreases in many countries due to extreme weather events. Specifically, higher temperatures and alterations in precipitation patterns have a substantial impact on agricultural yields (Feng et al. 2021; Hou et al. 2021; Guo, Chen et al. 2022). Maize (Zea mays L.) is the most extensively cultivated crop in China and is particularly susceptible to the impacts of climate change. As a crucial maize-producing hub in China, the southwest region is of paramount importance in ensuring national food security (Rong et al. 2021; Zhou and Duan 2021). However, because maize plants in Southwest China are mainly rainfed, they are easily affected by climate change (Wu et al. 2021). In recent years, extreme weather in Southwest China, such as rising temperatures and reduced rainfall, has put maize crops under drought stress and high-temperature stress during the growth period, resulting in slow plant growth; decreased biomass, grain number, and grain weight; and ultimately reduced maize yield (Luan et al. 2021; Mokhtar et al. 2021).

The maize yield in Southwest China accounts for 16% of the national maize yield, and the cultivated area accounts for 10.91% of the country (National Bureau of Statistics 2021). The reason for the low yield is as follows: On the one hand, this is because of the low planting density. However, increasing the planting density does not significantly increase the yield (Zheng et al. 2020; Zhai et al. 2022b; Liu et al. 2023). An excessively high density and too small plant spacing will lead to crowded plants, poor ventilation of the population, and insufficient absorption of water and fertilizer by rhizomes for plant growth (Xu et al. 2017; Jia et al. 2018). Therefore, the traditional cultivation method is difficult to implement, or the implementation effect is poor due to the dense planting population. On the other hand, due to excess fertilization, the fertilizer utilization rate decreases, and the nitrogen utilization rate is less than 30% (Liu, Lin et al. 2021). Moreover, farmers are accustomed to apply all the fertilizer in the early stage, which easily causes problems such as a lack of fertilizer in the later stage of corn growth, premature senescence of plants, and a decline in soil fertility. At the same time, this method will also lead to environmental pollution (Yao 2021). Therefore, alleviating climate threats and increasing maize grain yield in Southwest China are urgently needed.

By improving agronomic management practices, yield can be significantly increased, and the negative impact of reduced solar radiation on yield can be mitigated (Yang et al. 2021; He et al. 2022; Yu et al. 2022). Fertilization, among which nitrogen is an important nutrient element for crop growth and development, and is an agronomic management measure used to improve yield. Studies have shown that a single application of nitrogen fertilizer can alleviate water stress, and increasing nitrogen application can significantly increase yield by up to 84% (Ma et al. 2021; Guo, Fan et al. 2022; Luo et al. 2023). However, excess nitrogen application did not significantly increase maize yield, nor could it delay leaf senescence, and nitrogen use efficiency also decreased (Hou et al. 2012; Guo, Chen et al. 2022; Hu et al. 2023). Therefore, reasonable nitrogen application can not only increase the biomass, harvest index, and yield of maize but also reduce the deterioration of grain quality (Wang et al. 2020; Zhai et al. 2022a). However, some studies have shown that reducing nitrogen application can also significantly increase maize yield and promote sustainable agricultural development (Hou et al. 2020; Liu, Lin et al. 2021). Increasing planting density is also an agronomic management measure, mainly by increasing biomass and improving water and fertilizer utilization to achieve high maize yields (Wang, Xie et al. 2021; Zhang et al. 2021, 2022). However, excessively close planting does not significantly increase maize yield, and reasonably close planting can effectively increase yield (Yan, Hou et al. 2021; Lai et al. 2022; Shi et al. 2023). In addition, the selection of varieties with longer growth periods can effectively improve the utilization rate of radiation and heat resources and yield (Su et al. 2021). Therefore, reasonably close planting, variety selection, and improvement of nitrogen use efficiency will effectively increase maize yield (Bucagu et al. 2020; Luo et al. 2023).

