Effects of Equivalent Substitution of Chemical Nitrogen Fertilizer with Straw-Derived Nitrogen on Water Consumption Characteristics of Maize Stages

Abstract

This investigation examines the effects of straw-based nitrogen fertilization on soil hydrological properties and biomass partitioning in maize under arid zone conditions. A biennial field investigation was conducted during the 2016–2017 cropping seasons, with an equal nitrogen content of 225 kg ha⁻¹, and a total of 5 treatments, 100% fertilizer nitrogen (CK), 25% straw nitrogen + 75% fertilizer nitrogen (S25), 50% straw nitrogen + 50% fertilizer nitrogen (S50), 75% straw nitrogen + 25% fertilizer nitrogen (S75), 100% straw nitrogen (S100). The data demonstrated that in 2017, in comparison with CK, the soil water storage in the 0–60 cm soil layer of S25 and S50 in the large trumpet stage (V12) increased significantly by 23.32% and 25.14% (p < 0.05), respectively. In the two-year experiment, stratified moisture reserves (0–200 cm) in different treatment groups exhibited a fluctuating pattern characterized by successive increase-decrease-increase transitions along the soil profile, and overall S25 and S50 were larger than CK. In 2016, the biomass accumulation of the S50 treatment at the maturity stage (R6) was the highest, which increased by 18.11% and 19.49% compared with the CK and S75 (p < 0.05), respectively. There was statistical parity in water use efficiency between treatments. Soil moisture retention capacity of 180–200 cm soil was positively correlated with yield at the jointing (V6) and maturity (R6) stages, and soil water storage of 160–180 cm soil was positively correlated with yield at the tasselling stage (VT). Water consumption during the presowing–to–jointing phase demonstrated the strongest correlation with final grain yield. In summary, the S25 treatment in this experiment significantly enhanced the optimization of soil hydrological properties, increasing soil moisture storage, fully utilizing soil moisture, increasing dry matter accumulation in each growth period of maize, and replacing chemical nitrogen fertilizer with 25% of straw equivalent N fertilizers was beneficial to soil moisture storage.

1. Introduction

Water resources shortage has seriously constrained the enhancement of agricultural productivity levels in the dry zone of China [1]. Shanxi Province, located in the eastern part of the Loess Plateau, is a typical mountainous plateau covered by loess and a typical dry farming area [2]. The efficient use of limited moisture resources is the main problem facing agricultural production in this region [3]. Soil moisture status is a key factor in determining the growth of crop roots, and has a decisive impact on crop growth and development and yield [4]. It is an important task of dryland agriculture research to improve soil hydrological regulation potential through water conservation and release dynamics by fertilizing soil fertility, collecting rain and storing moisture, and reducing the ineffective evaporation of soil moisture [5,6]. Nitrogen is an essential element for crop growth [7], and excessive nitrogen application not only leads to the decline of crop yield and quality but also causes waste of resources and environmental pollution [8,9]. China is a country with abundant crop straw [10], and with the improvement of agricultural mechanization, straw re-turning has been widely recognized as an important way to utilize crop straw [11]. Straw improves soil water storage and holding capacity, protects surface soil from runoff and erosion, reduces total leaching, improves soil drought resistance, and the addition of pulverised straw has a positive effect on intercepting and storing soil water, increasing soil moisture content, and contributing to coping with climate change in arid and semi-arid regions with heavy rainfall and long dry periods [12].

At present, straw returning has become one of the important means to improve soil structure and improve soil water retention capacity and hydrological regulation potential [13,14]. Straw returning and nitrogen fertilizer management are critical strategies for enhancing crop productivity in sustainable farming systems. On the one hand, straw returning can enhance the physical and chemical attributes of the soil remarkably, increase soil microbial activity, and play a role in fertilizing soil [15,16]. In contrast, it can stimulate root development in crops [17], delay leaf senescence, and increase plant dry matter accumulation, which is conducive to maintaining crop yield [18].

Straw incorporation represents an efficient agricultural practice that enhances resource utilization efficiency and promotes sustainable farming systems [19]. Straw amendments enhance soil organic carbon accumulation, optimize soil structural stability, and elevate nutrient availability in agricultural soils [20]. Straw returning was beneficial to the formation of soil aggregate structure and increased the content of stable aggregates (>0.25 mm) [21]. Prolonged straw incorporation significantly decreases soil compaction while enhancing overall soil porosity [22]. Crop straw returning can improve soil structure quality, improve permeability and saturation water conductivity, and minimize soil infiltration resistance [23]. The integrated practice of subsoiling with straw residue incorporation within the wheat–maize double cropping system significantly enhanced soil hydrological properties (water retention capacity and infiltration characteristics), improved soil structural quality (reduced bulk density and increased total porosity), and boosted both soil carbon sequestration and crop productivity [24]. In two field trials conducted in Denmark, where spring barley straw and residues were burned or incorporated into the soil annually for 18 years, annual straw return increased soil organic carbon by 5% and total nitrogen by about 10% [25]. Exclusive straw application elevates the soil C:N ratio, yet its slow decomposition kinetics may limit early-stage crop nutrient availability. Integrated straw–nitrogen fertilization optimizes the C:N balance, enhancing nutrient synchronization with crop demand [26]. Using crop straw to replace chemical fertilizers can not only reduce the negative impacts of excessive use of chemical fertilizers but also make resourceful use of straw nutrients, which is of great significance for soil water retention and moisture conservation. Previous studies mostly focused on straw returning or quantitative straw returning with different amounts of chemical fertilizers, and there were few studies on straw instead of chemical fertilizers under the same nitrogen amount.

