Application of Organic Fertilizers Optimizes Water Consumption Characteristics and Improves Seed Yield of Oilseed Flax in Semi-Arid Areas of the Loess Plateau

Abstract

Organic fertilizers are an important source of nutrients for improving farmland fertility. To explore high-yield, efficient and green production technology for oilseed flax in dryland agricultural areas, a field split plot experiment was conducted in the semi-arid area of the Loess Plateau in northwest China from April to August in 2020 and 2021. The study compared and analyzed the effects of different nutrient sources and their application rates on water consumption characteristics, grain yield and water use efficiency of oilseed flax. The main plots were fertilizer types (sheep manure, chicken manure and chemical fertilizer), while the subplots were fertilizer application rates (sheep manure: S1-12,500 kg·hm⁻² and S2-25,000 kg·hm⁻²; chicken manure: C1-5800 kg·hm⁻² and C2-11,600 kg·hm⁻²; chemical fertilizer: F1-N 112.5 kg·hm⁻², P 75 kg·hm⁻², K 67.5 kg·hm⁻² and F2-N 225 kg·hm⁻², P₂O₅ 150 kg·hm⁻², K₂O 135 kg·hm⁻²). The results showed that compared with chemical fertilizers, organic fertilizers significantly increased the soil water storage capacity of the 0–160 cm soil layer during the whole growth period of oilseed flax and significantly reduced water consumption. During two growing seasons, the application of 25,000 kg·hm⁻² sheep manure significantly reduced water consumption during the seedling-bud period and green fruit period-maturity period of oilseed flax by 16.13% and 23.19% compared with CK, respectively. Thousand-grain weight, yield and water use efficiency were significantly increased by 14.70%, 48.32% and 61.29%, respectively. These results indicate that the application of 25,000 kg·hm⁻² sheep manure can significantly increase soil water storage capacity of the 0–160 cm soil layer, reduce water consumption during the whole growth period of oilseed flax and thus improve grain yield and water use efficiency of oilseed flax. It is a suitable fertilization technology for the high-yield, efficient and green production of oilseed flax in the semi-arid areas of northwest Loess Plateau.

1. Introduction

The Loess Plateau has a large area of dry farmland and is one of the main dry farming areas in China. The region is characterized by severe drought, low forest coverage, sparse vegetation and poor soil. Long-term soil erosion has led to desertification and land degradation, making the ecological environment extremely fragile and unfavorable for sustainable agricultural production in the region [1]. Improving crop productivity under limited water resources has been a long-standing challenge in this area. Oilseed flax (Linum usitatissimum L.) is one of the main oil crops in this region due to its characteristics of drought resistance, cold resistance, short growth period and wide adaptability. However, water is the main limiting factor for increasing oilseed flax yield [2]. How to use water efficiently and ensure oilseed flax production is an urgent problem that needs to be solved.

In the process of crop production, fertilizers have made important contributions to promoting crop growth and increasing yield [3] but the excessive use of fertilizers has caused ecological environment pollution and soil fertility decline [4]. Therefore, exploring fertilization measures that can improve soil fertility, increase yield and efficiency, and are environmentally friendly is of great significance for sustainable agricultural production in farmland. Organic fertilizers can increase the porosity and soil permeability of the plow layer, promote soil suppression and moisture retention [5], improve the water storage and water retention performance of the soil, and to a certain extent coordinate the impact between crop water demand and soil water supply, thereby improving fertilizer utilization efficiency and water use efficiency [6]. Organic fertilizers can not only meet the nutrient requirements of crops but also coordinate the impact between the rice root system and soil water supply, thereby improving crop yield and water use efficiency [7]. Studies have shown that no-tillage and organic fertilizers play an important role in improving the water storage efficiency of dryland winter wheat during its growth period [8]. A single application of organic fertilizer can reduce the pre-flowering water consumption of crops, increase the post-flowering water consumption, and play a regulatory role of “fertilizer-water regulation” during critical periods of crop growth and development [9,10]. The combination of organic-inorganic fertilizers can improve soil fertility, improve soil structure, enhance soil water-holding capacity, and significantly improve crop yield and water-fertilizer utilization efficiency [6]. Some studies have also shown that reducing chemical fertilizer application while applying organic fertilizer can improve wheat quality and increase soil organic matter content in the plow layer [11]. However, previous studies have mostly focused on aspects such as tillage methods [12], no-tillage combined with inorganic fertilizers [13], and the impact of organic fertilizers replacing chemical fertilizers [14] on crop yield and quality, while there are few reports on the study of organic fertilizers on crop stage water consumption characteristics in dryland agricultural areas. Therefore, this study conducted field experiments in northwest semi-arid rain-fed agricultural areas in 2020 and 2021 to (i) clarify the effects of no fertilizer application, chicken manure, sheep manure, and single chemical fertilizer application on oilseed flax stage water consumption; (ii) explore the effects of organic fertilizers on oilseed flax yield and its constituent factors as well as water use efficiency; (iii) propose a suitable fertilization plan for green oilseed flax production in northwest dryland agricultural areas. In order to provide theoretical basis and technical support for high-efficiency green sustainable production of oilseed flax in dryland agricultural areas.

