Single irrigation at the four-leaf stage in the spring optimizes winter wheat water consumption characteristics and water use efficiency

doi:10.21203/rs.3.rs-1745930/v1

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Single irrigation at the four-leaf stage in the spring optimizes winter wheat water consumption characteristics and water use efficiency

https://doi.org/10.21203/rs.3.rs-1745930/v1

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Water scarcity is a major limiting factor for crop production in North China Plain (NCP), which produces the majority of the country's winter wheat (Triticum aestivum L.). The objective of this three-year field study was to see if and when irrigation one-time in spring improves grain yield and water use efficiency. Four sets of irrigation were established at the 3-leaf visible stage (L3) and the L4, L5, and L6 stages. The spike number, 1,000-grain weight, and water consumption increased progressively when irrigation time was delayed, whereas grain yield, grain number, dry matter, harvest, and WUE grew, then dropped, and peaked at L4. The increased grain number can be attributed to the L4's higher daily water consumption and water consumption percentage than the L3, L5, and L6 at the jointing-anthesis stages. L4 had a shorter cumulative period of soil drought stress (37 days), whereas L3, L5, and L6 had 40, 42, and 43 days, respectively. Furthermore, flag leaf senescence was postponed in L4 with a better post-anthesis leaf area index, photosynthetic rate, chlorophyll content, stronger superoxide dismutase activity, and reduced malondialdehyde concentration. As a result, single irrigation at the 4-leaf visible stage optimized water deficit and consumption before and after anthesis, resulting in higher yield and WUE in the NCP.

Wheat (Triticum aestivum L.) is the most widely planted and important cereal grain in the world. Fresh water resource scarcity restricts wheat production in the water shortage areas. Optical irrigation management achieving high yield and high water use efficiency was an effective way to alleviate the contradiction between food demand and water crisis¹.

The average water supply per capita in the world is about 9000 m³, but only 2200 m³ in China. While it is 456 m³ in North China Plain (NCP), one of China's important areas for grain production, which accounts for about 60% of the country's wheat production^2,3. Climate change and increasing food demand, water shortages have become a major challenge to the sustainable development of agriculture in the NCP⁴. The water requirement for wheat in this region is approximately 400–500 mm, but the average rainfall is 50–150 mm, which is insufficient and results in unpredictable wheat growth^5,6. Thus, irrigation is the primary way to enable the growth and development of winter wheat and obtain a higher yield⁷. Groundwater is the main source of irrigation in the region and is applied to winter wheat through surface irrigation⁸. Traditionally, farmers irrigate the winter wheat three to six times, with a total volume that exceeds 300 mm⁹, which significantly reduces the water use efficiency (WUE) of winter wheat^10,11. The groundwater in the North China Plain is severely overdrawn, generating the world's largest groundwater funnel area¹². In this context, crop production has been transformed from high-yield style to water -saving style¹³. The current water-saving and high-efficiency irrigation scheme in this region now is irrigating at the jointing stage and anthesis period, which were sufficient for the production of winter wheat in the NCP^14,15. However, the problem of groundwater overexploitation remains serious. 13×10⁴ ha field was fallowed to reduce irrigation water and mitigate the downward trend of groundwater levels. If the irrigation volume could be reduced further, the fallowe area could be replanted with winter wheat. Therefore, with the likelihood of future reductions in groundwater, the NCP urgently needs to reduce irrigation while maintaining production to further improve the WUE^{16 17}.

Optimizing irrigation schedule is an important measure to improve the winter wheat yield and WUE ^20–22. Limited irrigation is usually defined as an irrigation strategy in which less irrigation water is consumed lower than the total required by the crops, i.e., reducing the number of irrigation times and irrigation amount, which can be considered to save water and increase the WUE^23,25. Limited irrigation optimize wheat canopies and regulate water consumption without causing a severe reduction in yield²⁶. Reducing the frequency of irrigation promotes the development of deep soil roots and the utilization of deep soil water by roots²⁷. The effects of water stress on crops can be avoided by adequate water irrigated during the critical period of water requirement and limited water irrigated when they are most resistant to water deficits²⁸. Water stress on crops can be prevented by irrigating with enough water during critical water-requirement growth phases and irrigating with less water when they are resistant to water shortages²⁹. There has been a substantial amount of research based on single irrigation in the spring, which reached different conclusions; however, they proved that single irrigation generally reduces or maintains the yield while increasing the WUE compared with conventional irrigation^25,30,31. Previous studies on single irrigation in spring were often based on standing stage and jointing stage but there have been few studies on irrigation based on the spring leaf age of wheat²¹.