This investigation systematically examined the vertical distribution dynamics of soil moisture content across two soil profiles (0–60 cm and 0–200 cm) during distinct phenological phases, while concurrently assessing crop water utilization patterns and biomass accumulation characteristics in maize through replicated field experiments. To elucidate the effects of varying fertilization methods on soil moisture and dry matter accumulation in maize aboveground, and to provide a reference for the scientific application of straw returning and nitrogen fertilizer in the process of maize planting in local areas.

2. Materials and Methods

2.1. Site Description

This experiment was set up in the Dongyang Experimental Demonstration Base of Shanxi Agricultural University, Yuci District, Jinzhong City, Shanxi Province (112°40′05″ E, 37°33′22″ N). This area experiences a semi-arid continental monsoon climate within the temperate zone. The yearly precipitation averages 440.7 mm, while the mean annual temperature is 9.8 °C. Additionally, the frost-free period lasts approximately 158 days per year, and the elevation ranges between 750 and 800 m. Soil characteristics of the base soil measured prior to the April 2016 test are shown in

Table 1. Soil physical and chemical properties.

Soil Characteristics	Concentration	Measurement Methods
Organic matter (g kg−1)	13.0	Potassium dichromate oxidation–external heating method
Total nitrogen (g kg−1)	1.3	Kjeldahl method
Total phosphorus (g kg−1)	0.9	Molybdenum Antimony Antimony Colourimetric Method
Total potassium (mg kg−1)	27.1	Flame Photometry
alkali hydrolyzable nitrogen (mg kg−1)	51.2	Alkaline diffusion
Available phosphorus (mg kg−1)	7.7	Sodium Bicarbonate Extraction—Molybdenum Antimony Anti-colourimetric Method
Available potassium (mg kg−1)	176.4	Ammonium acetate extraction-flame photometric method

Note: The above measurements were taken from Analysis for Soil and Agro-Chemistry [27].

.

Table 2. Precipitation during the growing period from 2016 to 2017 (mm).

Year	Presowing–V6	V6–V12	V12–VT	VT–R6	Total Fertility Period
2016	38	188.3	72	21	319.3
2017	25	72.6	176.5	87.5	361.6

Note: Presowing–V6: presowing to the jointing stage. V6–V12: the jointing stage to the large trumpet stage. V12–VT: the large trumpet stage to the tasselling stage. VT–R6: the tasselling stage to the maturity stage.

shows the rainfall in the experimental area from 2016 to 2017.

2.2. Experimental Design

The maize variety tested was “Dafeng 30” (Shanxi Dafeng Seed Industry Co., Ltd., Taiyuan, China), and five treatments were set up in the experiment, which were: 100% fertilizer nitrogen (CK), 25% straw nitrogen + 75% fertilizer nitrogen (S25), 50% straw nitrogen + 50% fertilizer nitrogen (S50), 75% straw nitrogen + 25% fertilizer nitrogen (S75) and 100% straw nitrogen (S100) were all 225 kg ha⁻¹, and the nitrogen application ratio was shown in

Table 3. Nitrogen application ratio for each treatment.

Treatment	Straw Nitrogen		Chemical Fertilizer Nitrogen
	Rate%	Application Amount (kg ha−1)	Rate%	Application Amount (kg ha−1)
CK	0	0	100	225
S25	25	56.25	75	168.75
S50	50	112.5	50	112.5
S75	75	168.75	25	56.25
S100	100	225	0	0

. The amount of straw returned to each treatment is shown in

Table 4. Amount of straw returned to the field for each treatment (kg ha⁻¹).

Treatment	Straw Returned to the Field in 2016	Straw Returned to the Field in 2017
CK	0	0
S25	8561.64	9057.97
S50	17,123.29	18,115.94
S75	25,684.93	27,173.91
S100	34,246.58	36,231.88

. The field test was performed in 3 replicates, 15 plots, each plot area was 30 m² (5 m × 6 m), and the total phosphorus content of each plot (except S100) was kept equal, all of which were 105 kg ha⁻¹. S100 does not use chemical fertilizers. This was calculated as follows: total phosphorus 105 kg ha⁻¹, deducting the phosphorus content carried over from the straw and making up the remaining required phosphorus content with mono ammonium phosphate, and calculating the nitrogen carried over from the mono ammonium phosphate and making up the remaining required nitrogen with urea.