2. Materials and Methods

2.1. Study site Description

This study was conducted from April 2020 to August 2021 at the Oil Crops Institute of Gansu Academy of Agricultural Sciences (N 35°48′, E 104°49′) experimental base in Dingxi City, Gansu Province, China (Figure 1). The experimental area belongs to a hilly and gully semi-arid area of the Loess Plateau, with an average altitude of 2050 m, an average annual sunshine duration of 2453 h, a frost-free period of 140 d, average annual precipitation of 390 mm, annual evaporation of up to 1500 mm, an average annual temperature of 6.3 °C, an extreme maximum temperature of 34.3 °C, and an extreme minimum temperature of −27.1 °C. The experimental site is terraced and the soil is loess soil. The total nitrogen content of the plow layer soil is 0.81 g·kg⁻¹, organic matter content is 10.12 g·kg⁻¹, total phosphorus is 0.69 g·kg⁻¹, alkali-hydrolyzed nitrogen is 48.91 mg·kg⁻¹, available phosphorus is 27.43 mg·kg⁻¹, available potassium is 108.30 mg·kg⁻¹, and pH is 8.14.

The total precipitation from sowing to harvest in 2020 and 2021 was 294.3 mm and 182.7 mm, respectively. The effective precipitation days during the growing season accounted for 57.58% (2020) and 52.77% (2021) of the growing season. The average maximum temperature during the planting year in 2020 and 2021 was 28.9 °C and 28.1 °C, respectively, and the average minimum temperature during the planting year in 2020 and 2021 was 2.8 °C and 2 °C, respectively. Compared with the long-term average value of crop growing season precipitation (453.3 mm) from 1961 to 2021 for nearly 61 years, the oilseed flax growing season precipitation in 2020 (511.1 mm) and 2021 (339.8 mm) were abundant and drought years, respectively (Figure 1).

2.2. Experimental Design

This experiment adopts a two-factor split-plot randomized block experimental design. The type of fertilizer is the main plot A factor, with three levels of mature chicken manure (C), mature sheep manure (S), and chemical fertilizer (F). The main plot was 7.5 m long and 2 m wide. The amount of fertilizer is the subplot B factor, with two levels of 112.5 kg·hm⁻² (N), 75 kg·hm⁻² (P₂O₅), 67.5 kg·hm⁻² (K₂O) and 225 kg·hm⁻² (N), 150 kg·hm⁻² (P₂O₅), 135 kg·hm⁻² (K₂O). The subplot was 2.5 m long and 2 m wide. All treatments followed nutrient fertilization with N, P, K, etc., and excess nutrients were balanced with calcium superphosphate and potassium sulfate. The specific fertilizer application rates are shown in

Table 1. Application amount of organic fertilizer.

Organic Fertilizer	Treatment	Application Amount of Organic Fertilizer (kg·hm−2)	N (kg·hm−2)	P (kg·hm−2)	K (kg·hm−2)
Chicken manure	C1	5800 a	0	115.4	49.3
	C2	11,600	0	230.8	98.6
Sheep manure	S1	12,500 b	0	240	56.3
	S2	25,000	0	480	112.5
Chemical fertilizer	F1	0	112.5	75	67.5
	F2	0	225	150	135
No fertilizer	CK	0	0	0	0

^a Conversion based on N content in chicken manure (N: 1.94%, P₂O₅: 1.54%, K₂O: 0.85%), consistent with the N content of the fertilizer treatment; ^b Conversion based on the N content of sheep manure (N: 0.9%, P₂O₅: 0.5%, K₂O: 0.45%), consistent with the N content of the fertilizer treatment.

. CK was used as the control group without fertilization, and there were seven treatments in total, each repeated three times. The material used was the Longya No.10 oilseed flax variety, with a sowing rate of 7.5 million seeds·hm⁻², sown in rows at a depth of 3 cm and a row spacing of 20 cm.

The fertilizers used were mature chicken manure (N: 1.94%, P₂O₅: 1.54%, K₂O: 0.85%), mature sheep manure (N: 0.9%, P₂O₅: 0.5%, K₂O: 0.45%), urea (containing N 46%), calcium superphosphate (containing P₂O₅ 16%), and potassium sulfate (containing K₂O 51%). Organic and chemical fertilizers were all turned and buried 1 week before sowing, at a depth of 20 cm of soil. The experiment was sown on 4 April 2020 and harvested on August 18, with a growth period of 136 days. It was sown again on 8 April 2021 and harvested on 11 August, with a growth period of 125 days. Other management was the same as that of general fields.

2.3. Measurement Items and Methods

Soil water content was measured at different growth stages of oilseed flax: seedling stage, bud stage, green fruit stage and mature stage. Soil samples were collected from 0 to 160 cm soil layers in the oilseed flax planting belt using a soil drill with a diameter of 5 cm. Samples were taken at 20 cm intervals for a total of eight layers. The fresh weight, dry weight and aluminum box weight of the soil were measured (105 °C oven method, GWC, %). Soil water content (SWC) was calculated [15].

$$\mathrm{SWC}=\frac{{\mathrm{M}}_1-{\mathrm{M}}_2}{{\mathrm{M}}_2}\times 100\%$$

(1)

In the formula, M₁ represents the fresh weight of the soil (g) and M₂ represents the dry weight of the soil (g). Based on the soil water content, the soil water storage capacity, water consumption and water use efficiency were calculated.