Maize plants are very sensitive to drought stress, and irrigation can effectively alleviate drought stress and significantly increase the yield (Luan et al. 2021; Xu et al. 2021). However, many studies have shown that excess irrigation does not significantly increase maize yield but also causes waste of water resources, decrease in soil fertility, and nitrogen leaching (Yan, Zhang et al. 2021; Zou et al. 2021). Therefore, reasonable irrigation and improved irrigation methods are necessary for agricultural production. Compared with other irrigation methods (furrow irrigation, flood irrigation), drip irrigation is considered the most effective water-saving irrigation method (Guo, Chen et al. 2022; Ma et al. 2022). Drip irrigation can accurately control the amount of water and reduce water evaporation, thereby significantly increase corn yield and reduce agricultural costs (Rasool et al. 2020; Wang et al. 2021; Yang, Hu et al. 2022). Under drip irrigation conditions, urea can be used as the best nitrogen source for maize (Li et al. 2021). Therefore, a reasonable drip fertigation system can not only provide water and nutrients to crops but also improve the photosynthetic characteristics of dense planting groups and reduce the amount of nitrogen applied while achieving high yield and water use efficiency in maize (Zou et al. 2020; Lai et al. 2022; Shi et al. 2023). To date, drip irrigation water and fertilizer integration technology is becoming increasingly mature and is widely used in Xinjiang, Inner Mongolia, Huanghuaihai, and other regions in China (Zhang et al. 2021, 2022).

Research on drip irrigation water and fertilizer integration technology, including irrigation amount, drip irrigation time, and nitrogen application amount, has improved, and such technology has been accepted by many semiarid and arid areas and is used for crop production (Lai et al. 2022; Mao et al. 2022; Zhang et al. 2023). However, there are few studies on the integration of dense planted crops and drip irrigation in Southwest China. Moreover, there is seasonal drought in the region, especially in the early stage of maize silking, which is vulnerable to high-temperature drought. Therefore, this study aimed to further improve the maize yield and nitrogen utilization rate and alleviate the threat of extreme weather in the region. In this study, the effects of drip irrigation and fertilizer combination on maize growth, grain yield, and canopy characteristics were studied to determine the rationality and feasibility of implementing this technology in this area. The results of this study can provide a theoretical basis and technical reference for coping with extreme weather or drought during the maize growth period in Southwest China.

Materials and Methods

Experimental Site

Field experiments were conducted during the maize growing seasons in 2022 and 2023 at the Mianyang Academy of Agricultural Sciences, Sichuan Province (104°49′ E, 31°23′ N) (Figure 1). The soil in the test field is sandy loam, with the following features: total nitrogen content, 101.9 mg kg⁻¹; available phosphorus content, 24.3 mg kg⁻¹; available potassium content, 24.3 mg kg⁻¹; and organic matter content, 15.0 g kg⁻¹. The annual sunshine duration is 1, 333–1, 353 h, and the mean available cumulative temperature (≥ 10°C) is 3, 987.6°C. During the maize growing season (May to October), the mean annual precipitation is 481 mm, and the mean annual temperature is 25.9°C. The meteorological data collected during the maize growing seasons of 2022 and 2023 are shown in Figure 2.

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Experimental Design

Two cultivation modes were established in 2022 and 2023, namely, the drip irrigation water and fertilizer integration mode (HM) and the traditional management mode (FM). In 2022 and 2023, basal fertilizer (154.13 kg N ha⁻¹, 36.75 kg P ha⁻¹, 52.5 kg K ha⁻¹) was applied in the FM treatment before sowing, and the remaining fertilizer (138.00 kg N ha⁻¹) was top dressed at the jointing stage (6–8 leaves). HM plants were fertilized by a drip irrigation system (Figure 3b). Base fertilizer (86.40 kg N ha⁻¹, 142.50 kg P ha⁻¹, 75.00 kg K ha⁻¹) was applied before sowing, and the remaining fertilizer (201.60 kg N ha⁻¹, 75.00 kg K ha⁻¹) was applied through irrigation during the growth period (8-leaf stage, 12-leaf stage, 5 days after silking, 20 days after silking) according to the nitrogen application ratio of 4-4-3-2.5 and the potassium application ratio of 2-2-1. In 2022, the planting densities of HM and FM were 8.25 × 10⁴ plants ha⁻¹ and 5.25 × 10⁴ plants ha⁻¹, respectively. The plot area was 300 m², and experiments were conducted using the maize variety Zhongdan901 (ZD901). In 2023, the planting densities for HM and FM were 9.00 × 10⁴ plant ha⁻¹ and 6.00 × 10⁴ plant ha⁻¹, respectively. Experiments were conducted using the maize varieties Zhongdan901 (ZD901) and Zhengdan958 (ZD958). The plot area was 60 m², with a total of eight treatments and three replications. The planting methods were wide and narrow alternate planting (with row spacings of 80 and 40 cm, respectively), and drip irrigation tape was applied between narrow rows (Figure 3a). The sowing dates were May 15 and May 25 in the 2 years. Maize was sprayed with 450 mL ha⁻¹ Yuhuangjin at the 6 ~ 8 leaf stage for chemical control, and the pests and weeds were strictly controlled. A sufficient supply of water and fertilizer was ensured in the HM treatment over 2 years.