Drought stress induces a series of physiological and biochemical reactions in plants, and flag leaf senescence is closely related to the degree of drought stress in wheat^32,33.A moderate delay in irrigation time can promote the growth of wheat roots to deeper soil and increase the water absorption of deeper soil, thereby improving the yield, harvest index (HI) and WUE³⁴. Moderate stress improved dry matter transport to kernel, while mild stress at the recovery-jointing stage improved the wheat canopy structure before anthesis and maintained higher post-anthesis photosynthesis³⁵. Controlling soil moisture before jointing not only stimulates wheat root growth but also controls the leaf size and tiller number, reducing the unnecessary consumption of water and fertilizer⁵. The flag leaf is the last senescent leaf and has been considered to be the main contributor to grain filling in wheat, since it serves as a source of photo-assimilates. Simultaneously, photosynthesis by the flag leaf contributes 30–50% of the assimilates used for wheat grain filling. 30–50% of the assimilates come from the photosynthesis of flag leaf during grain filling stage³⁷. As the last senescent leaf, the chlorophyll content, photosynthetic rate and antioxidant enzyme activities could reflect the winter wheat degree of drought stress³⁶. Reactive oxygen species (ROS) produced by drought stress can damage plant calls causing the peroxidation of lipids in cell membranes, and superoxide dismutase(SOD) is an important component of the antioxidant protective enzyme system, which can reduce the toxic effects of ROS on cells³⁸. Malondialdehyde (MDA) is a product of membrane lipid peroxidation that reflects the damage to crop cells under adverse conditions³⁹. The decline in wheat yield is attributed primarily to the reduction in photosynthesis and the acceleration of leaf senescence caused by water stress during grain filling⁴⁰.

In this study, single irrigation was performed based on the spring leaf age of winter wheat. We hypothesized that irrigation at a certain leaf age can optimize the supply of soil water before and after the anthesis of wheat, which not only ensures the formation of spike number and grain number but also delays post-anthesis leaf senescence and increases the dry matter accumulation during grain filling. To test this hypothesis, a three-year experiment with different irrigation periods was conducted, and the leaf area index and dry matter accumulation, post-anthesis leaf photosynthetic rate and chlorophyll content, the activity of SOD, content of MDA, yield and yield components, and the characteristics of water consumption were studied.

Experimental site description

The field experiments were conducted during the 2018–2021 growing seasons at the Malan Experimental Station of the Agricultural University of Hebei, Baoding, China (37°99′N, 115°20′E). The region is located in the semi-humid continental temperate monsoon region with an altitude of 37 m. In the test field, the contents of organic matter, total nitrogen, available potassium and available phosphorus in the topsoil (0–40 cm) were 22.4 g/kg^− 2, 1.26 g/kg^− 2, 125.0 mg/kg^− 2 and 25.8 mg/kg^− 2, respectively. At the beginning of the field test, the soil pH value was 7.6. The meteorological data for the last 20 years had been recorded at the research site (Fig. 1a). The average annual rainfall from 2001 to 2021 was 472.5 mm, including 124.5 mm in the wheat season. We satisfied the daily rainfall and daily mean temperature of the three seasons of winter wheat growth (Fig. 1b). The rainfall in these three years was 85.9, 176.2 and 103.4 mm, respectively.

Experimental design

The experiment adopted a randomized block experiment design. The soil bulk density and field capacity in the 0–200 cm soil layers with 20 cm increments are shown in Table 1. The high-yielding wheat cultivar Shi4366 was used in the experiments, since it is one of the most important and widely planted crops in Hebei Province. The planting density was 3.75*10⁴ plants ha^− 1 with a row spacing of 15 cm.

The wheat was sown on October 10, 2018, October 13, 2019, and October 10, 2020, and the harvest dates were June 8, 2019, June 9, 2020, and June 7, 2021. Four irrigation periods at the 3-leaf visible (L3) stage, 4-leaf visible (L4) stage, 5-leaf visible (L5) stage and 6-leaf visible (L6) stage were established with 90 mm irrigation level. The growth of wheat in the field during the irrigation period is shown in (Fig. 2). The irrigation method was micro-spray irrigation, with a spraying height of 0.6 m and a spraying range of 1.2 m. The base fertilizer, including 120 kg N ha^− 1, 112.5 kg P₂O₅ ha^− 1 and 112.5 kg K₂O ha^− 1, was applied with a rotary cultivator before sowing. A rate of 120 kg N/ha^− 1 of urea (46% N) was completely dissolved in a fertilization device and applied as topdressing together with the irrigation water. Each treatment was repeated three times in three replicates for a total of 15 plots. Each test plot was composed of 60 rows of wheat. The row spacing was 15 cm. Each treatment was conducted in three test plots with area of 20 m². The dates of sowing, the jointing stage, anthesis stage, harvest stage and irrigation times for the three seasons are listed in detail in Table 2.