After the autumn harvest in 2015 and 2016, the harvested maize stover was crushed and returned to the field according to the experimental design amount. 2015 straw 6.57 g kg⁻¹ total nitrogen, 2.63 g kg⁻¹ phosphorus. In 2016, the total nitrogen of straw was 6.21 g kg⁻¹ and the phosphorus content was 2.59 g kg⁻¹. Fertilizers were applied to the experimental field before planting in early May in 2016 and 2017. The fertilizers were phosphorus fertilizers and nitrogen fertilizers. The type of nitrogen fertilizer was urea with 46% nitrogen content, and the type of phosphorus fertilizer was monoammonium phosphate with 12% nitrogen content and 61% P₂O₅ content. Maize was planted at a density of 49 500 plants ha⁻¹, and field management was consistent across the plots. There was no irrigation during the whole growth period in 2016 and 2017. The soil was rototilled before sowing. Thinning seedlings was carried out at the seedling emergence stage, and weeded with herbicides applied during jointing.

2.3. Soil Moisture and Calculations

A neutron tube was inserted in the middle of the plot at a depth of 220 cm, the neutron tube was exposed to the ground for 20 cm and covered tightly with a lid to prevent additional water from entering, soil moisture values were determined for the 0–200 cm layer of maize at all periods, with each 20 cm layer divided into 10 layers, and the CPN-503DR HYDROPROBE (2830 Howe Road Martinez, Martinez, CA, USA) was used to measure each layer separately, and the results shown are the readings of the Neutron Meter for that layer of soil. In 2016, the soil moisture from 0 to 200 cm was measured by neutron meter at the jointing stage, large trumpet, tasselling stage, and maturity stage of maize. In 2017, the soil moisture was measured by neutron meter at the jointing stage, and the soil moisture from 0 to 200 cm was measured by soil drill drying method at the large trumpet stage, tasselling stage, and maturity stage, and the soil was taken every 20 cm for one layer.

The formula for calculating soil water storage is as follows [28]:

$$W=\sum \Delta {\theta }_i\times Z_i\times {\displaystyle \frac{10}{100}}$$

where W is the soil water storage capacity (mm), $\Delta {\theta }_i$ is the soil volumetric water content (mm) at soil level i, Z_i is the soil thickness (cm) at level i, and i is the soil level.

Evapotranspiration is calculated as follows [29]:

$$E_T=P+\Delta W+I+K-R$$

where $E_T$ is the evapotranspiration (mm); $P$ is the rainfall of the whole growth period (mm); $\Delta W$ is the difference between the soil water storage capacity at sowing and harvesting (mm); $I$ is the amount of irrigation during the growth period (mm); $K$ is the amount of groundwater recharge (mm); $R$ is the amount of surface runoff (mm); due to the open terrain in the experimental area, the factors such as surface runoff and groundwater were negligible.

The water use efficiency is calculated as follows [30]:

$$WUE=B/E_T$$

where WUE is the water use efficiency [kg (hm⁻² mm⁻¹)], B is the dry matter accumulation in the upper part of the maize field (kg hm⁻²), and $E_T$ is soil water consumption (mm) at different stages.

The formula for calculating daily evapotranspiration is [28]:

$$CD={ET}_i/d$$

where CD is the daily evapotranspiration intensity (mm d⁻¹); ${ET}_i$ is the evapotranspiration during each period of $i$ (mm); and $d$ is the duration of a certain fertility stage of maize (d).

2.4. Dry Matter Accumulation

At the jointing stage (V6), large trumpet stage (V12), tasselling stage (VT), and maturity stage (R6) of maize, the aerial part of 3 plants was taken from each plot, and was dried in an electric blast drying oven at 105 °C for 30 min, and then dried to constant weight at 80 °C and cooled to room temperature. The dry weight is measured with an electronic balance with a capacity of 2000 g and an accuracy of 0.01 g.

2.5. Statistical Analysis

Statistical analysis was performed using IBM SPSS Statistics, version 26.0 (IBM Corporation, Armonk, NY, USA). Data processing and chart creation were conducted using Microsoft Excel, version 2019 (Microsoft Corporation, Redmond, WA, USA).

3. Results

3.1. Soil Water Storage in 0–60 cm Soil Layer at Different Growth Stages of Maize

The root activity of maize was primarily concentrated within the 0–60 cm soil depth, and the variations in soil water storage (SWS) within this layer across different growth stages are illustrated in Figure 1. In 2016, no statistically significant differences in SWS were observed among the alternative treatment groups and the control (CK) at the V6, V12, VT, and R6 stages. However, at the V12 stage, the S50 treatment recorded the highest SWS of 135.62 mm in the 0–60 cm layer, representing a 6.03% increase compared to S100 (p < 0.05).