Soil water storage is calculated by the formula

$${\mathrm{S}}_{\mathrm{w}}=\mathrm{d}\times \mathrm{r}\times \mathrm{w}/10$$

(2)

In the formula, S_w represents the soil water storage capacity (mm), d represents the thickness of the soil layer (cm), r represents the bulk density of the soil (g/cm³), and w represents the soil water content (%).

Water consumption formula (Evapotranspiration, ET) [16]

$${\mathrm{ET}}_{\mathrm{i}}={\mathrm{SW}}_{\mathrm{i}}-{\mathrm{SW}}_{\mathrm{i}+1}+{\mathrm{P}}_{\mathrm{i}}$$

(3)

In the formula, ET_i represents the water consumption (mm), ${\mathrm{SW}}_{\mathrm{i}}$ represents the soil water storage capacity at the beginning of a certain growth period (mm), ${\mathrm{SW}}_{\mathrm{i}+1}$ represents the soil water storage capacity at the end of that growth period (mm), and ${\mathrm{P}}_{\mathrm{i}}$ represents the precipitation during that growth period (mm).

The water consumption modulus (water consumption percentage, WCP) is calculated by the formula

$$\mathrm{WCP}={\mathrm{ET}}_{\mathrm{i}}/\mathrm{ET}\times 100\%$$

(4)

where ET_i is the water consumption at a certain stage and ET is the total water consumption during the reproductive period.

Yield measurement: At the mature stage of oilseed flax, 30 plants were randomly sampled from each plot and brought back to the laboratory for seed extraction. The number of effective fruits per plant, the number of grains per fruit, the thousand-grain weight and the yield per plant were measured. At harvest time, the plots were harvested individually and the actual yield per unit area was measured.

The water use efficiency is calculated by the formula

$$\mathrm{WUE}=\mathrm{Y}/\mathrm{ET}$$

(5)

In the formula, WUE represents the water use efficiency of the crop (kg ha⁻¹·mm⁻¹), Y represents the seed yield of the crop (kg/ha⁻¹), and ET represents the water consumption during the growth period (mm).

2.4. Statistical Analysis

Microsoft Office Excel 2021 (Microsoft Corporation, Redmond, WA, USA) was used for data organization, Adobe Illustrator CC 2021 (Adobe, San Jose, CA, USA) and R language (University of Auckland, Auckland, New Zealand) were used for drawing, Golden Software Voxler 4 was used for 3D visualization, and Golden Software Surfer 21 (Golden Software, Golden, CO, USA) was used for 2D visualization and geological statistical analysis. SPSS 22.0 statistical software (SPSS, Inst., Cary, NC, USA) was used for data analysis and Significant differences between means in all ANOVAs were identified using Duncan at p ≤ 0.05.

3. Results

3.1. Spatiotemporal Changes in Soil Water Content in the 0–160 cm Soil Layer of Oilseed Flax under Organic Fertilizer Treatment

The 3D spatial distribution of soil water content in oilseed flax, formed by the grid interpolation method (Figure 2), shows that during the two growing seasons of oilseed flax, sheep manure (S) significantly increased the soil water content in the 0–160 cm soil layer. This was 3.77% and 3.25% higher than that of chicken manure (C) and chemical fertilizer (F), respectively. In terms of soil layers, the soil water content in the 0–120 cm soil layer of oilseed flax generally showed a trend of first decreasing and then increasing with the depth of the soil layer, while the 120–160 cm soil layer showed a decreasing trend. Comparative analysis of different growth stages of oilseed flax found that the vertical change in soil water content in the 0–160 cm soil layer was greatly influenced by the fertilization level. Looking at different fertilizer treatments, the soil moisture content at the bud stage was 5800 kg·hm⁻² for chicken manure (C1), which was significantly reduced by 1.70% and 2.82% compared to the base application of sheep manure 12,500 kg·hm⁻² (S1) and the application of chemical fertilizer 112.5 kg·hm⁻² (F1), respectively (2020); the soil moisture content at the green fruit stage was significantly reduced by 10.25% and 4.94%, 5.84% for S1 compared to F1 and C1, respectively (2021), and 225 kg·hm⁻² (F2) was significantly reduced by 3.69% and 4.81% compared to the chicken manure application of 11,600 kg·hm⁻² (C2) and the base application of sheep manure 25,000 kg·hm⁻² (S2), respectively; the soil moisture content at the mature stage was significantly reduced by 7.07% and 17.9%, 24.6% for C2 compared to F2 and S2, respectively (2021), and C1 was significantly reduced by 18.22% and 24.6% compared to F1 and S1, respectively. Under different fertilization levels, the soil water content during the green fruit stage and the mature stage was significantly higher for sheep manure than for no fertilization (CK), with a base application of 12,500 kg·hm⁻² (S1) and 25,000 kg·hm⁻² (S2) being significantly higher than CK by 3.41–5.26% and 7.54–9.11%, respectively (2021); base application of 5800 kg·hm⁻² chicken manure (C1) significantly increased the soil water content during the bud stage and green fruit stage of oilseed flax, significantly reducing it by 2.7% and 7.16% compared to 11,600 kg·hm⁻² chicken manure (C2), respectively; application of chemical fertilizer significantly reduced the soil water content during the green fruit stage and mature stage, with 112.5 kg·hm⁻² (F1) and 225 kg·hm⁻² (F2) being significantly lower than CK by 8.77% and 12.81%, respectively (2020). In summary, the base application of 25,000 kg·hm⁻² sheep manure significantly increased the soil water content in the 0–160 cm soil layer, which is conducive to alleviating the harm of drought to oilseed flax.

