LI Hui, XUE Jian-fu, GAO Zhi-qiang, XUE Nai-wen, YANG Zhen-ping

College of Agriculture, Shanxi Agricultural University, Taigu 030801, P.R.China

1. Introduction

Wheat (Triticum aestivumL.) is one of the three indispensable food crops largely consumed in China. And dryland wheat represents an important fraction of the agricultural production in Northwest China. It has been shown that yield of dryland winter wheat is strongly influenced by soil moisture (Nielsen and Vigil 2010), which is greatly influenced by the lack of precipitation uniformity during growing seasons. Current farm management practices (e.g.,soil tillage and film mulching) affect the physical, chemical,and biological properties of soil, in turn changing the soil moisture distribution. However, soil moisture storage and preservation ability can be salvaged with the appropriate tillage and sowing practices (Williams 2008).

Studies have shown that adoption of subsoiling (SS) can improve soil water storage (SWS) at sowing by decreasing soil bulk density and increasing soil porosity (Al-Adawi and Reeder 1996; Schiettecatteet al. 2005; Sunet al.2015b). Zhaoet al. (2013) showed that SS increased SWS in 0–300 cm soil profile compared to no tillage (NT) at sowing. Houet al. (2009) also concluded that SWS under SS treatment was significantly higher than that under NT.However, contrary results have shown that NT was more effective in increasing soil moisture than SS, where NT improved SWS by 3.0% compared to SS at sowing (Wanget al. 2009). These differences may have been caused by differences in precipitation. In addition, Houet al. (2009)reported that water use efficiency (WUE) in dryland winter wheat for SS was higher than that for NT, while soil water consumption during the growing season was larger for SS treatment compared to NT treatment. Increases in soil water consumption during growth periods has been shown to be related to the increases in SWS and the reduction of soil evaporation. Adoption of SS and NT has been shown to increase 47 mm of soil water consumption compared to traditional tillage, but no significant difference was found between SS and NT (Wanget al. 2003). Moreover,numerous studies have demonstrated that SS can increase grain yield through an increase of spike and kernels per spike from the anthesis stage to maturity (Liet al. 1999;Zhaoet al. 2013; Sunet al. 2015b). Consequently, adoption of SS is an effectively method to increase precipitation capture, thus increasing the yield of dryland winter wheat(Zhaoet al. 2013).

Plastic film drill sowing (FM) can preserve soil moisture by trapping precipitation below plastic mulch. Numerous studies have indicated that film mulching on the soil surface can conserve precipitation and effectively decrease soil water evaporation at the soil surface, resulting in increasing SWS (Chakrabortyet al. 2010; Zhouet al. 2011). Houet al.(2013) reported that film mulching can increase soil water use from deep soil layers, consequently improving grain yield of winter wheat, particularly during dry years. Drill sowing with plastic film mulching has been reported as one of the most available methods to increase water use efficiency (WUE) and yield in rain-fed regions (Liuet al.2009). This may be due to the increase of spike numbers for FM compared to no mulch (Liet al. 2008). However,contrary to this result, Liet al. (2001) reported that FM led to insufficient spike number, causing crop yield reduction.

The aforementioned studies have shown that adoption of SS and FM has a strong effect on SWS and yield for dryland winter wheat. However, there are few studies discussing the interaction between tillage during summer fallow and sowing method on SWS and yield for dryland winter wheat. We posit that tillage during summer fallow coupled with sowing practices will improve SWS and yield of dryland winter wheat. The objectives of this study were(i) to assess the effect of tillage during summer fallow and sowing methods on soil water storage, (ii) to evaluate the effect of tillage during summer fallow and sowing methods on soil water consumption, and (iii) to study the effect of tillage during summer fallow and sowing methods on the yield of dryland winter wheat.

2. Materials and methods

2.1. Experimental site

The experiment was conducted from July 2011 to June 2013 in the Wenxi Experimental Station of Shanxi Agricultural University (111°22′E, 35°35′N) in Shanxi Province, located in the Loess Plateau, China. The region has a temperate continental monsoon climate with a mean annual temperature of 12.6°C, a mean annual precipitation of ～440 mm, a potential evapotranspiration of 1 838.9 mm, and a sunshine duration of 2 461 h. The experimental field soil was classified as silty clay loam. The basic soil properties in the 0–20 cm layers were 11.88 g kg–1of organic matter, 38.62 mg kg–1of available nitrogen, and 14.61 mg kg–1of available phosphorus prior to sowing in 2011 to 2012 growing season.During the 2012 to 2013 season, the basic soil properties in the 0–20 cm layer were 12.72 g kg–1of organic matter,36.78 mg kg–1of available nitrogen, and 16.20 mg kg–1of available phosphorus. The precipitation at the experimental site was shown in Table 1. And according to the annual precipitation type division standard of Zhanget al. (2008),the 2011–2012 growing season was considered as a wet year, but the 2012–2013 growing season was consideredas a dry year.