Table 1

The soil bulk density and field capacity in 0–200 cm soil layers in the experimental plots.
Soil layer (cm)	0–20	20–40	40–60	60–80	80–100	100–120	120–140	140–160	160–180	180–200
Bulk density (g cm^− 3)	1.34	1.59	1.55	1.60	1.60	1.59	1.60	1.60	1.59	1.58
Field capacity (%)	35.2	35.3	37.6	37.7	38.0	35.9	35.0	35.0	33.2	34.6

Table 2

Dates of sowing, jointing stage, anthesis, and harvest under different treatments in the 2018–2021 growing seasons of winter wheat.
Year	Treatment	Dates of Sowing	Dates of Jointing Stage	Dates of Anthesis Stage	Dates of Harvest	Irrigation Date
2018–2019	L3	October 8, 2018	April 5, 2019	May 4, 2019	June 6, 2019	March 25, 2019
	L4	October 8, 2018	April 3, 2019	May 2, 2019	June 8, 2019	April 3, 2019
	L5	October 8, 2018	April 3, 2019	May 2, 2019	June 7, 2019	April 11, 2019
	L6	October 8, 2018	April 3, 2019	May 1, 2019	June 5, 2019	April 17, 2019
2019–2020	L3	October 13, 2019	April 3, 2020	May 2, 2020	June 6, 2020	March 22, 2020
	L4	October 13, 2019	April 1, 2020	April 30, 2020	June 7, 2020	March 30, 2020
	L5	October 13, 2019	April 1, 2020	April 30, 2020	June 7, 2020	April 8, 2020
	L6	October 13, 2019	April 1, 2020	April 29, 2020	June 4, 2020	April 15, 2020
2020–2021	L3	October 10, 2020	April 5, 2021	May 4, 2021	June 5, 2021	March 24, 2021
	L4	October 10, 2020	April 5, 2021	May 2, 2021	June 7, 2021	April 3, 2021
	L5	October 10, 2020	April 5, 2021	May 2, 2021	June 7, 2021	April 11, 2021
	L6	October 10, 2020	April 5, 2021	May 1, 2021	June 5, 2021	April 17, 2021

Sampling and measurements

Soil water

The content of volumetric water at each 20 cm soil layer to a depth of 0-200 cm (Trime Pico 64 Portable Soil Moisture Meter, TDR, EMIKO, GmbH, Bochum, Germany) was measured at the sowing stage, returning green stage, jointing stage, anthesis stage and every five days from the 3-leaf unfolding stage to maturity. The water consumption (ET) was calculated using the following equation:

$${{\rm E}{\rm T}}_{1-2}=\varDelta S+{\rm M}+{\rm P}{\rm O}+{\rm K}$$

where ${{\rm E}{\rm T}}_{1-2}$ is the phase water consumption (mm); $\varDelta S$ is the change in the soil water storage in the 2 m soil body during the wheat growth period (mm) (i.e., the soil storage water consumption); ${\rm M}$ is the irrigation amount (mm) for the period; ${\rm P}{\rm O}$ is the effective precipitation (mm), and ${\rm K}$ is the groundwater replenishment amount (mm) for the period. The groundwater depth in the experimental site is lower than 25.8 m, and the K value can be ignored.

The water consumption percentage for a given stage (CP) is the ratio of the water consumption amount of that stage (CA) to the total evapotranspiration (ET). The daily water consumption (CD) is the ratio of the number of growing days at this stage to the water consumption amount of that stage.

The water use efficiency (WUE, kg/m³) was calculated as follows:

$$WU{\rm E}={\rm Y}/{\rm E}{\rm T}$$

where Y is the grain yield (kg/ha^− 1).

Dynamics of winter population

Tillers were marked from the appearance of the first tiller. The newly initiated tillers of each plant were checked and tagged every 5 days. After jointing, the tagged plants were selected and separated based on the tiller positions for measuring. In this study, the main stem was considered to be O, and the primary tillers that grew from the true leaf axillary of O were considered to be I, II, III, and IV among others. Conversely, I-p, I-1, and I-2 among others were used for the secondary tillers that grew from the axillary of the true leaf of the primary tillers ^24,41.

The number of tillers (stems) per square meter was investigated at the wintering stage, returning green stage, jointing stage, heading stage, anthesis stage, anthesis and maturity.

Leaf area index (LAI) and Dry matter accumulation (DM)

The green leaf area was measured every 5 days from the anthesis stage to maturity (i.e., 0, 5, 15, 20, 25, and 30 days after anthesis) using an Li-3100 area meter (LICOR, Inc., Lincoln, NE, USA), and the green leaf area index (LAI) was calculated.

To determine the dry matter accumulation, plants with an area of 0.15 m² at ground level were sampled at anthesis and maturity, respectively, and all the plant samples were oven-dried at 75°C to a constant weight. The HI was calculated as the ratio of grain yield (GY) to the total aboveground DM accumulated at maturity.

Leaf chlorophyll content and photosynthetic rate

To determine the chlorophyll content (a and b) of the flag leaf from anthesis to maturity, 20 flag leaf samples were randomly collected from each experimental plot every 5 days (i.e., 0, 5, 15, 20, 25, and 30 days after anthesis) and stored at -25°C until the biochemical assays were performed. The leaf samples were chopped on ice, quickly weighed (200 mg) and extracted with 95% ethanol for 48 hours in the dark. The extract was measured at A649 and A665 with a spectrophotometer.

The wheat flag leaves were sampled at 0, 5,15, 20, 25, 26, and 30 d after the anthesis stage. The photosynthetic rates (Pn, µ mol CO₂ m^− 2 s^− 1), transpiration rate (Tr, mmol CO₂ m^− 2 s^− 1) and stomatal conductance (Gs, mol m^− 2s^− 1) were measured using a Li-6800 Portable Photosynthesis System (LI-COR Biosciences).