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Measurements and Calculations

Morphological Traits

Three successive maize plants were selected from each treatment at the silking stage. The plant height and ear height were measured first. When all the leaves were fully expanded, the leaf angle (a), leaf length (l), distance from the base of the leaf to the highest point of the leaf (h), horizontal distance from the highest point of the leaf to the stem, vertical distance from the highest point of the leaf to the base of the plant, horizontal distance from the tip of the leaf to the stem, vertical distance from the tip of the leaf to the base of the plant, length of each internode above the ear and number of leaves above the ear were measured. The ear ratio (Liu et al. 2022) was calculated as$$$ \mathrm{Ear}\ \mathrm{ratio}=\mathrm{Ear}\ \mathrm{height}/\mathrm{Plant}\ \mathrm{height} $$$and the leaf orientation value (LOV) was calculated according to Guo, Chen et al. (2022) and Guo, Fan et al. (2022) as$$$ \mathrm{LOV}=\left(90-\mathrm{a}\right)\times h/l $$$where a is the angle between the stem and leaf, h is the distance from the base of the leaf to the highest point of the leaf, and l is the length of the leaf.

Leaf Area and Biomass

Three uniform maize plants were selected from each treatment at the silking stage and maturity stage. Then, according to the natural growth state of the plants in the population, the bottom layer was used as the benchmark, and 30 cm was used as the layer for slicing. The green leaf area (LA) of each layer was measured by a handheld laser leaf area meter (CID Bio-Science, USA). The plants were then divided into different organs, which were fixed at 105°C for 30 min and then dried at 80°C to a constant weight. The fraction of the leaf area index (Guo, Chen et al. 2022) was calculated as$$$ \mathrm{Leaf}\ \mathrm{area}\ \mathrm{index}={L}_i\times N/S $$$where L_i is the LA of this layer of the plant, S is the land area occupied by the plant (m²), and N is the number of plants in S.

The harvest index (HI) according to Liu et al. (2022) as$$$ \mathrm{HI}=\mathrm{Grain}\ \mathrm{dry}\ \mathrm{weight}/\mathrm{aboveground}\ \mathrm{dry}\ \mathrm{matter} $$$and the leaf area duration was calculated according to Liu et al. (2022) as$$$ \mathrm{Leaf}\ \mathrm{area}\ \mathrm{duration}=1/2\ \left(\mathrm{LA}1+\mathrm{LA}2\right)\times \left(t2-t1\right) $$$where LA1 and LA2 are the leaf areas per plant at times t1 (silking) and t2 (maturity), respectively.

Photosynthetically Active Radiation

After silking, we chose clear days between 11:00 and 13:00 to use a SunScan line quantum sensor (Delta T Devices, UK) to measure the light at 30 cm intervals above the lowermost green leaves. The fraction of intercepted photosynthetically active radiation (fPAR) was calculated by using the PAR values measured above the canopy (PARa) and the transmitted PAR (PARb) measured in the central row below the lowermost green leaves, all with six replicates. The fraction of light transmission was calculated as (Liu, Yang, Liu et al. 2022).$$$ \mathrm{fPAR}=\mathrm{PARb}/\mathrm{PARa}\times 100\% $$$and light interception was calculated as$$$ {\mathrm{fPAR}}_I=1\hbox{--} \mathrm{fPAR} $$$

The light interception per unit leaf area per day (LIPA) was measured as MJ m⁻² day⁻¹ and calculated as$$$ \mathrm{LIPA}={R}_j/{\mathrm{LAI}}_j $$$where R_j and LAI_j are the intercepted radiation and LAI in the jth canopy layer every 30 cm, respectively. The intercepted light energy was calculated from the weather data.