3.2. Spatiotemporal Changes in Soil Water Storage Capacity during the Entire Growth Period of Oilseed Flax under Different Organic Fertilizer Treatments

During the two growing seasons, sheep manure (S) significantly increased the soil water storage capacity in the 0–160 cm soil layer of oilseed flax throughout the growth period, increasing by 2.21% and 2.80% compared to chicken manure © and chemical fertilizer (F) treatments, respectively (Figure 3). The distribution of soil water storage capacity during different growth stages of oilseed flax under sheep manure treatment was relatively uniform in the horizontal position. In terms of soil layer distribution, the soil water storage capacity in the 0–60 cm and 120–160 cm soil layers was lower than that in the 60–120 cm soil layer, and this distribution trend weakened during the green fruit stage (Gs). Comparative analysis of different growth stages of oilseed flax found that there was a large difference in soil water storage capacity in the 0–160 cm soil layer under different fertilization levels. Base application of 5800 kg·hm⁻² chicken manure (C1) significantly increased the soil water storage capacity during the seedling and mature stages of oilseed flax, significantly increasing by 5.09% (2021) and 13.18% (p < 0.05), respectively, compared to the base application of 225 kg·hm⁻² chemical fertilizer (F2); the base application of 11,600 kg·hm⁻² chicken manure (C2) significantly increased the soil water storage capacity during the green fruit stage, significantly increasing it by 7.16% (p < 0.05) compared to C1 treatment. Base application of 12,500 kg·hm⁻² (S1), 25,000 kg·hm⁻² (S2) sheep manure and 225 kg·hm⁻² (F2) chemical fertilizer significantly increased the soil water storage capacity during the green fruit stage and mature stage, respectively, significantly increasing by 3.41–6.21%, 7.54–21.08%, and 3.21–6.00% compared to C1 treatment, and significantly increasing by 5.26–8.11%, 9.11–32.60%, and 7.40–20.92% compared to no fertilization (CK), respectively. Looking at different fertilizer treatments, the soil water storage capacity at the bud stage was significantly reduced by 2.82% for C1 compared to S1; the soil water storage capacity at the green fruit stage was significantly reduced by 5.84% and 4.94% for C1 and F1 compared to S1, respectively; the soil water storage capacity at the mature stage was significantly reduced by 18.22% and 17.41% for C1 compared to F1 and S1, respectively, and C2 was significantly reduced by 23.39% and 24.59%, 12.90% compared to F2 and S2, respectively (2020). In summary, the application of organic fertilizer can significantly increase the soil water storage capacity in the 0–160 cm soil layer of oilseed flax throughout the growth period, and the application of 25,000 kg·hm⁻² sheep manure can significantly increase the soil water storage capacity during key growth stages of oilseed flax, which is conducive to its growth and development.

3.3. The Effect of Different Organic Fertilizer Treatments on Water Consumption Characteristics during Different Growth and Development Stages of Oilseed Flax

Water consumption (ET) during different growth stages of oilseed flax mainly relies on natural precipitation (

Table 2. Precipitation and soil water storage consumption at the different growth stages.

Year	Treatments	Seedling-Budding				Budding-Green Fruit				Green Fruit-Mature
		P		ΔW [17]		P		ΔW		P		ΔW
		mm	%	mm	%	mm	%	mm	%	mm	%	mm	%
2020	C1	107.2	100	−48.63 a	0	110	41.53	154.87 b	58.47	77.1	100	−48.64 b	0
	C2			−70.86 a			37.83	180.74 a	62.17			−5.90 a
	F1			−70.84 a			38.68	174.36 ab	61.32			−49.84 b
	F2			−64.41 a			37.55	182.97 a	62.45			−34.96 ab
	S1			−66.96 a			42.34	149.79 b	57.66			−20.84 ab
	S2			−68.67 a			39.20	170.62 ab	60.80			−41.96 b
	CK			−54.42 a			42.35	149.74 b	57.65			−7.27 a
2021	C1	63.9	33.61	126.24 a	66.39	109.3	100	−14.71 ab	0.00	9.5	8.79	98.6 b	91.21
	C2		39.26	98.88 bcd	60.74			−4.22 ab			6.76	131.05 a	93.24
	F1		35.76	114.80 abc	64.24			−21.70 ab			13.24	62.25 c	86.76
	F2		36.26	112.31 abcd	63.74			−35.84 b			10.81	78.41 b	89.19
	S1		41.36	90.60 d	58.64			−7.80 a			10.77	78.69 bc	89.23
	S2		40.56	93.64 cd	59.44			−28.12 ab			10.52	80.81 bc	89.48
	CK		35.30	117.13 ab	64.70			−17.87 a			10.16	83.98 bc	89.84
Average	C1		68.79	38.81 a	31.21		43.82	70.08 a	56.18		63.42	24.98 bc	36.58
	C2		85.93	14.01 c	14.07		56.91	78.26 a	43.09		40.90	62.57 a	59.10
	F1		79.56	21.98 bc	20.44		59.36	76.33 a	40.64		87.47	6.20 d	12.53
	F2	85.55	78.13	23.95 bc	21.87	109.65	57.62	73.57 a	42.38	43.3	66.58	21.73 bcd	33.42
	S1		87.86	11.82 c	12.14		65.80	71.00 a	34.20		59.96	28.92 bc	40.04
	S2		87.26	12.49 c	12.74		57.39	71.25 a	42.61		69.03	19.43 cd	30.97
	CK		73.18	31.35 ab	26.82		64.33	65.94 a	35.67		53.03	38.35 b	46.97