Antioxidant enzyme activities and the content of malondialdehyde

Flag leaves were collected at 10:00 every 10 days from anthesis. The flag leaves were ground in 5 mL of extraction buffer (50 mM potassium phosphate + 0.4% polyvinylpyrrolidone [PVP], pH 7.0) on dry ice. The extract was centrifuged at 10000 g for 15 min at 4°C. The supernatant was collected to measure the content of MDA and activity of SOD as described by ⁴².

Grain yield and yield components

To determine the final grain yield, the spikes were counted in six 1 m central rows of each plot before harvest. The number of grains per spike was determined by calculating the number of grains per spike from 50 plants that were randomly selected from each plot before harvest. During the physiological maturity of wheat, 3 m² of wheat plants were harvested from each plot and threshed to determine the grain yield (13% moisture content). The weight of 1,000 grains (TGW, 13% water content) was calculated by weighing 1,000 grains in each sample and repeating the average three times.

Statistical analysis

Statistical analyses were performed using SPSS 19.0 (SPSS, IBM, USA). The treatment effects were investigated studied by standard split-plot design analysis method. Significant differences were identified using a one-way analysis of variance (ANOVA) and least significant difference (LSD) tests at 95% or 99% confidence levels. All the figures were created using Origin Pro 2019 (Origin Lab Corporation, Northampton, MA, USA) or GraphPad Prism 9.0 (GraphPad Software, Inc., San Diego, CA, USA). A correlation analysis was performed using R software (R 4.0.4).

Grain yield, yield components and WUE

In this study, the grain yield, spike number, grain number and 1,000-grain weight (TGW) of winter wheat were significantly affected by the year (Y) and irrigation time(I) (Table 3). The grain yield and TGW were also significantly affected by the interaction of year and irrigation time. The spike number first increased and then decreased with the delay in the irrigation time and peaked in the L4 treatment. Compared with L4, the average spike number in L3, L5 and L6 was reduced by 4.6%, 9.9% and 17.2%, respectively. However, the grain number decreased with the delay of irrigation time, showing that L4, L5, and L6 were 3.9%,7.8% and 16.5% lower than L3, respectively. The grain number in L6 was significantly lower than that in the other treatments, while the difference between L3, L4 and L5 was not significant. However, the TGW significantly increased with the delay of irrigation time. Compared with L3, for every postponement of irrigation for one leaf age, the average TGW increased by 1.9 g, 2.4 g, and 2.9 g.

Compared with 2020–2021, the grain yield of 2018–2019 and 2019–2020 was significantly reduced. The annual difference in grain yield was attributed to rainfall and other meteorological conditions. The lower precipitation after anthesis in 2018–2019 resulted in a lower TGW, and the low temperature in the spring of 2019–2020 resulted in a lower spike number (April 9–10). Despite the annual difference in GY, the highest yield during the three growth seasons was obtained for the L4 treatment. Except for the GY of L3 and L4 treatments in 2019–2020, there was no significant difference, and the other treatments were significantly lower than that of L4. Compared with L4, the average GY of L3, L5 and L6 decreased by 7.5%, 8.9% and 21.7%, respectively.

Table 3

Effects of different irrigation treatments on grain yield, yield components and water use efficiency in winter wheat. Different letters indicate significant difference treatments at P < 0.05 level. Y, year; I, irrigation time. *, **, and *** indicate significant effects at P < 0.05, P < 0.01 and P < 0.001, respectively; ns indicates no significant effect. Values are means ± standard error (n = 3). ANOVA, analysis of variance; WUE, water use efficiency.
Year	Treatment	Spike Number (×10⁴ ha^− 1)	Grain numbers per spike	1000-grain Weight(g)	Grain Yield (kg ha^− 1)	WUE (kg ha^− 1 mm^− 1)
2018–2019	L3	700.7 b	34.3 a	30.5 d	6692.7 b	16.5 c
	L4	740.3 a	33.1 a	32.7 c	7644.2 a	19.5 a
	L5	676.5 b	31.5 ab	34.1 b	6601.6 b	17.3 b
	L6	594.0 c	28.8 b	37.9 a	5884.0 c	16.1 c
2019–2020	L3	779.9 ab	29.3 a	35.5 d	7436.9 ab	16.6 b
	L4	818.4 a	27.5 a	37.5 c	7631.3 a	17.6 a
	L5	726.0 bc	26.3 ab	41.1 b	7259.3 b	17.0 b
	L6	676.5 c	23.3 b	43.6 a	6012.9 c	14.4 c
2020–2021	L3	674.3 ab	35.3 a	34.7 d	7626.6 b	17.6 b
	L4	699.6 a	34.4 ab	36.2 c	8233.3 a	19.5 a
	L5	632.5 bc	33.4 ab	38.3 b	7555.4 b	18.1 b
	L6	600.6 c	30.5 b	40.7 a	6518.8 c	16.5 c
ANOVA	Year (Y)	***	***	***	***	***
	Irrigation(I)	***	***	***	***	***
	Y×I	ns	ns	***	***	***