In 2017, similar trends were observed, with no significant differences in SWS among the treatments at the V6, VT, and R6 stages relative to CK. Notably, at the V12 stage, the S25 and S50 treatments exhibited significant increases in SWS by 23.32% and 25.14% (p < 0.05), respectively, compared to CK. Furthermore, when compared to S100, the S25 and S50 treatments demonstrated substantial improvements in SWS, with increases of 23.44% and 25.26% (p < 0.05), respectively, within the 0–60 cm soil layer.

3.2. Vertical Variation of Soil Water Storage in 0–200 cm Soil Layer During Maize Growth Period

Analysis of the 0–200 cm soil profile in 2016 revealed a shared temporal pattern of water storage dynamics among treatments during maize reproductive stages (Figure 2 and Figure 3). The moisture content followed a triphasic trajectory: an initial upward trend with depth, a mid-profile reduction, and a gradual recovery in deeper layers. Furthermore, the S25 and S50 treatments outperformed CK, demonstrating significantly enhanced water retention capabilities.

During the V6 and V12 stages, soil water storage within the 0–200 cm profile exhibited consistent depth-dependent patterns across treatments. Specifically, moisture content increased from 0 to 40 cm, declined between 40 and 160 cm, and rose again from 160 to 200 cm. A similar trend was observed at the VT and R6 stages, with water storage increasing in the 0–40 cm layer, decreasing from 40 to 100 cm, stabilizing between 100 and 160 cm, and rising again from 160 to 200 cm. Notably, soil moisture in the 120–200 cm layer remained relatively stable throughout the V6, V12, VT, and R6 stages. From V6 to V12, the 0–120 cm soil layer experienced an overall increase in moisture content, likely due to substantial rainfall during this period. Conversely, from VT to R6, water storage in the 0–120 cm layer decreased, potentially reflecting higher water uptake during crop reproductive growth.

In 2017, soil water storage across the 0–200 cm profile displayed consistent trends with depth during the four maize growth stages (Figure 3). Treatments S25, S50, and S75 generally retained higher moisture levels than CK, while S100 showed lower values. At the V6 stage, water storage increased from 0 to 40 cm, decreased between 40 and 160 cm, and rose again from 160 to 200 cm. During the V12 stage, all treatments exhibited a steady increase in water storage with depth across the 0–200 cm profile. At VT, moisture content increased from 0 to 40 cm, declined between 40 and 120 cm, and rose again from 120 to 200 cm. By the R6 stage, the 0–40 cm layer showed increasing water storage with depth in all treatments. For S25 and S50, moisture decreased from 40 to 160 cm and increased from 160 to 200 cm, while in other treatments, it declined from 40 to 180 cm before rising from 180 to 200 cm.

3.3. Soil Water Storage in Different Soil Layers from 0 to 200 cm During Maize Growth Period

Figure 4 and Figure 5 depict the soil water storage (SWS) across the 0–200 cm soil profile at various growth stages. In 2016, the S25 treatment exhibited the highest SWS in the 140–200 cm layer at the V6 stage, with the 180–200 cm sublayer showing significantly greater SWS than other treatments. Specifically, SWS in this sublayer increased by 12.8%, 11.98%, and 12.06% relative to CK, S50, and S100, respectively (p < 0.05). At the V12 stage, no significant differences in SWS were observed among treatments in the 0–40 cm layer, although the S25 treatment recorded the highest soil water content within this depth. In the 40–60 cm layer, the S50 treatment demonstrated a 12.28% higher SWS compared to S100 (p < 0.05). During the VT stage, the S25 and S50 treatments significantly outperformed S100 in the 40–60 cm layer, with SWS increases of 27.46% and 25.04% (p < 0.05), respectively. Additionally, the S25 treatment achieved the highest SWS in the 60–80 cm layer, surpassing S75 and S100 by 43.14% and 43.47% (p < 0.05), respectively. By the R6 stage, the S25 treatment maintained the highest SWS within the 40–120 cm profile. Notably, in the 60–80 cm sublayer, SWS under S25 increased by 27.94% and 42.1% compared to S75 and S100 (p < 0.05), respectively.