C1, C2: Chicken manure gradient; F1, F2: Chemical fertilizer gradient; S1, S2: Sheep manure gradient; CK: No fertilizer. P: precipitation; ΔW: soil water storage consumption in the 0–160 cm soil layer. Different lowercase letters represent significance at the 0.05 level between different treatments in the same column.

). Compared to CK, chicken manure (C) treatment increased the contribution rate of precipitation to evapotranspiration (P/ET) in the early stage of oilseed flax growth and development but decreased the ratio of ΔW to evapotranspiration (ΔW/ET). In the middle stage, P/ET was generally reduced, but ΔW/ET was increased. On average over two years, compared to the control CK, base application of 12,500 kg·hm⁻² (S1) and 25,000 kg·hm⁻² (S2), sheep manure fertilization levels significantly increased P/ET by 20.06% and 19.24%, respectively (or decreased ΔW/ET), compared to CK during the seedling to bud stage. During the bud to green fruit stage, P/ET for S1 was significantly higher than CK by 2.28% (or decreased ΔW/ET). The gradient of chemical fertilizer from green fruit to mature stage P/ET was significantly higher for 112.5 kg·hm⁻² (F1) treatment than CK by 64.94% (or decreased ΔW/ET).

Compared to the control, organic fertilizer reduced the soil water storage consumption (ΔW) in the 0–160 cm soil layer during the early stage of oilseed flax growth and development and was generally higher than CK in the middle and later stages. Overall, base application of 5800 kg·hm⁻² chicken manure (C1) increased ΔW from the seedling to bud stage, significantly increasing by 23.80% compared to CK. Base application of 11,600 kg·hm⁻² chicken manure (C2) increased ΔW from the green fruit to the mature stage, significantly increasing by 63.16% compared to CK.

3.4. Response of Water Consumption to Organic Fertilizer during the Reproductive Period of Oilseed Flax

According to

Table 3. The total water consumption of oilseed flax in each growth period and the percentage of total water consumption under different treatments.

Treatments		Total Water Consumption (mm)	Evapotranspiration (mm)			Ratio (%)
Year			Seedling-Budding	Budding-Green Fruit	Green Fruit-Mature	Seedling-Budding	Budding-Green Fruit	Green Fruit-Mature
2020		367.00 a	43.66 b	276.16 a	47.19 b	11.86 b	75.52 a	12.61 b
2021		356.58 a	171.56 a	87.84 b	97.18 a	48.26 a	24.71 b	27.03a
T	C	382.86 a	111.96 a	183.82 a	87.08 a	28.90 a	48.71 a	22.39 a
	F	350.38 b	108.52 a	184.60 a	57.27 b	31.73 a	51.81 a	16.45 b
	S	345.96 b	99.77 a	180.77 a	67.47 b	29.11 a	51.66 a	19.62 a
F	N112.5	355.21 a	109.75 a	182.12 a	63.34 b	30.70 a	51.71 a	17.59 b
	N225	364.25 a	102.37 b	184.01 a	77.87 a	28.87 b	49.75 a	21.38 a
	C1	372.37 b	124.36 a	179.73 a	68.28 bc	32.38 a	49.86 abc	17.76 cd
	C2	393.34 a	99.56 c	187.91 a	105.88 a	25.42 c	47.55 bc	27.03 a
	F1	343.02 c	107.53 bc	185.99 a	49.50 d	31.65 a	53.91 a	14.44 d
	F2	357.75 bc	109.51 bc	183.22 a	65.03 bcd	31.81 a	49.72 abc	18.47 bc
	S1	350.25 c	97.38 c	180.65 a	72.23 bc	28.07 bc	51.34 ab	20.59 bc
	S2	341.66 c	98.04 c	180.90 a	62.72 cd	29.38 ab	51.97 ab	18.66 bc
	CK	374.14 b	116.90 ab	175.59 a	81.66 b	31.73 a	46.46 c	21.81 b
Source of variance	T	***	**	ns	***	*	*	**
	F	ns	ns	ns	**	ns	ns	*
	Y	*	***	***	***	***	***	***
	T × F	ns	*	ns	**	**	ns	**
	T × Y	ns	ns	**	**	**	*	**
	F × Y	*	ns	**	ns	ns	ns	ns
	T × F × Y	ns	ns	ns	ns	ns	ns	ns

ns, *, **, *** indicate non-significant, significant or extremely significant at p < 0.05, p < 0.01 or, p < 0.001, respectively. Means followed by different letters within a column are significantly different at p < 0.05. T: Types of organic fertilizers; F: Fertilization level; Y: Year.