Leaf area index (LAI), dry matter accumulation and harvest index (HI)

The LAI at the anthesis stage reached its maximum value at L3, and the three-year average was 6.8. Compared with L3, the LAI decreased with the delay in irrigation (L4, L5, and L6) by 7.4%, 15.2% and 30.1%, respectively (Fig. 3). After the anthesis period, the LAI of each treatment began to decrease, but the range of decrease differed. L3 and L6 decreased significantly from 15 days after anthesis (DAA) in 2018–2019 and 2020–2021, while those from 15 DAA responded similarly in 2019–2020. The LAI of L4 and L5 decreased from DAA 15–20, but the rate of decrease was lower than those of L3 and L6. After 20 DAA, the LAI of L4 and L5 were significantly higher than those of the other treatments. This indicated that a moderate delay in irrigation could effectively prolong the LAI of grain filling in the middle and late stages.

Dry matter accumulation at the anthesis stage (DMA) decreased with the delay of irrigation time (Fig. 4), and the DMA at L3 was significantly higher than those of the other treatments. Dry matter accumulation at maturity (DMM) reached its maximum value at L4, with a three-year average of 17,925.7 kg ha^− 1, and there was no significant difference between L3 and L4. However, they were significantly higher than those of L5 and L6. Compared with L4, the DAM of L5 and L6 were 6.0% and 14.9% lower than that of L4, respectively.

There were differences in the HI values during the three-year period owing to the effects of the DMA and grain yield. However, L4 achieved the highest HI over three years with an average of 0.44 (Fig. 5), which was significantly higher than that of other treatments in 2018–2019 and 2021–2022. Compared with L4, L3, L5 and L6 were reduced by 6.0%, 4.5% and 6.5%, respectively.

Water consumption

Table 4

Effects of different irrigation time on total water consumption (ET), soil water consumption (ΔSW) and their water consumption ratios during the 2018–2021 wheat growing seasons.
Year	Treatment	ET (mm)	I (mm)	P (mm)	ΔSW (mm)	Ratio to total water consumption (%)
Year	Treatment	ET (mm)	I (mm)	P (mm)	ΔSW (mm)	Irrigation	Precipitation	Soil water
2018–2019	L3	405.4 a	90	85.9	229.5 a	22.2 c	21.2 c	56.6 a
	L4	391.6 b	90	85.9	215.7 b	22.9 b	21.9 b	55.1 b
	L5	381.8 b	90	85.9	205.9 b	23.6 b	22.5 b	53.9 b
	L6	366.0 c	90	85.9	190.1 c	24.6 a	23.5 a	51.9 c
2019–2020	L3	446.8 a	90	176.2	180.7 a	18.2 c	35.5 c	36.4 b
	L4	432.3 b	90	176.2	166.1 b	20.1 b	39.4 b	38.2 a
	L5	427.6 b	90	176.2	161.5 bc	20.8 a	40.8 b	37.4 a
	L6	417.2 c	90	176.2	139.6 c	21.1 a	41.2 a	32.6 c
2020–2021	L3	434.3 a	90	103.4	240.9 a	20.7 b	23.8 b	55.5 a
	L4	423.1a	90	103.4	229.7 a	21.3 b	24.5 b	54.3 a
	L5	416.5 ab	90	103.4	223.1 ab	21.6 ab	24.8 ab	53.8 ab
	L6	396.0 b	90	103.4	202.6 b	22.7 a	26.1 a	51.2 b
ANOVA	(Y)	***			***	***	***	***
	(I)	***			***	***	***	***
	Y×I	**			***	**	***	*

Before the first irrigation in spring during the three growing seasons, the soil moisture in L4, L5, and L6 all reached the level of mild stress (Fig. 6). The duration of drought exposure increased with the delay of irrigation time, showing an average of 5, 13, and 18 days in L4, L5, and L6, respectively. On the anthesis stage, the soil moisture in L3 reached the moderate drought stress level in 2021–2022, while other treatments reached the mild drought stress level. The duration of post-anthesis drought stress gradually decreased with the delay in irrigation time, and there were differences in the influence of rainfall in different years. From the 3-leaf age irrigation to maturity, the plants in L4 were exposed to drought stress for the shortest duration (37 d on average) during the three-year period, while L3, L5, and L6 were 40 d, 42 d, and 43 d, respectively.

The proportion of irrigation water in the total water consumption was 20.3%, 20.1% and 21.6% on average during three wheat growing seasons in 2019, 2020, and 2021, respectively. Precipitation accounted for 22.3%, 39.2% and 24.8% of the total water consumption during these years, respectively. The proportion of soil water consumption to total water consumption was 54.4%, 36.2% and 53.7% on average during these years, respectively (Table 4). This shows that precipitation ratio only slightly varied under different annual types, while precipitation as a percentage of ET and soil water consumption as a percentage of ET varied substantially under different annual types, which was caused by different amounts of rainfall during the wheat season.