Resource Use Efficiency

The radiation use efficiency (RUE) was calculated as follows (Jia et al. 2018; Zou et al. 2021; Liu, Yang, Guo et al. 2022):$$$ \mathrm{RUE}=q\times {B}_1/\sum R\times 100\% $$$where B₁ is the total biomass at silking, q is the coefficient of biomass converted to heat energy (i.e., 0.0175 MJ g⁻¹ for maize), and ∑R is the total radiation intercepted from sowing to silking in MJ m⁻².

Heat use efficiency (HUE) was calculated according to Liu et al. (2022):$$$ \mathrm{HUE}={B}_2/\sum T $$$where B₂ is the biomass at maturity, ∑T is the effective accumulated temperature (°C·day), represented as a ≥ 10°C active accumulated temperature (°C·day) for maize.

The N partial factor productivity (NPFP) was calculated according to Zou et al. (2021):$$$ \mathrm{NPFP}=\mathrm{GY}/N $$$where GY is the grain yield and N is the nitrogen application rate.

Irrigation water use efficiency (IWUE) was calculated according to (Liu et al. 2022) as$$$ \mathrm{IWUE}=\mathrm{GY}/\mathrm{W}. $$$where GY is the grain yield and W. is the irrigation amount during the maize growth period.

Grain Yield and Yield Components

At physiological maturity, ears from a central 5-m × 2-row area were harvested in each plot, and the grain number per ear was counted. By randomly selecting 10 ears from each plot, the grain number and row number data were recorded. A total of 100 seeds were randomly selected from the seed batches of each plot, and the weight of the seeds was determined using an electronic balance scale. The ear number, grain moisture content, and grain yield were also determined for each plot. The grain yield and kernel weight were expressed at 14% moisture content.

Statistical Analysis

The data were analyzed using Excel 2010 and IBM SPSS Statistics for Windows, version 27.0 (IBM Corp., Armonk, N.Y., USA). At a probability level of 0.05, the least significant difference test was used to determine significant differences. All graphics were created by Origin 2020 (Origin Lab Corporation).

Results

Grain Yield and Yield Components

The yield of HM was significantly greater than that of FM (Table 1). The results of the 2-year data showed that the yield, panicle number, kernel number per ear (KNP), and thousand-kernel weight (TKW) of HM plants were greater than those of FM plants, and the yield significantly increased by 28.63%. In 2022, the yield of ZD901 HM plants significantly increased by 29.40% compared with that of FM plants, KNP and TKW increased by 11.19% and 4.19%, respectively, while the number of ears significantly increased by 61.52%. In 2023, comparing with the low density, the yield of HM and FM under high density increased by 13.66% and 16.42%, respectively. Compared with those in the FM treatment, under 9.00 × 10⁴ plants ha⁻¹, the yields of ZD901 and ZD958 under HM treatment increased significantly, by 20.79% and 23.72%, respectively; KNP increased significantly, by 14.53% and 14.74%, respectively; and the ear number increased significantly, by 6.86% and 9.15%, respectively; however, the TKW of ZD958 increased by only 0.88%, while that of ZD901 increased significantly, by 8.10%. At 6.00 × 10⁴ plants ha⁻¹, the yield of HM significantly increased by 32.84% (ZD901) and 36.82% (ZD958), that of KNP significantly increased by 37.21% (ZD901) and 16.60% (ZD958), that of the ear number significantly increased by 7.26% (ZD901) and 7.93% (ZD958), and that of TKW increased by only 3.57% (ZD901) and 1.44% (ZD958).

TABLE 1 Yield and yield components of HM and FM in 2022 and 2023.