, the types of organic fertilizers, year, and Year × Types of organic fertilizers have a significant effect on the soil water consumption during the oilseed flax budding period-green fruit period, green fruit period-maturity period, and the proportion of soil water consumption in the total water consumption. In 2021, the water consumption during the seedling-budding period and green fruit-maturity period increased significantly by 292.95% and 105.93%, respectively, compared to 2020, and the proportion of water consumption in the total water consumption was higher by 306.91% and 114.35%, respectively. Chicken manure (C) significantly increased total soil water consumption by 9.27% and 10.67% compared to chemical fertilizer (F) and sheep manure (S), respectively. Water consumption during the green fruit-mature stage increased significantly by 52.05% and 29.06% for C compared to F and S, respectively. The stage water consumption ratio of C and S increased significantly by 36.11% and 19.27% compared to F, respectively. During the sesame seedling-bud stage, water consumption for N112.5 was significantly higher by 7.21% and 22.94% compared to N225, and the stage water consumption ratio was significantly higher by 6.34%. During the green fruit-mature stage, water consumption for N225 was significantly higher by 22.94% compared to N112.5, and the stage water consumption ratio was significantly higher by 21.55%. Applying 12,500 kg·hm⁻² (S1) and 25,000 kg·hm⁻² (S2) of sheep manure can significantly reduce soil water consumption during the seedling-budding period, reducing it by 16.70–21.70% and 16.13–21.16%, respectively, compared to applying 5800 kg·hm⁻² (C1) of chicken manure and no fertilizer (CK). The proportion of soil water consumption in the total water consumption of S2 treatment was significantly higher than that of applying 11,600 kg·hm⁻² (C2) of chicken manure by 15.58%. During the green fruit maturity period, S2 treatment significantly reduced soil water consumption by 40.76% and 23.19% compared to C2 and CK, respectively, and applying 25,000 kg·hm⁻² (S2) of sheep manure significantly reduced total soil water consumption by 0.40–13.14% compared to other treatments. Therefore, applying sheep manure can lower soil water consumption during the main growth stages of oilseed flax, total water consumption, and the proportion of soil water consumption in total water consumption. The S2 fertilizer level can significantly regulate soil water consumption during the main growth stages of the oilseed flax seedling-budding period and green fruit-maturity period and total soil water consumption, storing more soil moisture during critical periods of oilseed flax growth.

3.5. Effect of Different Organic Fertilizer Treatments on Yield and Yield Components of Oilseed Flax

According to

Table 4. Effects of Different Treatments on the Yield and Yield Component Factors of Oilseed flax.

Main Factors and Interaction		Pod Number per Plant	Seed Number per Pod/(Grain·Fruit−1)	1000-Grain Weight/g	Yield/(kg·ha−1)	WUE (kg ha−1mm−1)
2020		22.45 a	7.97 a	8.06 a	1662.90 b	6.48 a
2021		14.63 b	8.45 a	7.03 b	2354.51 a	4.68 a
T	C	15.88 b	8.08 a	7.45 a	2098.18 a	6.11 b
	F	18.93 ab	8.31 a	7.76 a	2046.20 a	7.52 a
	S	22.31 a	8.55 a	7.76 a	2164.80 a	6.92 ab
F	N112.5	18.17 a	8.06 a	7.59 a	2060.80 a	5.71 a
	N225	19.91 a	8.57 a	7.72 a	2145.32 a	6.02 a
	C1	13.37 b	7.84 ab	7.27 bc	2067.07 a	5.65 a
	C2	18.38 ab	8.32 ab	7.63 ab	2129.30 a	5.42 a
	F1	21.32 ab	8.32 ab	7.86 ab	1975.77 a	5.52 a
	F2	16.55 ab	8.29 ab	7.65 ab	2116.62 a	6.24 a
	S1	19.80 ab	8.01 ab	7.63 ab	2139.55 a	5.96 a
	S2	24.81 a	9.09 a	7.89 a	2190.05 a	6.40 a
	CK	15.53 b	7.60 b	6.88 c	1442.56 b	3.87 b
Source of variance	T	ns	ns	**	***	***
	F	ns	ns	ns	ns	ns
	Y	***	ns	***	***	***
	T × F	ns	ns	ns	ns	ns
	T × Y	ns	ns	ns	**	*
	F × Y	ns	ns	ns	ns	ns
	T × F × Y	ns	ns	ns	ns	ns

ns, *, **, *** indicate non-significant, significant or extremely significant at p < 0.05, p < 0.01 or, p < 0.001, respectively. Means followed by different letters within a column are significantly different at p < 0.05. T: Types of organic fertilizers; F: Fertilization level; Y: Year.