In 2017, the soil water storage of the 20–40 cm soil layer treated with S50 was the highest during the V12 period, which was significantly higher than that of the S100 treatment by 27.43% (p < 0.05). The S50 treatment had the highest soil water storage in the 40–60 cm soil layer, which was significantly higher than that of the CK, S75, and S100 treatments by 42.03%, 25.17%, and 55.95% (p < 0.05). The S25 treatment was significantly higher than that of CK, S75, and S100 treatments by 38.18%, 21.78%, and 51.72% (p < 0.05). The S25 and S50 treatments had the highest soil water storage in the 60–80 cm soil layer, which were significantly higher than those of the S100 treatment by 45.41% and 41.32% (p < 0.05), respectively. The S50 treatment had the highest soil water storage in the 80–100 cm soil layer, which was significantly higher than that of the CK and S100 treatments by 46.26% and 39.96% (p < 0.05). At VT, the soil water storage of the 40–60 cm soil layer treated with S25 was the highest, which was significantly higher than that of the CK treatment by 28.42% (p < 0.05). The 60–80 cm soil layer treated with S50 had the highest soil water storage, which was significantly higher than that of S100 treatment by 32.74% (p < 0.05). At R6, the soil water storage of the 20–40 cm soil layer treated with S50 was the highest, which was significantly higher than that of the S100 treatment by 19.49% (p < 0.05). The soil water storage in the 100–200 cm soil layer was the highest in the S25 treatment, 42% higher in the 120–140 cm soil layer than in the CK treatment (p < 0.05), and 62.03% higher in the 160–180 cm soil layer than in the CK treatment (p < 0.05).

3.4. The Characteristics of Evapotranspiration at Different Growth Stages of Maize

Table 5. Evapotranspiration of maize at each growth stage (mm).

Year	Treatment	Presowing–V6	V6–V12	V12–VT	VT–R6
2016	CK	46.02 ab	126.97 a	88.34 a	74.35 a
	S25	43.58 ab	136.94 a	114.48 a	47.49 a
	S50	48.47 a	123.65 a	114.13 a	47.90 a
	S75	43.48 ab	126.05 a	108.75 a	46.86 a
	S100	39.86 b	124.14 a	136.17 a	30.83 a
2017	CK	47.80 a	101.86 a	151.56 a	67.57 a
	S25	47.12 a	65.27 a	178.03 a	38.77 a
	S50	53.12 a	68.30 a	157.12 a	66.29 a
	S75	32.45 a	86.34 a	159.15 a	69.84 a
	S100	33.13 a	86.62 a	153.98 a	66.64 a

Note: Presowing–V6: presowing to the jointing stage. V6–V12: the jointing stage to the large trumpet stage. V12–VT: the large trumpet stage to the tasselling stage. VT–R6: the tasselling stage to the maturity stage. Different letters indicate significant differences between fertilizer treatments at different growth stages (p < 0.05).

shows the evapotranspiration at each stage of maize under different treatments. In the 2016 experiment, the S50 treatment stage had the highest evapotranspiration of 48.47 mm from presowing–V6, and significantly higher than the S100 treatment. The S50 treatment was significantly improved by 21.6% compared to the S100 treatment (p < 0.05). The evapotranspiration was the highest in the S25 treatment stages of the V6–V12 stage and V12–VT stage. In the 2017 experiment, there was no significant difference in evapotranspiration at each stage of maize under different treatments. In the test, the evapotranspiration from V6–V12 in 2016 was the highest. This may be because the rainfall is stronger at this stage, the surface canopy cover is low, and the soil is more ineffective and evaporated.

3.5. Daily Evapotranspiration Intensity at Each Growth Stage of Maize

The daily evapotranspiration intensity of different straw substitution treatments in 2016 and 2017 is shown in

Table 6. Daily evapotranspiration intensity of maize at different growth stages (mm d⁻¹).

Year	Treatment	Presowing–V6	V6–V12	V12–VT	VT–R6
2016	CK	1.40 ab	2.89 a	2.60 a	2.56 a
	S25	1.32 ab	3.11 a	3.37 a	1.64 a
	S50	1.47 a	2.81 a	3.36 a	1.65 a
	S75	1.32 ab	2.86 a	3.20 a	1.97 a
	S100	1.21 b	2.82 a	4.01 a	1.40 a
2017	CK	2.08 a	2.91 a	4.89 a	2.11 a
	S25	2.05 a	1.87 a	5.74 a	1.21 a
	S50	2.31 a	1.95 a	5.07 a	2.07 a
	S75	1.41 a	2.47 a	5.13 a	2.18 a
	S100	1.44 a	2.48 a	4.97 a	2.08 a

Note: Presowing–V6: presowing to the jointing stage. V6–V12: the jointing stage to the large trumpet stage. V12–VT: the large trumpet stage to the tasselling stage. VT–R6: the tasselling stage to the maturity stage. Different letters indicate significant differences between fertilizer treatments at different growth stages (p < 0.05).

. In the 2016 experiment, the daily evapotranspiration intensity of S50 was significantly higher than that of S100 treatment from the presowing to the V6 stage. The S50 treatment was 21.49% higher than the S100 treatment (p < 0.05). In the 2017 experiment, there was no significant difference in daily evapotranspiration at each stage of maize under different treatments.

3.6. Dry Matter Accumulation per Plant

The dry matter accumulation per plant of maize is shown in

Table 7. Dry matter accumulation per plant of maize at each growth stage (g).