Year	Cultivar	Density (×104 plants ha−1)	Treatment	Ear number (×104 ears ha−1)	KNP	TKW (g)	Yield (Mg ha−1)
2022	ZD901	8.25	HM	7.85 ± 0.15a	457 ± 16a	213.78 ± 3.02a	10.17 ± 0.21a
5.25	FM	4.86 ± 0.32b	411 ± 27a	205.19 ± 11.78a	7.86 ± 0.42b
2023	ZD901	9.00	HM	8.57 ± 0.22a	465 ± 57b	298.73 ± 24.50ab	10.11 ± 0.72a
FM	8.02 ± 0.10b	406 ± 34c	276.34 ± 5.03c	8.37 ± 0.45c
6.00	HM	5.91 ± 0.02c	531 ± 59a	303.78 ± 2.70a	9.44 ± 0.29b
FM	5.51 ± 0.35d	387 ± 12c	293.30 ± 2.55bc	7.63 ± 0.19d
ZD958	9.00	HM	8.59 ± 0.10a	537 ± 38b	258.73 ± 1.62bc	11.77 ± 1.02a
FM	7.87 ± 0.44b	468 ± 18d	256.45 ± 10.34c	8.86 ± 0.54c
6.00	HM	5.99 ± 0.17c	583 ± 19a	269.17 ± 5.71a	9.81 ± 0.37b
FM	5.55 ± 0.25d	500 ± 45c	265.34 ± 13.07ab	7.17 ± 0.52d

Biomass Accumulation and Allocation

At the silking and maturity stages, the biomass in the HM treatment group was significantly greater than that in the FM treatment group (Table 2). The results for 2022 showed that the biomass in the HM treatment group at the silking stage and maturity stage was 114.63% and 41.03% greater than that in the FM treatment group, respectively. In 2023, compared with that in the FM treatment, under the condition of 9.00 × 10⁴ plants ha⁻¹, the biomass of ZD901 and ZD958 plants treated with HM increased significantly by 36.27% and 48.84%, respectively, at the silking stage and increased significantly by 24.43% and 28.80%, respectively, at the maturity stage. Under the condition of 6.00 × 10⁴ plants ha⁻¹, the biomass in the HM treatment at the silking stage significantly increased by 22.89% (ZD901) and 60.32% (ZD958), respectively, and at the maturity stage significantly increased by 21.21% (ZD901) and 16.46% (ZD958), respectively. Analysis of post-silking biomass revealed no significant difference between the HM and FM treatments, except for ZD958 under high-density conditions. The harvest indices were analyzed, the differences between the HM treatment and FM treatment were not significant, and the interannual changes were consistent.

TABLE 2 HM and FM treatments for maize biomass accumulation and distribution in 2022 and 2023.

Year	Cultivar	Density (×104 plants ha−1)	Treatment	Biomass (Mg ha−1)	HI
Silking	Post-silking	Maturity
2022	ZD901	8.25	HM	8.8 ± 0.2a	7.7 ± 0.3a	16.5 ± 0.2a	0.39 ± 0.04a
5.25	FM	4.1 ± 0.2b	7.6 ± 0.5a	11.7 ± 0.3b	0.38 ± 0.01a
2023	ZD901	9.00	HM	13.9 ± 0.3a	13.6 ± 0.8a	27.5 ± 0.4a	0.47 ± 0.02a
FM	10.2 ± 0.3b	11.9 ± 1.9ab	22.1 ± 1.4b	0.49 ± 0.01a
6.00	HM	10.2 ± 0.4b	9.8 ± 1.3bc	20.0 ± 0.7c	0.49 ± 0.01a
FM	8.3 ± 0.2c	8.2 ± 0.1c	16.5 ± 0.1d	0.49 ± 0.01a
ZD958	9.00	HM	12.8 ± 0.2a	11.8 ± 0.7a	24.6 ± 0.7a	0.50 ± 0.03ab
FM	8.6 ± 0.4c	10.5 ± 1.9b	19.1 ± 1.3b	0.48 ± 0.03b
6.00	HM	10.1 ± 0.3b	8.3 ± 0.8b	18.4 ± 0.3b	0.54 ± 0.03a
FM	6.3 ± 0.7d	9.6 ± 1.3b	15.8 ± 0.7c	0.47 ± 0.01b

Morphological Traits and Canopy Structure

Both HM and FM affected the morphological characteristics of maize (Figure 4). The differences between the treatments were small in both FM and HM, so the morphological characteristics of the two varieties were averaged across modes and densities. Compared with those in FM, plant height and ear height in HM significantly increased by 11.98% and 7.07%, respectively. However, ear ratio of the HM plants decreased by only 2.5%, and the difference was not significant. Compared with FM treatment, HM treatment caused a significant decrease of 2.84° in the mean stem-leaf angle above the ear but a significant increase of 3.45 in LOV above the ear, whereas the mean stem-leaf angle below the ear increased by 0.29° and the LOV below the ear increased by 1.79.