2.2. Experimental design

The experiment was conducted in a split plot design with tillage during summer fallow as the main plot and sowing methods as the subplots. The tillage practices included subsoiling (SS) and no tillage (NT) during summer fallow.The sowing methods included conventional drill sowing(DS) and plastic film drill sowing (FM). The subplots were 40 m×3 m. And each treatment had three replications.The subsoiling was conducted during summer fallow after a heavy rain on July 10, 2011 and July 15, 2012 for two experimental years, respectively. And 1 500 kg ha–1of commercial organic fertilizer were applied to each treatment before tillage. Subsequently, the field was rotovated once again and leveled on August 25, 2011 and August 25, 2012.And then 150 kg N ha–1, 75 kg P2O5ha–1, and 75 kg K2O ha–1were applied to each treatment before sowing. And winter wheat was sown on October 1 for both experimental years. The cultivar was Yunhan 20410. The sowing rate was 97.5 kg ha–1.

The winter wheat was sown into rows spaced 20 cm apart for DS treatment. For the FM treatment, ridge formation along the crop rows, plastic film mulching, sowing, and compaction were implemented simultaneously. And the ridges had a 40-cm wide base and a 10-cm height with a circular arc. The plastic mulch was 400 mm wide and 0.01 mm thick plastic film. The furrow was 40 cm wide and created by a seed-furrow opener. And the plastic film was mulched concurrently into the soil along both sides of the fringe. Then the winter wheat was sown on the furrow at a spacing of 20 cm apart.

2.3. Sampling and analysis

Soil water storageSoil samples of 20 cm per soil layer were collected from 0–300 cm soil depth during the growth periods before sowing (BS), wintering stage (WS), jointing stage (JS), anthesis stage (AS), and mature stage (MS) of crop cultivation. And all soil samples were measuredviathe oven-drying method for soil gravimetric water content(SWC, %).

Soil water consumptionSoil water consumption during different growth periods of winter wheat was calculated with the soil water balance eq. (Wanget al. 2013a):

Where,ETi(mm) is the soil water consumption during different growth periods,SWSi(mm) is the soil water storage at the beginning of growth,SWSi+1(mm) is the soil water storage at the end of the growth period,Pi(mm) is the precipitation amount during the growth period. Fields were not irrigated and the underground water level was below five meters. If surface runoff and downward flux below the wheat root zone are ignored, the drainage at the site is negligible for soil water measurements (Maet al. 2015).

Precipitation use efficiencyPrecipitation use efficiency(PUE) indicated the crop use efficiency of the available precipitation. This was calculated with the following eq.:

Where, PUE (kg ha–1mm–1) is the precipitation use efficiency, Y (kg ha–1) is the grain yield, and P (mm) is the precipitation during the growing season.

Water use efficiencyWater use efficiency (WUE) was calculated with the following equation (Nealet al. 2011):

Where, WUE (kg ha–1mm–1) is the water use efficiency for grain yield, andETiis the total water consumption (mm).Contribution of soil water accumulation and consumption to yieldYield has been shown to improve with increasing SWS at sowing and soil water consumption during the growth period (Wang 2003).

Where,ΔY1(kg ha–1mm–1) is the yield increase that results in per soil water storage andΔY2(kg ha–1mm–1) is the yield increase that results in per soil water consumption;

Y1andY2are yields under different treatments (kg ha–1);W1andW2are the soil water storage at sowing under different treatments (mm);E1andE2are soil water consumption values during the growth period under different treatments(mm).

Determination of grain yield and the factors that contributed to yieldThe grain yield and the factors that contribute to yield included spike number per unit at the site, kernel per spike, and the 1 000-grain weight at the maturity stage. Twenty plants of winter wheat were randomly selected from each plot to calculate biological yield. Lastly,wheat from plots with a total of 20 m2was harvested to ascertain the economic grain yield.