Year	Treatment	V6	V12	VT	R6
2016	CK	8.22 ± 3.94 a	112.78 ± 32.57 a	245.86 ± 71.91 ab	307.82 ± 70.41 b
	S25	7.26 ± 3.43 a	103.98 ± 21.6 ab	226.15 ± 62.07 b	337.08 ± 61.16 ab
	S50	6.63 ± 1.85 a	96.16 ± 25.55 ab	254.62 ± 49.26 ab	363.58 ± 58.21 a
	S75	6.01 ± 2.3 a	83.91 ± 21.58 b	244.11 ± 44.8 ab	304.27 ± 34.37 b
	S100	7.76 ± 1.33 a	89.75 ± 25.13 ab	278.74 ± 47.6 a	310.47 ± 28.29 ab
2017	CK	12.17 ± 2.96 a	111.95 ± 18.5 a	255.57 ± 42.64 a	291.54 ± 84.97 a
	S25	8.47 ± 4.5 b	88.44 ± 23.87 b	208.1 ± 69.79 a	278.86 ± 79.76 a
	S50	6.61 ± 2.82 b	89.65 ± 16.79 b	207.57 ± 53.54 a	286.32 ± 58.02 a
	S75	7.46 ± 3.67 b	82.56 ± 13.95 b	212.38 ± 52.74 a	297.79 ± 83.04 a
	S100	6.12 ± 2.81 b	77.43 ± 19.54 b	234.3 ± 57.22 a	288.56 ± 103.89 a

Note: V6, V12, VT, and R6 represented the jointing stage, large trumpet stage, tasselling stage, and maturity stage. Values are mean ± standard deviation. Different letters indicate a significant difference between different fertilization treatments (p < 0.05).

. In the 2016 experiment, there was no significant difference in dry matter accumulation per maize plant in any of the straw replacement fertilizer treatments compared to CK at the maize jointing stage. At the V12 stage, the S75 treatment had a significant 25.6% reduction in maize dry matter accumulation per plant compared to CK (p < 0.05), and the rest of the treatments were not significantly different compared to CK treatment. At the VT stage, the dry matter accumulation per plant of maize in the S25 treatment was significantly reduced by 18.67% compared with S100 (p < 0.05). At the R6 stage of maize, the S50 treatment had the highest dry matter accumulation per maize plant, which was significantly increased by 18.11% and 19.49% compared with the CK and S75 treatments (p < 0.05), respectively.

In the 2017 experiment, there was no significant difference in dry matter accumulation per maize plant in the S25, S50, S75, and S100 treatments compared with CK at the VT and R6 stages. However, the dry matter accumulation of maize per plant was significantly lower in all four straw alternative fertilizer treatments compared with CK at the V6 stage and V12 stage. At the V6 stage, S25, S50, S75, and S100 treatments were reduced by 43.68, 84.11, 63.14 and 98.86%, respectively, compared with CK treatment (p < 0.05). In V12, the S25, S50, S75, and S100 treatments decreased by 26.58%, 24.87%, 35.6%, and 44.59%, respectively, compared with the CK treatment (p < 0.05). The dry matter accumulation per plant of maize at the R6 stage increased first and then decreased with the increase of the proportion of straw replacing chemical fertilizer.

3.7. Dry Matter Accumulation at Different Growth Stages of Maize

The dry matter accumulation of maize at different growth stages is shown in Figure 6. In the 2016 test, the dry matter accumulation of S50 treatment was the highest. The dry matter accumulation was the highest in the CK treatment from presowing to the V6 stage, and there was no significant difference among the other treatments. There was no significant difference in the amount of dry matter accumulation between the V6 to V12 stages, and the CK treatment was the highest. From V12 to VT, the dry matter accumulation of S100 treatment was the highest and significantly different (p < 0.05). Significantly higher than CK and S25 treatments. From the VT to the R6 stage, the S25 showed the highest dry matter accumulation. This is followed by S50 processing. Both treatments were significantly higher than those of the S100. This increased by 249.55% and 243.38%, respectively (p < 0.05).

In 2017, the dry matter accumulation of the S75 treatment was the highest. At the presowing–V6 stage, the dry matter accumulation of CK treatment was the highest, which was significantly higher than that of S100 treatment by 98.8% (p < 0.05). There was no significant difference in dry matter accumulation among the treatments in the V6–V12 stage, and the CK treatment had the highest dry matter accumulation. At the V12–VT stage, the S100 treatment had the highest dry matter accumulation, and there was no significant difference among treatments. The S75 treatment accumulated the highest amount of dry matter at the stage of VT–R6.

3.8. Water Use Efficiency

The water use efficiency of maize at different growth stages is shown in Figure 7. In 2016, there was no significant difference in water use efficiency between different treatments at different growth stages.

3.9. Correlation Between Soil Water Storage and Yield at Each Soil Layer at Different Growth Stages of Maize

The correlation between soil water storage and maize yield at each soil layer during the growth period of maize is shown in

Table 8. Correlation analysis between soil water storage and maize yield at different soil layers.