Year (Y), irrigation (I) treatment and their interaction significantly affected the total water consumption and stage water consumption. With the delay in the time of irrigation, the water consumption and soil water consumption gradually decreased. Compared with L3, delaying the irrigation time (L4, L5, and L6) reduced the consumption of water by 13.2 mm, 20.2 mm and 35.8 mm for L4, L5 and L6, respectively (Table 4). In 2018–2020, there was no significant difference in the consumption of total water between L4 and L5, but they were significantly lower than L3 but higher than L6. In 2020–2021, the difference in total water consumption between L3, L4 and L5 was not significant, but they were significantly higher than that of L6. The total soil water consumption in the three growth seasons was consistent with the trend of rainfall, which is expressed as the total water consumption between 2019–2020, which was the highest, followed by 2020–2021 and 2018–2019. This was owing to higher increases in rainfall, soil consumption and evapotranspiration.

Table 5

Water consumption characteristics in different wheat growth stages. CA, water consumption amount; CD, daily water consumption; CP, water consumption percentage; I, irrigation; Y, year.
Year	Treatment	Sowing to jointing			Jointing to anthesis			Anthesis to maturity
Year	Treatment	CA (mm)	CD (mm d^− 1)	CP (%)	CA (mm)	CD (mm d^− 1)	CP (%)	CA (mm)	CD (mm d^− 1)	CP (%)
2018–2019	L3	175.4 a	1.0 a	43.3 a	115.3 a	4.0 a	28.7 ab	114.7 b	3.5 b	28.7 c
	L4	145.4 b	0.8 b	37.0 b	119.3 a	4.1 a	30.7 ab	126.9 a	3.4 b	32.3 b
	L5	145.4 b	0.8 b	38.0 b	112.3 a	3.9 a	29.3 a	124.1 a	3.4 b	32.7 b
	L6	145.4 b	0.8 b	39.7 b	90.3 b	3.2 b	24.7 b	130.3 a	3.7 a	35.7 a
2019–2020	L3	173 a	1.0 a	38.7 a	115.0 a	4.0 a	25.7 bc	158.8 b	4.5 b	35.7 c
	L4	140.8 b	0.8 b	32.7 b	125.9 a	4.3 a	29.3 a	165.6 ab	4.4 b	38.3 bc
	L5	140.8 b	0.8 b	33.0 b	119.5 a	4.1 a	28.0 ab	167.3 ab	4.4 b	39.3 ab
	L6	140.8 b	0.8 b	34.0 b	99.5 b	3.5 b	24.0 c	176.9 a	4.9 a	42.3 a
2020–2021	L3	189.4 a	1.0 a	43.7 a	123.6 ab	4.3 ab	28.7 ab	121.4 b	3.8 b	27.7 c
	L4	152.8 b	0.9 b	36.3 b	130.8 a	4.5 a	31.0 a	139.5 a	3.9 b	33.0 b
	L5	152.8 b	0.9 b	36.7 b	123.4 ab	4.3 ab	29.7 a	140.3 a	3.9 b	33.7 b
	L6	152.8 b	0.9 b	38.3 b	101.4 b	3.4 b	24.0 b	141.8 a	4.2 a	37 a
ANOVA	Year(Y)	***	ns	***	***	ns	ns	***	***	***
	Irrigation(I)	***	***	***	***	***	***	***	***	***
	Y×I	ns	ns	ns	*	ns	ns	**	ns	ns

Year and irrigation significantly affected the water consumption (CA), water consumption intensity (CD) and water consumption modulus coefficient (CP) in growth stages, and the interaction of year and irrigation significantly affected CA (Table 5). The CA, CD and CP from the sowing to jointing stages showed that the irrigated treatment (L3) was significantly higher than those of the non-irrigated treatments (L4, L5, and L6). CA and CD were significantly higher in L3, L4 and L5 than in L6 from the jointing to anthesis stages, while the CP from the jointing stage to anthesis stage was L4 > L5 > L3 > L6. The CA from anthesis to maturity in L3 was significantly lower than those of L4, L5, and L6. The results showed that delayed irrigation enables winter wheat to use more water during the grain-filling period.

Dynamics of the wheat population

The tiller numbers of wheat in different treatments showed a unimodal change, reaching a peak at the standing stage, and then decreasing with the growth process (Fig. 7) at the jointing stage. The total tiller number in the irrigation treatment (L3) was significantly higher than those in the non-irrigated treatments (L4, L5, and L6). From jointing to anthesis, the tiller death rate of L3, L4 and L5 increased with the delay in irrigation time. The average number of tillers at booting decreased by 6.4%, 13.6%, and 20.0%, respectively, compared with L3, and decreased by 2.7%, 9.8% and 16.8% at anthesis, respectively. L3 decreased rapidly compared with L4, L5 and L6 after anthesis, resulting in a lower spike number than L4, and the difference reached a significant level in 2018–2019 (Fig. 7a). These results indicated that delayed irrigation reduced the number of tillers before anthesis, but irrigating too early (L3) will cause a rapid decline in tiller numbers after anthesis.