, organic fertilizers significantly affect the thousand-grain weight, yield, and water use efficiency of oilseed flax in two growing seasons. Sheep manure (S) significantly increased the pod number per plant by 40.49% compared to chicken manure (C), and chemical fertilizer (F) significantly increased water use efficiency by 23.08% compared to chicken manure (C). Applying 25,000 kg·hm⁻² (S2) of sheep manure significantly increased the thousand-grain weight, yield, and water use efficiency of oilseed flax, increasing them by 14.70%, 48.32%, and 61.29%, respectively, compared to CK. This indicates that organic fertilizers can reduce the consumption of soil moisture by oilseed flax and applying 25,000 kg·hm⁻² of sheep manure is conducive to promoting high-yield and efficient production of dryland oilseed flax.

3.6. Correlation Analysis between Water Consumption Characteristics and Yield Components of Oilseed Flax under Different Organic Fertilizer Treatments

The correlation analysis of water consumption characteristics and yield components of oilseed flax under organic fertilizer treatment (Figure 4) shows that the number of grains per fruit is significantly positively correlated with the thousand-grain weight, yield, and water use efficiency. Yield is significantly positively correlated with the number of grains per fruit, thousand-grain weight, and water use efficiency. Water use efficiency is significantly positively correlated with the number of grains per fruit, thousand-grain weight, and yield. However, the number of capsules per plant is significantly negatively correlated with total water consumption. In summary, the correlation analysis shows that there are different degrees of correlation between various trait indicators, and the number of grains per fruit, yield, and water use efficiency are the main factors affecting the change in oilseed flax yield.

4. Discussion

4.1. Effect of Different Organic Fertilizers on Soil Water Storage

Previous studies have shown that the rational application of organic fertilizers is beneficial for improving soil moisture conditions and is particularly important for improving the water use of dryland crops [18]. After organic fertilizers are mixed with the plow layer soil, they can effectively block the path of soil moisture evaporation and thus increase soil moisture content [19]. During the wheat greening period and grain filling period, soil water storage under organic fertilizer treatment has increased to varying degrees [20]. This study shows that under organic fertilizer treatment, soil water storage during the oilseed flax budding period is significantly higher than that of no fertilizer and a single application of chemical fertilizer. The main reason is that organic fertilizers improve the physical and chemical properties of the soil, which is conducive to rainwater infiltration. Rainfall directly acts on the roots of crops, while also improving soil water retention, reducing soil evaporation, and thus increasing soil water storage [21]. Applying 25,000 kg·hm⁻² of sheep manure has a good soil water retention effect and increases soil water storage during various growth periods. Related studies have shown that increasing the application of organic fertilizers can increase the soil moisture content in the 0–60 cm soil layer and increase deep soil water storage [22]. This study shows that during the green fruit-maturity period of oilseed flax, applying 25,000 kg·hm⁻² of sheep manure maintains a relatively high moisture content in the 0–160 cm soil profile, thereby reducing spatial differences in soil moisture at different growth stages [23], alleviating drought stress, and increasing the stability of soil profile moisture distribution. This research result is consistent with previous research results [11,23].