	Y (V6)	Y (V12)	Y (VT)	Y (R6)
X1	0.151	−0.223	0.491	0.193
X2	0.36	−0.055	−0.165	0.354
X3	0.54	0.048	0.202	0.334
X4	0.617	0.058	0.558	0.385
X5	0.618	0.139	0.363	0.492
X6	0.17	0.335	0.197	0.111
X7	0.317	0.091	0.195	0.099
X8	−0.028	−0.107	0.377	−0.032
X9	0.26	0.392	0.710 *	0.277
X10	0.637 *	0.469	0.315	0.825 **

Note: X1, X2, X3, X4, X5, X6, X7, X8, X9 and X10 represented the soil water storage in the 0–20, 20–40, 40–60, 60–80, 80–100, 100–120, 120–140, 140–160, 160–180 and 180–200 cm soil layers, respectively. Y represented maize yield. V6, V12, VT, and R6 represented the jointing stage, large trumpet stage, tasselling stage, and maturity stage. ** p < 0.01. * p < 0.05.

. At V6, there was a significant positive correlation between the water storage of the 180–200 cm soil layer and yield (p < 0.05). At VT, there was a significant positive correlation between the water storage of the 160–180 cm soil layer and yield (p < 0.05). At R6, there was a significant positive correlation between the water storage of the 180–200 cm soil layer and yield (p < 0.01).

3.10. Correlation Between Evapotranspiration, Daily Evapotranspiration Intensity and Yield Formation

Table 9. Correlation analysis of evapotranspiration and yield at different stages.

	Presowing–V6	V6–V12	V12–VT	VT–R6
Presowing–V6	1
V6–V12	−0.02
V12–VT	−0.148	−0.883 **
VT–R6	−0.148	−0.153	−0.108	1
Y	0.745 *	−0.171	0.066	0.07

Note: Presowing–V6: presowing to the jointing stage. V6–V12: the jointing stage to the large trumpet stage. V12–VT: the large trumpet stage to the tasselling stage. VT–R6: the tasselling stage to the maturity stage. Y represented maize yield. ** p < 0.01. * p < 0.05.

and

Table 10. Correlation analysis between daily evapotranspiration intensity and yield at different stages.

	Presowing–V6	V6–V12	V12–VT	VT–R6
Presowing–V6	1
V6–V12	−0.670 *	1
V12–VT	0.640 *	−0.767 **	1
VT–R6	−0.02	0.207	−0.252	1
Y	0.677 *	−0.163	0.094	0.054

Note: Presowing–V6: presowing to the jointing stage. V6–V12: the jointing stage to the large trumpet stage. V12–VT: the large trumpet stage to the tasselling stage. VT–R6: the tasselling stage to the maturity stage. Y represented maize yield. ** p < 0.01. * p < 0.05.

show the correlation between evapotranspiration, daily evapotranspiration intensity, and yield during the growth stage of maize. As can be seen from Table 6, there is a correlation between evapotranspiration and yield at the maize growth stage. There was a significant positive correlation between yield and evapotranspiration at the presowing–V6 stage (p < 0.05). However, yield was not significantly correlated with the other three stages.

As can be seen from Table 9, there is a correlation between the daily evapotranspiration intensity and the yield. There was a significant positive correlation between yield and daily evapotranspiration intensity at the presowing–V6 stage (p < 0.05). However, yield was not significantly correlated with the other three stages.

4. Discussion

In this experiment, the rainfall in 2016 was relatively high during the V12 period. The volume of straw in the field leads to soil looseness, and most of the rainfall is stored across the topsoil of the cultivated layer, so the soil water storage is higher at the V12 stage. A study [31] showed that straw mulch plus straw return treatment enhanced soil moisture retention content in the 0–40 cm soil layer, and the water content of straw mulch plus straw return surface soil (0–20 cm) was 1.6–10.4% higher than that of straw mulch treatment (p < 0.05). In this experiment, the soil water storage of 0–60 cm soil layer treated with S25 and S50 was higher.