2.4. Statistical analysis

The influence of film mulching during the summer fallow season and sowing methods on the yield and factors for dryland winter wheat was statistically measured using SPSS 16.0 (SPSS Inc., Chicago, IL, US). The differences in means among the four treatments were compared using a one-way analysis of variance with Duncan’s new multiple range test atP＜0.05 level. The figures were made using Sigma Plot 12.0 (Systat Software, Inc., San Jose, CA).

3. Results

3.1. Soil water storage

Water storage at sowing showed a variable trend during both seasons. At relative upper level of soil, the SWS showed a decreasing trend with increasing soil depth for both experimental years (0–100 cm for 2011–2012 and 0–120 cm for 2012–2013). However, at relative deep level of soil, the SWS showed a decreasing trend (180–300 cm)during 2011–2012 growing season and an increasing trend (120–300 cm) during 2012–2013 growing season with increasing soil depth (Fig. 1). The SWS at sowing for SS×FM was significantly higher than that for SS×DS,NT×DS, and NT×FM by 0.37, 9.25, and 9.75% in wet year,and by 10.60, 16.07, and 1.83% in dry year, respectively.

At maturity of the 2011–2012 growing season, adoption of SS×FM treatment exhibited lower SWS than the other three treatments, while the NT×DS treatment showed the highest SWS among all treatments. During the 2012–2013 growing season, SWS for all treatments declined in the 0–160 cm soil layer and increased in the 160–300 cm layer at maturity.

3.2. Soil water consumption

TheETiof WS–JS and JS–AS for the FM treatments were significantly higher than that for DS treatments (P＜0.05)during the 2011–2012 growing season (Table 2). However,theETiof WS–JS and JS–AS for FM treatments was significantly lower than that for DS treatments (P＜0.05)during 2012–2013 growing season, respectively. During the 2011–2012 growing season, theETiof WS–JS for SS×DS was significantly lower than that for NT×DS by 7.6%,(P＜0.05), and theETiof WS–JS for SS×FM was significantly lower than that for NT×FM by 20.3%(P＜ 0.05). However, the differences ofETiof WS–JS between DS and SS treatments were not significant during 2012–2013 growing season. TheETiof JS–AS for SS treatments were significantly higher than that for DS treatments in both two growing seasons.Furthermore, theETiof AS–MS of SS×FM was significantly higher than that for SS×DS by 76.0%, while theETiof AS–MS for NT×FM was significantly higher than that for NT×DS by 79.0% (P＜0.05) during the 2012–2013 growing season.However, the differences forETiof AS–MS between the FM and DS treatments were not significant during 2011–2012 growing season.

Fig. 1 Soil water storage in 0–300 cm soil layers at sowing and at maturity in 2011–2012 and 2012–2013 growing seasons.SS×DS indicated the treatment of subsoiling during summer fallow with conventional drill sowing; SS×FM indicated the treatment of subsoiling during summer fallow with plastic film drill sowing; NT×DS indicated the treatment of no-tillage during summer fallow with conventional drill sowing; and NT×FM indicated the treatment of no-tillage during summer fallow with plastic film drill sowing.Bars are SE.

The correlation coefficients betweenETiand yield showed that theETiof WS–JS, JS–AS, and AS–MS were significantly and positively correlated with yield of dryland winter wheat at the 0.01 level (Table 3). It was also observed that theETiof WS–JS and AS-MS were significantly and positively correlated with spike number and 1 000-grain weight at the 0.01 level, andETiof JS–AS was positively correlated with spike number at the 0.05 level. However,the correlation betweenETiand kernels per spike was not significant.

3.3. Water use ef ficiency and precipitation use efficiency

The results showed that both SS treatments and FM treatments can increase PUE and WUE (Table 4).Furthermore, PUE was significantly higher for SS×FM than that for SS×DS, NT×FM, or NT×DS by 13.1, 14.3, 47.3%and 39.0, 25.9, 35.6% during both seasons, respectively(P＜0.05). Thus, subsoiling during summer fallow and film mulching were beneficial for utilization and retention of precipitation, particularly during dry years. There was no significant difference in WUE among SS×DS, SS×FM, and NT×FM during the 2011–2012 growing season, but the WUEfor these treatments were higher than that for NT×DS by 16.5, 22.8, and 23.0%. However, WUE for SS×FM was the maximum during the 2012–2013 growing season and was significantly higher than NT×FM, SS×DS, and NT×DS by 8.1, 38.9, and 39.2%, respectively. Overall, the effect of SS and FM treatments on WUE was not apparent in wet years but strong during dry years.