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The LA of maize at the silking stage in the HM treatment increased by 2.91% compared to that in the FM treatment and significantly increased by 30.18% at maturity. FM decreased in LA by 60.37% from the silking stage to maturity. However, HM decreased by only 26.77%. Therefore, the greenness of the HM maize leaves improved. The canopy light distribution differed between the two cultivation patterns. At the same canopy height, light transmission was greater in the HM treatment than in the FM treatment. The 30% and 50% light transmission positions were between 90 and 120 cm and 150 and 180 cm in the FM treatment, respectively, while they were between 60 and 90 cm and 120 and 150 cm in the HM treatment. Under FM and HM treatments, the light transmittance at the ear position was 31.84% and 42.89%, respectively, and that at the bottom of the canopy was 14.58% and 16.42%, respectively. At the silking stage and maturity, LIPA accumulation tended to increase from left to right at the different canopy heights. At the silking stage, the ear LIPAs were 9.53 and 9.21 MJ m⁻² day⁻¹ for HM and FM, respectively, and the bottom of the canopy accumulated LIPAs were 24.44 and 15.15 MJ m⁻² day⁻¹, respectively.

Leaf Area Index and Leaf Area Duration

At the silking and maturity stages, the leaf area index and leaf area photosynthetic potential of the HM treatment group were significantly greater than those of the FM treatment group (Figure 5). Compared with that in the FM treatment group, the leaf area index in the HM treatment group significantly increased by 74.92% and 94.30% at the silking stage and maturity stage, respectively (Figure 5A), and the leaf area duration significantly increased by 79.53% (Figure 5G). The results for 2023 showed that compared with those under FM treatment, under 9.00 × 10⁴ plants ha⁻¹, the leaf area indices of ZD901 and ZD958 increased significantly by 17.48% and 22.65%, respectively, at the silking stage (Figure 5B), increased significantly by 15.74% and 32.57%, respectively, at the maturity stage (Figure 5E), and the leaf area duration increased significantly by 16.84% and 24%, respectively (Figure 5H). Under 6.00 × 10⁴ plants ha⁻¹, the leaf area indices of the HM-treated variety ZD901 and variety ZD958 at the silking stage significantly increased by 11.02% and 16.38%, respectively (Figure 5C); at the maturity stage, the leaf area indices significantly increased by 17.56% and 17.96%, respectively (Figure 5F), and the leaf area durations significantly increased by 13.91% and 13.73%, respectively (Figure 5I).

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Resources Use Efficiency

The RUE, HUE, and NPFP in the HM treatment were significantly greater than those in the FM treatment (Figure 6). Compared with those in the FM treatment, in 2022, the RUE, HUE, and NPFP in the HM treatment significantly increased by 94.31%, 40.91%, and 61.74%, respectively, compared with those in the FM treatment (Figure 6A,D,G). Compared with those in the FM treatment, in 2023, the RUE, HUE, and NPFP of ZD901 significantly increased by 39.04%, 24.24%, and 32.05%, respectively, under the condition of 9.00 × 10⁴ plants ha⁻¹, while those of ZD958 significantly increased by 25.30%, 28.86%, and 45.24%, respectively (Figure 6B,E,H). At 6.00 × 10⁴ plants ha⁻¹, the RUE, HUE, and NPFP of the HM-treated variety ZD901 significantly increased by 46.48%, 21.50%, and 35.27%, respectively, while those of the variety ZD958 significantly increased by 62.08%, 16.47%, and 31.26%, respectively (Figure 6C,F,I). In addition, the IWUE of ZD958 significantly increased by 20.27%, while that of ZD901 increased by only 7.85% under the different planting densities (Figure 6J,K).

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Cost–Benefit Analysis

According to the economic benefit analysis, in 2022, the economic benefit of the HM treatment increased by 27.17% compared with that of the FM treatment (Table 3). The results for 2023 showed that the economic benefit of the HM treatment was 38.79% greater than that of the FM treatment.