4.2. Effect of Different Organic Fertilizers on Water Consumption Characteristics of Oilseed Flax Fields

Regulating the water consumption process of crops is one of the main ways to improve the water use efficiency of dryland crops and resist seasonal drought, and the application of organic fertilizers can inhibit soil moisture evaporation [24]. Studies have shown that no-tillage and organic fertilizers can reduce soil water storage during the pre-greening stage of dryland winter wheat, increase soil water consumption during the greening-ear stage, and increase total water consumption during the growth period [25]. This study shows that applying 25,000 kg·hm⁻² of sheep manure can significantly reduce soil water consumption in the 0–160 cm layer during the oilseed flax seedling-budding period and green fruit-maturity period, which is beneficial to oilseed flax growth and has a positive effect on increasing oilseed flax seed yield. The application of organic fertilizers can effectively maintain soil moisture, reduce ineffective water consumption and improve the effectiveness of water use [26]. This study shows that at different growth stages of oilseed flax, the soil moisture content in each soil layer of 0–160 cm is higher under organic fertilizer treatment than under chemical fertilizer and no fertilizer treatment. Among the two organic fertilizer treatments, the moisture content of sheep manure treatment is significantly higher than that of chicken manure treatment. The fertilizer gradient was calculated from the nitrogen content of chicken manure, sheep manure, and chemical fertilizer treatment (Table 1). The amount of sheep manure S2 applied was 1.16 times that of chicken manure. After turning over the soil to a depth of 20cm, this increased soil porosity. After mixing sheep manure treatment with the soil in the plow layer, a sheep manure barrier was formed on the surface or topsoil layer, enhancing the water retention effect of the sheep manure treatment. This is because the sheep manure treatment mixed with the plow layer soil forms a sheep manure barrier on the surface or topsoil layer, enhancing the water retention effect of sheep manure treatment [27]. At maturity, sheep manure treatment maintains a relatively high soil moisture content. This may be due to its mixing with soil and its good water conduction, storage and moisture retention ability at the soil interface [28]. There are few reports on the effect of organic fertilizers on reducing soil evaporation and water consumption. In this study, compared with no fertilizer application, organic fertilizer treatment can significantly inhibit soil evaporation. The inhibitory effect is mainly reflected in the high-temperature green fruit maturity period. The main reasons are: first, organic fertilizers mixed with plow layer soil can reduce physical barriers to water and heat exchange between soil and atmosphere, effectively avoiding the exchange of water and energy between soil and atmosphere, significantly reducing soil evaporation [29]; secondly, organic fertilizers can reduce soil moisture loss in the early growth stage of oilseed flax. Oilseed flax grows slowly and consumes less water and nutrients. With the increase in temperature, the remaining soil moisture and nutrients in the early growth stage can promote oilseed flax growth and development. Organic fertilizers also increase oilseed flax’s use of deep soil water storage, reduce soil moisture stress, regulate oilseed flax’s water consumption process, play a regulatory role in “adjusting water with fertilizer”, create a suitable soil moisture environment for oilseed flax growth, and have been proven to have an effect on reducing water consumption [30]. In this study, although there was no difference in total water consumption between years under organic fertilizer treatment, there was a significant difference in stage water consumption. Among them, sheep manure treatment in 2020 had significantly lower stage water consumption during the seedling-budding period and green fruit-maturity period than in 2021. On one hand, this is because the soil water storage before sowing oilseed flax in 2021 was significantly higher than that in 2020 (Figure 1a), which enhanced the water retention effect of sheep manure treatment and improved its utilization efficiency; on the other hand, sheep manure treatment optimized crop growth dynamics by regulating soil thermal properties. Especially in the low-temperature effect before crop growth and inhibiting effect on soil evaporation (Figure 1b), more moisture was used for the later growth of oilseed flax. Organic fertilizers reduced ineffective evaporation during oilseed flax’s vegetative growth period and enhanced effective water consumption during its reproductive growth period (Table 3). Therefore, sheep manure treatment reduced water consumption during the early (seedling-budding period) and late (green fruit-maturity period) growth stages by increasing water consumption during mid-growth (budding-green fruit period), effectively coordinating conflicts between oilseed flax’s demand for water at different growth stages. In summary, organic fertilizers can optimize the water consumption characteristics of oilseed flax in dryland agricultural areas on the Loess Plateau. Further experiments are needed to explore crop water consumption and regulation in farmland.

4.3. Effect of Different Organic Fertilizers on Yield and Yield Components

Appropriate application of organic fertilizers is one of the important factors in regulating crop growth and development. By optimizing the type and amount of organic fertilizers applied, regulating crop growth dynamics, and improving the complementary relationship between crop utilization of water resources, crop yield can be effectively increased [31]. This study shows that the yield of dryland oilseed flax in a wet year (2020) is significantly lower than that in a dry year (2021). The growth period and annual type in 2020 were both wet years, but rainfall was concentrated in the budding-green fruit period from June to July. There was relatively little effective rainfall before sowing and during the seedling stage of oilseed flax, resulting in a decrease in the number of effective fruits, a decrease in thousand-grain weight, and a decrease in yield level. The growth period and annual type in 2021 were dry years, but there was more effective rainfall during the critical growth period of oilseed flax in June and more rainfall before sowing. The number of effective fruits, thousand-grain weight, and yield of oilseed flax were all higher than those in 2020. Therefore, dryland oilseed flax is not only affected by annual and growth period rainfall but also has a great relationship with rainfall distribution. Studies have shown that the combined application of organic and inorganic fertilizers can significantly increase wheat yield, and the yield increase effect is better in dry years than in wet years. The different types of organic fertilizers and the ratio of chemical fertilizers also have different effects on wheat yield, indicating that the combined application of organic and chemical fertilizers and rainfall annual type have an important impact on dryland wheat yield [32]. This study shows that compared with a single application of chemical fertilizer treatment (F1, F2) and no fertilizer treatment (CK), applying 25,000 kg·hm⁻² of sheep manure increased oilseed flax yield by an average of 3.47–34.13% over two years. This is because when the experiment was carried out, the soil moisture content was low. With the increase in sheep manure input over two years, the moisture content also increased, which had a great effect on increasing yield levels.

5. Conclusions

This study shows that organic fertilizers can significantly increase soil moisture content and water storage of oilseed flax, reduce water consumption during the entire growth period of oilseed flax, regulate stage water consumption of oilseed flax, and increase oilseed flax seed yield and water use efficiency. Applying 25,000 kg·hm⁻² of sheep manure treatment significantly increased the thousand-grain weight, yield, and water use efficiency of oilseed flax by 14.70%, 48.32%, and 61.29%, respectively. It is a suitable high-yield and efficient green fertilization technology for oilseed flax production in the dryland agricultural area of the northwest Loess Plateau. Due to the influence of external factors such as different experimental years, different soil types, and different planting systems on the experimental results, in order to further understand the impact of organic fertilizers on soil moisture characteristics in the semi-arid areas of the Loess Plateau, it is necessary to conduct further long-term experiments. The research significance of long-term experiments will be greater.