The senescence process and photosynthetic characteristics

The photosynthetic rate (Pn) and chlorophyll content (Chl) showed a consistent trend of first increasing and then decreasing after anthesis, but the peak time of different treatments of limited irrigation differed (Fig. 8, 9). L3 and L6 reached their peaks at 5–10 DAA, while L4 and L5 reached their peaks at 10–15 DAA. Both Pn and Chl obtained their maximum values at L4, which were 27.3 and 4.5, respectively. The Pn peaks of L3, L5, and L6 were 5.8%, 3.2%, and 4.4% lower than those of L4, respectively. In addition, the Chl peaks of L3, L5, and L6 were 6.8%, 2.7%, and 3.0% lower than those of L4. This indicated that moderately delayed irrigation in L4 increased the maximum photosynthetic rate and chlorophyll content. After the peak value, the Pn and Chl trends were L4 > L5 > L6 > L3, and the Pn and Chl of L3 and L6 decreased rapidly compared with those of L4 and L5.

Compared to other treatments, L4 significantly increased the activity of the SOD in flag leaves after anthesis (Fig. 10a, b, c). The accumulation of MDA in L3 and L6 at the anthesis stage was significantly higher than that in L4, and the difference gradually increased with the progress of the filling period (Fig. 10d, e, f). The accumulation of MDA in L5 was significantly higher than that of L4 at 10 to 20 DAA. Overall, L4 enhanced the activity of leaf antioxidant enzyme activity and inhibited the excessive accumulation of MDA, which ultimately delayed leaf senescence.

Correlation analysis of yield factors, water consumption characteristics and physiological indicators

A significant positive correlation was observed between GY, SN and LAI, whereas LAI significantly positively correlated with DMM and CA-JA (Fig. 11). CA-JA also significantly positively correlated with GY. GN significantly positively correlated with DMM and MDA. There was a significant positive correlation between Pn and Chl. TGW significantly negatively correlated with DMM, GN and DMA. MDA significantly negatively correlated with Pn, Chl and SOD. No significant correlation was observed between HI, WUE, and the other indicators.

Limited irrigation and watering during the critical growth stage of crops is an advanced irrigation management method and optimization tool. The amount of this irrigation method cannot fully meet the needs of crops, but it is necessary to accurately control the time of irrigation^43,44. Previous studies have shown that the limited irrigation technique can reduce water use and improve WUE^45,46. Currently, water-saving cultivation is a promising technology in the region. In this study, under the premise of sufficient soil moisture before sowing, winter wheat was irrigated once with different spring leaf ages as irrigation periods. The three-year experimental results showed that the yield and WUE varied between 6,012.9 kg ha^− 1 and 8,233.3 kg ha^− 1 and 14.4 and 19.6, respectively, under limited water irrigation (Table 3). Both achieved higher grain yield and WUE when the 4-leaf age was irrigated. This indicated that under the condition of single irrigation in spring in the North China Plain, irrigation at the 4-leaf age of wheat in spring was the optimal time for water use efficiency and grain yield.

Effects of irrigation on water use efficiency

Irrigation time is an important factor for a single irrigation. The three-year results showed that delayed irrigation reduced the water consumption of winter wheat by up to 19.7% compared with L3, while the WUE reached its maximum in L4. L3 was subjected to drought stress for the longest time after anthesis, which resulted in the early senescence of flag leaves and a reduction in the 1,000-grain weight. L5 and L6 were subjected to mild drought stress for a long time before irrigation. This stage is also the key stage of panicle development and stem-tiller differentiation, which results in different degrees of reduction in panicle number and grain number per panicle. From the beginning of irrigation to the maturity stage, the drought stress time of L4 was the shortest compared with the other treatments, which ensured a better soil environment before and after the anthesis of wheat (Fig. 6). Simultaneously, L4 showed the highest CA, CD and CP during the jointing-anthesis stage, which also indicated that the utilization of water at this stage was ultimately beneficial to the formation of yield (Table 5). CA, CD and CP from the anthesis stage to maturity stage were the highest in L6, but L6 did not produce higher yields, which could be owing to a large amount of ineffective water evaporation caused by the smaller population.