TABLE 3 Economics of HM and FM treatments in 2022 and 2023.

Year	Treatment	Cost input (Yuan ha−1)	Output (Yuan ha−1)	Economic benefit (Yuan ha−1)
Fertilizer inputs (Yuan ha−1)	Other expenses (Yuan ha−1)	Total (Yuan ha−1)
2022	HM	2400	13,812	16,212	30,510	14,298
FM	2494	9843	12,337	23,580	11,243
2023	HM	5435	10,653	16,088	26,735	10,627
FM	3293	9837	13,130	20,820	7657

Discussion

Due to climate warming, extreme weather, especially high temperature and drought, occurs frequently in Southwest China and significantly affects the growth and development of maize and greatly increases the risk of maize yield reduction (Xu et al. 2017; Donfack et al. 2022). Drought stress will reduce the yield of rainfed maize, and irrigation can effectively alleviate the loss of yield (Leng 2021). In this study, HM significantly increased maize yield (Table 1), which was consistent with the results of Leng (2021). The KNP and TKW are the key factors affecting yield (Gao et al. 2020; Yang, Liu et al. 2022). However, heat stress strongly impacts the growth of summer maize (Wei et al. 2020; Shao et al. 2021). Shao et al. (2021) showed that under high-temperature stress, the bald tip of maize ears increased and the KNP decreased significantly. This may be due to severe heat stress destroying anther structure, reducing the activity of pollen, affecting the development of maize ears, and ultimately affecting the yield of maize (Wei et al. 2020; Shao et al. 2021). In this study, the KNP and TKW of HM plants were significantly greater than those of FM plants (Table 1), because drip fertigation alleviated heat stress and water stress and met the nutrient supply requirements during the maize growth period (Wang et al. 2020; Liu, Lin et al. 2021; Guo, Fan et al. 2022). Therefore, compared with FM treatment, HM treatment can effectively increase maize yield and alleviate climate stress.

Dry matter accumulation is an important factor determining maize grain yield (Zhai et al. 2022a). Liu et al. (2023) showed that reasonably close planting influenced dry matter accumulation and the HI of maize, especially under drip irrigation (Zheng et al. 2020; Wang et al. 2022; Liu et al. 2023). In this study, the biomass of HM plants was significantly greater than that of FM plants (Table 2). However, the difference in HI between the two groups was not significant. According to Ming et al. (2022), high temperature and waterlogging stress may affect the growth and development of maize (Ming et al. 2022). A study by Tollenaar et al. (2006) revealed that these effects may be caused by close planting (Tollenaar et al. 2006). In this study, in 2022, the maize growth period underwent successive waterlogging and high-temperature conditions, and only high-temperature conditions occurred in 2023. Therefore, there was no significant difference in the harvest indices between HM and FM plants. Dry matter accumulation after anthesis may influence maize yield (Wang, Xie et al. 2021), which was inconsistent with the results of this study. Wang et al. (2021) showed that drip irrigation could increase dry matter accumulation after anthesis, which was conducive to the transport of photosynthetic products to grains, thereby increasing maize yield (Wang, Xie et al. 2021). However, the yield of HM plants was significantly greater than that of FM plants in this study, and the trend of dry matter accumulation after anthesis was inconsistent (Table 2). In 2022, the difference between the two was not significant, and only the variety ZD958 (9.00 × 10⁴ plants ha⁻¹) had a significant difference in 2023. This may be due to the continuous high temperature decreasing the dry matter accumulation time (Ming et al. 2022). Therefore, the increase in maize yield in this study mainly depended on the optimization of irrigation and fertilization and the increase in planting density.