Table 2 Total water consumption in 0–300 cm soil layers and proportional contributions of soil water consumption (ETi) to total water consumption under the treatments

Table 3 Correlation coefficients between soil water consumption (ETi) during growing periods and yield and its components

Table 4 The effects of tillage and sowing methods on soil water and precipitation use efficiency1)

3.4. Wheat yield and its components

Grain yield and its components (kernel per spike, 1 000-grain weight, and spike number) were higher during the 2012–2013 growing season than those during the 2011–2012 growing season (Fig. 2). No significant difference was observed for kernels per spike among all treatments and during both seasons. The 1 000-grain weight showed no significant difference among all treatments during the 2011–2012 growing season. However, the 1 000-grain weight for SS×FM was significantly higher by 32.2%compared to NT×DS during the 2012–2013 growing season. Furthermore, spike number for FM treatments was significantly higher than that for DS treatments during both seasons. Similarly, the yield for FM treatments was significantly higher than that for DS treatments during both seasons. Furthermore, the results showed that the yield for SS×FM treatment was higher than that for NT×FM, SS×DS,and NT×DS by 13.1, 14.4, and 47.3% (2011–2012) and 25.9, 39.1, and 35.7% (2012–2013), respectively. Moreover,NT×DS had the smallest yield in both seasons.

The contribution of soil water accumulation and consumption on yield is shown in Table 5. During the 2011–2012 growing season, the grain yield for SS×FM improved by 294.3, 35.8, and 13.4 kg ha–1with the increase of 1 mm SWS at sowing compared to SS×DS, NT×DS, and NT×FM treatments, respectively. It is obvious that SS×FM offered an effective method to increase yield through improving SWS at sowing during wet years. Similarly, the yield for SS×FM improved by 13.4, 8.7, and 52.4 kg ha–1with the increase of 1 mm SWS at sowing compared to SS×DS, NT×DS, and NT×FM during 2012–2013 growing season. Overall, grain yield increased with increasing SWS at sowing for SS×FM.

In addition, grain yield increased by enhancing soil water consumption of the growth period for SS×FM compared to other treatments during wet years. However, the yield for SS×FM was reduced by 67.2 kg ha–1with 1 mm increment of soil water consumption during the growth period compared to SS×DS. Furthermore, during the 2012–2013 growing season, increasing soil water consumption during the growth period by 1 mm for SS×FM improved yield by 12.0, 11.4,and 3.3 kg ha–1compared to SS×DS, NT×DS, and NT×FM,respectively. Overall, adoption of SS×FM can improve yield more than other treatments through increasing soil water consumption during growth period.

Fig. 2 The yield and its components under different treatments in 2011–2012 and 2012–2013 growing seasons. SS×DS indicated the treatment of subsoiling during summer fallow with conventional drill sowing; SS×FM indicated the treatment of subsoiling during summer fallow with plastic film drill sowing; NT×DS indicated the treatment of no-tillage during summer fallow with conventional drill sowing; and NT×FM indicated the treatment of no-tillage during summer fallow with plastic film drill sowing. Lowercase letters indicate statistical difference among treatments at P＜0.05. Bars are SE.

Table 5 The contribution of soil water accumulation and consumption to yield under subsoiling in summer fallow season and film mulching at sowing

4. Discussion

Sufficient soil moisture at pre-sowing has been shown to be a prerequisite for high yield of dryland wheat, while low moisture content at sowing resulted in the final reduction of yield (Wanget al. 2016). Study showed that subsoiling significantly increased grain yield and WUE, especially when subsoiling was applied during summer fallow (Maet al.2015). Because adoption of subsoiling can break the plow pan and improve precipitation infiltration to increase SWS at sowing and PUE (Pavel 2011; Zinket al. 2011; Sunet al.2013). Beyond tillage of subsoiling, some studies showed that film mulching increased the capacity for soil moisture preservation by 108.4 mm compared to bare soil, thus realizing 73.2% of soil water storage efficiency, resulting in increased SWS at sowing (Chenet al. 2015). In this study, adoption of SS×FM during dry years had a greater impact on SWS at sowing than during wet years. This was because the soil moisture was sufficient and nearly saturated during wet years, making it difficult to use precipitation as a metric. However, withholding more precipitation in dry years compensated for the lack of indispensable moisture for growth. According to a study reported, SS×FM decreased the evapotranspiration at sowing and increased soil water storage (Sunet al. 2015a). In addition, spike number and yield of dryland winter wheat significantly correlated with pre-sowing soil water, and consequently, yield increased by 40.8% on average with the improvement of SWS at sowing(Wang 2003). In this study, an increase of 1 mm of SWS at sowing for SS×FM improved yield by 3.30–294.27 kg ha–1in both seasons compared to other treatments. The increase of SWS at sowing was a basic requirement for soil water utilization, enabling the formation of spikes and winter wheat filling in later growth period, ultimately increasing yield.