Effects of grain yield and yield components

The key growth stage of winter wheat is the jointing and grain filling stages, where water shortages can lead to severe decreases in grain yields³⁷. However other studies have shown that limited water irrigation in the specific growing period of winter wheat will not lead to a decrease in yield and can even maintain or even increase yields⁴⁷.There is a mutually beneficial relationship between WUE and yield, and in areas < 200 mm of precipitation during the growing season and loamy or sandy soil, deficit irrigation can effectively improve the WUE⁴⁸. Guo et al³⁷ reported that irrigation one time increased the WUE and soil water consumption, and the WUE decreased with the increase in irrigation. The yield of winter wheat is closely related to aboveground biomass production and HI⁴⁷. One-time irrigation at jointing increased the ratio of contribution of dry matter after anthesis to grain and, thus, improved the HI and GY⁴⁹. Some studies have shown that irrigation can enhance the LAI, delay leaf senescence, and increase the duration of leaf area⁵⁰. Limited irrigation between the jointing and anthesis stages significantly increased the wheat yield and WUE by increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves⁵¹. In this study, delaying irrigation up to the 4-leaf age (i.e., L4) did not significantly reduce the number of grains but slightly increased the spike numbers. However, it significantly increased the 1,000-grain weight (Table 3), which was the reason for the higher yield at L4. Although higher grain weights were obtained when the plants were irrigated at the 5- or 6-leaf ages (i.e., treatments L5 and L6), this treatment eventually resulted in significantly lower yields owing to a significant reduction in the numbers of ears and grains per ear (Table 3). This effect occurred because the irrigation time was delayed, and the decrease in grain number was conducive to the grain filling of wheat. This shows that early or late irrigation will not help to obtain a higher yield, and there is no significant difference between L3 and L4 in 2019–2020, which could be owing to more precipitation in April and May (Fig. 1b). We found that the highest LAI and DMA were obtained at the anthesis stage under 3-leaf-age irrigation. This could be related to the fact that the irrigation at the 3-leaf age in spring resulted in the vigorous growth of wheat populations pre-anthesis. However, a reduction in post-anthesis LAI and leaf senescence were delayed by postponing irrigation to the 4-leaf age, which promoted the DMA at the grain-filling stage and increased the contribution of post-anthesis dry matter to the grain, which, in turn, increased yield. This is consistent with previous studies that found that moderately low growth in the LAI of wheat does not result in low yields. Moderate water deficits in March can save water, and therefore, the aim should be to avoid irrigation in March^49,52.

Effects of irrigation on Chl, Pn and LAI

Previous research has shown that the physiology and growth of wheat are affected by soil water content⁴⁴. Muhammad⁵³ found that winter wheat is highly resistant to mild and moderate abiotic stress before jointing, and properly delaying irrigation can delay leaf senescence, increase the Pn, increase the activity of SOD, and reduce the concentration of MDA.

In this study, the changes of SOD and MDA differed under different irrigation treatments in the three wheat growing seasons (Fig. 10). After 10 DAA, the SOD in L4 began to maintain high activity, which negatively correlated with the content of MDA. At 20 DAA, the activity of SOD was significantly higher than that of the other irrigation treatments, while the content of MDA was significantly lower than that of the other irrigation treatments. The results showed that under the same amount of irrigation, different irrigation periods had varying effects on the post-anthesis antioxidant capacity of winter wheat. The activity of SOD can be effectively activated in the L4 treatment, which inhibited the accumulation of MDA. This demonstrated the importance of SOD as an antioxidant. This was consistent with the trend of variation of Pn and Chl in the flag leaves. This is similar to the results of previous studies⁵⁴.

Leaf age irrigation is an advanced irrigation management method, which can be used to achieve higher yield and WUE by one-time irrigation at the critical stage when the crops are most sensitive to water under limited water conditions. This study evaluated the effects of different irrigation time on the GY, WUE and physiological characteristics of the flag leaves of winter wheat based on a three-year field experiment. The results showed that compared to other treatments, 4-leaf-age irrigation increased the water consumption during jointing to anthesis, resulting in a higher grain number. 4-leaf-age irrigation shorted the accumulative duration of drought stress, delayed leaf senescence, increase the activity of SOD, reduced the concentration of MDA, and increased LAI, Pn and dry matter accumulation. While 5-leaf age irrigation and 6-leaf age irrigation exacerbated drought stress before irrigation, and significantly reduced LAI and antioxidant properties, resulting in premature senescence of flag leaves and lower grain number. Therefore, one-time irrigation at the 4-leaf stage in the spring balanced the drought stress before and after irrigation, was the best irrigation scheme to save water and generate high yields of winter wheat in the north China Plain.

Funding

This study was funded by Key R&D projects in Hebei Province (Grant No.31327001D), the Foundation of State Key Laboratory of North China Crop Improvement and Regulation (NCCIR2021ZZ-24), Modern agricultural industrial technology system of Hebei Province (HBCT2018010205), Startup Fund of Hebei Agricultural University (YJ2020050, NCCIR2020RC-10).

Declarations

Conflict of interest the authors declare that they have no competing financial interests or personal relationships.

We comply with the IUCN Policy Statement on Research Involving Species at Risk of Extinction and the Convention on the Trade in Endangered Species of Wild Fauna and Flora.

Data Availability Statement

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

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No competing interests reported.

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Single irrigation at the four-leaf stage in the spring optimizes winter wheat water consumption characteristics and water use efficiency

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Abstract

Figures

Introduction

Materials And Methods

Experimental site description

Experimental design

Sampling and measurements

Soil water

Dynamics of winter population

Leaf area index (LAI) and Dry matter accumulation (DM)

Leaf chlorophyll content and photosynthetic rate

Antioxidant enzyme activities and the content of malondialdehyde

Grain yield and yield components

Statistical analysis

Results

Grain yield, yield components and WUE

Leaf area index (LAI), dry matter accumulation and harvest index (HI)

Water consumption

Dynamics of the wheat population

The senescence process and photosynthetic characteristics

Correlation analysis of yield factors, water consumption characteristics and physiological indicators

Discussion

Effects of irrigation on water use efficiency

Effects of grain yield and yield components

Effects of irrigation on Chl, Pn and LAI

Conclusions

Declarations

References

Additional Declarations

Status:

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