Close planting affects the leaf area index of maize (Xu et al. 2017). Hou et al. (2012) showed that drip irrigation could effectively promote the growth and development of maize leaves, and excessive nitrogen application affected the functional period of the leaves (Hou et al. 2012; Qi, Hu, and Song 2020). In this study, dense planting significantly increased the leaf area index, and that of HM plants was significantly greater than that of FM plants at the same density. Therefore, HM treatment, which has reduced nitrogen fertilization, is beneficial to the growth and development of maize (Figure 5). Fan et al. (2020) showed that the effect of drip irrigation on the leaf area index was not significant (Fan et al. 2020), which was inconsistent with the results of the present study. This may be due to the combined stress of high temperature and drought during the growing season of maize in this experiment, so irrigation had a significant effect on the leaf area index. Drip fertigation may affect plant height and ear height (Fan et al. 2020; Liu, Liu et al. 2021). In this study, both the plant height and ear height of HM were significantly greater than those of FM. However, for the ear ratio, the difference was not significant (Figure 4). Plant canopy structure and planting density affect light distribution and radiation interception (Li et al. 2018; Liu, Yang, Liu et al. 2022). In this study, compared with FM treatment, HM treatment improved canopy structure, decreased the leaf pinch angle on the ear, increased the leaf orientation value, and increased light transmission at the ear as well as light radiation interception at the bottom. This indicates that HM has a greater effect on maize plant height, ear height, and height of the upper leaves of the ear to receive more light radiation.

Given the shortage of water resources and the excess application of fertilizer, the coordinated supply of water and fertilizer is an effective way to improve the yield and utilization rates of water and fertilizer (Qi, Hu, and Liu 2020; Yan, Zhang et al. 2021). Guo, Chen et al. (2022) and Guo, Fan et al. (2022) showed that drip irrigation could effectively improve the water and fertilizer use efficiency of maize compared with traditional water and fertilizer management methods (Fan et al. 2020; Rasool et al. 2020; Guo, Chen et al. 2022), which was consistent with the results of this study. Zou et al. (2021) showed that rational close planting and reduced irrigation were beneficial for improving the water use efficiency of maize (Wang, Xie et al. 2021; Zou et al. 2021; Zhang et al. 2022), which was consistent with the results of this study. In addition, the selection of varieties with longer growth periods can effectively improve the utilization rate of crop radiation and heat resources (Su et al. 2021). In this study, the RUE and HUE of ZD901 were greater than those of ZD958 (Figure 6). Through the analysis of economic benefits, this study was consistent with the results of Fan et al. (2020), and HM significantly outperforms FM (Fan et al. 2020). Therefore, drip fertigation (HM) can effectively improve the yield, resource utilization, and economic benefits of maize.

The duration of drought in Southwest China is mainly concentrated in summer and autumn, and the number of droughts has shown an increasing trend, which has a great impact on crop production (Tan et al. 2020; Zhi et al. 2021). In addition, there is a clear seasonal drought in the region, with more rainfall occurring in the later stage, and fertilizer easily lost, resulting in a low maize yield (He et al. 2024). In 2022, Southwest China suffered from extremely high temperatures and drought, resulting in crop yield reductions or even no yield (Sun et al. 2022). However, the integration of dense planting, water and fertilizer increased the yield by 20%–30% in this region (Table 1), and the efficiency of water, fertilizer, light, and temperature use increased significantly (Figure 6), which was highly important for the region to cope with seasonal drought and increase yield to ensure food security.

Conclusions

Fertilization and dense planting can increase maize yield, but traditional irrigation and fertilization methods are less effective in dense planting groups in Southwest China. This study revealed that drip fertigation with dense planting significantly improved maize grain yield, resource utilization efficiency, and economic benefits by increasing the light interception, which will play an important role in the future green and sustainable development of agriculture, as well as in coping with extreme weather or drought during the maize growth period.

Author Contributions

Li Song: conceptualization, date curation, formal analysis, methodology, writing – original draft. Guangzhou Liu: investigation, writing – review and editing. Yunshan Yang: investigation, resources. Xiaoxia Guo: investigation, resources. Hua Zhang: investigation, resources. Tingqi Lu: investigation, resources. Chunyan Qing: resources. Dan Hu: resources. Shaokun Li: conceptualization, supervision, resources, project administration. Peng Hou: conceptualization, resources, investigation, writing – review and editing.

Acknowledgments

This research was supported by the National Key R&D Program of China (2023YFD1900603. 2023YFD2301703), the National Natural Science Foundation of China (32172118), the Central Public-interest Scientific Institution Basal Research Fund (No. CAAS-ZDRW202418), the Agricultural Science and Technology Innovation Program (CAAS-ZDRW202004), and the Talent project of key laboratory for crop improvement and regulation in North China (NCCIR2023RC-4).

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

References

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