Soil water consumption was a progress for crop to absorption soil moisture, and the variation of SWS in growth periods influenced crop growth, resulting influencingETiin different growth periods. Adoption of SS×FM treatments significantly increasedETiof JS–AS in wet year, but theETiof WS–JS and AS-MS for SS×FM were significantly lower than that for NT×FM (P＜0.05). In the study, theETiof WS–JS, JS–AS, and AS–MS were significantly and positively correlated with spike number and yield of dryland winter wheat. TheETiof JS–AS was the main growth period for winter wheat to develop a spike, and the water consumption of JS–AS satisfied the primary moisture demand of winter wheat to form the spike as well as for booting, eventually increasing spike number and grain yield during wet years (Wanget al. 2013b). In addition,increasing 1 mm of soil water consumption during the growth period for SS×FM improved yield compared to other treatments in both seasons except for SS×DS. The yield declined with increasing 1 mm of soil water consumption of growth period for SS×FM compared to SS×DS. Similar results were reported by other studies. Chenet al. (2016)showed that the grain yield for FM treatments increased by 10.6–11.4 kg ha–1with 1 mm increment of SWS at sowing,and increased by 22–26 kg ha–1with 1 mm of soil water consumption during the growth period. Liet al. (2013)reported that grain yield for FM treatments increased when soil water consumption was improved during the growth period. Differences between the result of these studies may be caused by lower soil water consumption of growth period for SS×FM than for SS×DS, which is because mulching plastic film reduced soil evaporation compared to drill sowing without mulching (Chenet al. 2016), especially under the same tillage practice. Moreover, the yield increment during wet years along with the increasing SWS at sowing and soil water consumption during the growth period was significantly higher for SS×FM than during dry years, and improving SWS at sowing increased the yield rather than enhancing soil water consumption during the growth period.Overall, the yield increment was based on high SWS at sowing and soil water consumption during the growth period,and a large quantity of precipitation was the foundation to increase SWS at sowing.

In this study, the yield and its components were the highest for SS×FM, and adoption of SS×FM played an important role to utilize the available soil water to improve spike number,especially during dry years. Moreover, adoption of SS×FM significantly increased the precipitation use efficiency for dryland winter wheat, which had a higher WUE than other treatments (P＜0.05). No significant difference was found for 1 000-grain weight and kernels among all treatments.However, Zhaoet al. (2013) showed that kernels per spike,spike number, and 1 000-grain weight for SS treatments were significantly higher than those for NT treatments. This may be because subsoiling was implemented in the 15th day after harvest in the study by Zhaoet al. (2013), which was sooner than that in this study. Above all, the treatment of SS×FM was an effective solution to enhance SWS at sowing and it was an optimized soil management practices to improve WUE and yield for dryland winter wheat.

5. Conclusion

Subsoiling during summer fallow increased the SWS at sowing in wet year, and plastic film drill sowing increased the SWS at sowing in dry year. Adoption of SS×FM significantly improved SWS at sowing than other treatments in two years.And grain yield increased with increasing SWS at sowing for SS×FM was significantly higher than other treatments. TheETiof WS–JS, JS–AS, and AS–MS were significantly and positively correlated with yield of dryland winter wheat. The treatment of FM significantly improved theETiof JS–AS, and adoption of SS significantly improved theETiof JS–AS. Also yield and spike number of SS×FM were significantly higher than those for other treatments in both two experimental years. Overall, subsoiling during summer fallow and drill sowing with plastic film was an optimized soil management practices to improve WUE and yield for dryland winter wheat in Loess Plateau of China.

Acknowledgements

This research was supported by the Special Fund for Agro-scientific Research in the Public Interest, China(201303104), the earmarked fund for China Agriculture Research System (CARS-03-01-24), and the Project Funded by China Postdoctoral Science Foundation (K461501024).

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