In 2017, the 0–60 cm soil layer under S25 and S50 treatments exhibited a markedly greater water retention capacity compared to the control (CK), suggesting that low-rate equal N straw return practices enhanced soil moisture storage within this depth range. However, no statistically significant variations in soil water storage were observed in the 0–60 cm layer among the treatment groups at the VT and R6 stages. This could be attributed to the completion of straw decomposition, which optimized soil structure and enhanced water retention capacity, resulting in negligible differences between treatments during the later growth period. Soil moisture retention in the 0–60 cm soil layer was significantly greater in S25 and S50 than in CK at the V12 stage in 2017, indicating that the low proportion of equal nitrogen straw return treatment could enhance water retention in the 0–60 cm soil profile; however, no statistically significant variations in soil water storage were observed in the 0–60 cm layer among the treatment groups by the RT and R6 stages. This could be attributed to the completion of straw de-composition, which optimized soil structure and enhanced water retention capacity, resulting in negligible differences between treatments during the late fertility stage. In a trial of straw return and tillage management [32], the treatment of rotary plowing to return straw to the 0–60 cm soil profile yielded higher pre-sowing soil water storage and field evapotranspiration. In farmland, the decomposition rate of straw showed a trend of “fast first and then slow” [33]. In this experiment, straw returning could increase the soil moisture storage of 0–2 m soil layer during the developmental phase of maize, and the soil water storage of straw returning with a low proportion of equal nitrogen content was higher than that of straw returning with a high proportion of equal nitrogen content, which was generally S25> S50> S75 > S100. It may be because the amount of straw reintegrated into the field is small, the straw decomposition rate is higher, and the water consumption of crops in the early stage is less. However, total water use and daily water use intensity exhibited an initial increase followed by a gradual decline, peaking during the mid-growth stages (V12 to VT). Furthermore, the S25 treatment consistently outperformed other experimental plots in retaining soil moisture, with significantly higher water storage observed throughout the 2 m soil profile at all maize growth stages. The S25 and S50 treatments were greater than those of the CK treatment, and the appropriate amount of nitrogen returned to the field such as straw was conducive to water retention capacity and hydrological preservation.

The combination of straw returning and nitrogen fertilizer increased the organic carbon and nitrogen in the soil [34]. In a 10-year positioning experiment [35], different types and different amounts of application of straw amendments significantly promote organic carbon accumulation in arable soils. The incorporation of straw residues significantly elevated soil organic carbon content and stability, primarily through strengthened interactions between organic matter and complexed iron oxides. The incorporation of rotary tillage straw increased the deposition and contribution of dehydrated matter and nitrogen to grain efficiency [36]. The combination of straw returning and nitrogen fertilizer improved crop photosynthesis and allowed maize to accumulate more dry matter [37]. Compared with CK, the dry matter accumulation in the early stage of the growth period was less and the dry matter accumulation in the later stage increased, which may be due to the microbial reproduction and crop competition for soil nitrogen during the early straw decomposition process, which destroyed the soil carbon and nitrogen balance and resulted in reduced dry matter buildup, while the soil nitrogen was balanced after straw decomposition in the later stage to increase the nutritional value of the dry biomass. In the presowing–V6 and V6–V12 stages, the straw substitution approach led to a reduction in dry biomass accumulation when compared to the CK treatment. The deposition of dry matter was the highest in the S100 at the V12–VT stage, which may be caused by the different degradation rates of straw returning to the field.

In the experiment, in the process of maize growth and development, the evapotranspiration of each treatment showed a trend of first increasing and then decreasing. The daily evapotranspiration intensity of maize is related to factors such as sunshine intensity, climate temperature, and rainfall. From the sowing to the V6 stage, the leaf area coverage rate of maize was the lowest, and its evapotranspiration was mainly due to the increase in surface growth, so the daily evapotranspiration intensity of each treatment was smaller. The differences between treatments were not statistically significant. During the V12 to VT stage, the growth rate of maize was significantly accelerated due to the increase in temperature and sunshine intensity, so the evapotranspiration intensity increased significantly, and the daily evapotranspiration intensity was the maximum value of the whole growth period. When maize enters the maturity stage, the sunshine intensity and temperature decrease, the transpiration, evaporation and photosynthesis of maize begin to decrease, the vegetative and reproductive progression of maize tend to stop, and the daily evapotranspiration intensity further decreases.

Nitrogen application to straw under the wheat–maize multiple cropping systems significantly enhanced the crop water productivity in wheat cultivation and maize by 4–7% and 8–11% (p < 0.05), respectively [38]. Straw cover crops increased the water available to plants by 21–22% (p < 0.05) [39]. This experimental investigation revealed comparable water productivity levels between straw-based nitrogen substitution and exclusive chemical fertilization treatments.

5. Conclusions

In this experiment, compared with chemical fertilizer alone, the substitution of nitrogen with straw could markedly enhance the dry biomass buildup per maize plant. Among them, the dry matter accumulation of 50% straw nitrogen instead of chemical fertilizer nitrogen was the largest. Straw-derived nitrogen fertilization demonstrated enhanced soil moisture retention within the 0–60 cm soil profile. Compared to chemical fertilizers alone, the straw substitution treatment exhibited a triphasic trend (increase-decrease-increase) in soil water storage across the 0–200 cm soil profile. The substitution of 25% chemical fertilizer nitrogen with straw nitrogen could enhance soil moisture retention within the 60–160 cm soil profile. In the late growth and development stage of maize, the water use efficiency of 25% straw nitrogen instead of chemical fertilizer nitrogen was the highest. From the perspective of ensuring soil moisture and straw dry matter accumulation, 25% straw nitrogen substitution for chemical fertilizer nitrogen is the most potential way to replace chemical fertilizer with straw nitrogen under this experimental condition.