Mulching measures improve soil moisture in rain-fed jujube orchard in the loess hilly region of China

3 Background: Water shortage is the main bottleneck restricting the healthy and sustainable 4 development of rain-fed jujube orchards in the loess hilly region of China. Given the 5 functions of mulching on soil moisture conservation, evaporation reduction, and water use 6 efficiency improvement, maize straw mulching (SM) and pruned jujube branch mulching 7 (BM) were applied to rain-fed jujube orchards in this study. Soil moisture dynamics, soil 8 water storage, water consumption, and soil moisture attenuation after typical rainfall under 9 SM, BM, and clean tillage (CT) were systematically studied. 10 Results: (1) The 0-60 cm soil layer was the seasonal fluctuation layer of soil moisture 11 under SM, BM, and CT in both the normal precipitation year and the dry year. The 0-60, 12 60-160, and 160-280 cm soil layers under CT all obtained the lowest soil moisture content 13 in the three experimental years. The soil moisture content of each soil layer under SM and 14 BM was higher than that under CT, and SM showed the most obvious effect of increasing 15 soil moisture. (2) SM and BM showed significant soil water storage effect in all the jujube 16 growth stages in both the normal precipitation year and the dry year, and SM had a better 17 water storage effect than BM. (3) SM and BM reduced the water consumption amount in 18 each jujube growth stage. SM reduced water consumption amount by 94.3, 60.8, and 19 121.3 mm compared with CT in the whole growth period of jujube in 2014, 2015, and 20 2016, respectively. The water consumption amount of BM decreased by 34.8 mm and 31.0 21 mm respectively compared with that of CT in the whole growth period in 2014 and 2015. (4) CT had the maximum soil moisture loss rate under continuous drought after rainfall. 23 The soil moisture loss rate of CT was above 37.3% on the eleventh day after the typical 24 rainfall in 2014, 2015, and 2016. With the extension of drought, the soil moisture loss rate 25 under SM increased slowly, while it increased rapidly under CT. 26 Conclusion: This study suggests that straw mulching is the best mulching measure for 27 rain-fed jujube orchards, and the pruned jujube branches can also be used for in-situ 28 mulching, which can also obtain a certain moisture conservation effect. 29 Review & Editing, Project administration. Conceptualization, Resources,


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The loess hilly region of China is characterized by the dry climate, strong 32 evaporation, scarce precipitation and uneven seasonal distribution, and the mismatch 33 between natural precipitation and crop water demand (Yang et al., 2018;Feng et al., 2020). 34 The topography of the loess hilly region is dominated by sloping land, many of which 35 have great gradient and loose soil structure, resulting in serious soil erosion (Song et al.,36 2018; Yang and Lu, 2018). In addition, there is little irrigation in the loess hilly region, and  (Jin et al., 2018). How to reasonably and efficiently utilize the limited 40 natural precipitation in the loess hilly region has become the focus and main trend. 41 As the main economic forest and ecological forest for soil and water conservation in 42 the loess hilly region, the jujube cultivation area has expanded rapidly in recent years, and 43 4 it has exceeded one million hectares (Chen et al., 2014;Ling et al., 2017). The traditional 44 clean tillage is currently widely used in jujube orchards, that is, weeds are manually 45 removed many times and the soil is not loosened during the jujube growth period (Huang 46 et al., 2016). Clean tillage has the advantages of pest control and seedling raising for 47 orchard, with good short-term effects. However, many studies have found that long-term 48 clean tillage will cause serious soil erosion, a decline in soil fertility, deterioration of soil 49 properties, destruction of ecological balance, and ultimately lead to premature ageing of 50 fruit trees, reduction of fruit yield, and deterioration of fruit quality, which is not 51 conducive to the sustainable development of orchards (Pearson, 2002;Hao et al., 2016;52 Mikha et al., 2017). 53 As an effective soil management measure in rain-fed areas, mulching has been 54 recognized and widely used in many countries. Mulching has the functions of conserving 55 soil moisture, reducing evaporation, improving soil fertility, adjusting soil temperature, 56 etc., which is beneficial to promote crop growth and water use efficiency (Kader et  soil fertility, regulate soil temperature, stimulate soil microbial activity, have a positive 5 impact on fruit tree growth, fruit yield and quality, and improve water use efficiency.

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Based on the above background, maize straw and pruned jujube branches were used 67 to cover the soil surface of the rain-fed jujube orchard in the loess hilly region, and the 68 impact of these two mulching measures on soil moisture was studied. The findings can  The experiment was conducted at the Jujube Demonstration Bases (37°15′N，110°75 21′E) in Dianzegou Town, Qingjian County, Yulin City, Shaanxi Province, China, which 76 is located in the loess hilly region. The climate of the study site belongs to the warm 77 temperate continental monsoon semi-arid climate, with annual average precipitation of 78 505 mm, of which the precipitation from June to August accounts for about 80% of the 79 total annual precipitation (Fig. 1). The annual average air temperature at the study site is 80 9.6℃, with an average air temperature of -6.8℃ in January and 23.8℃ in July (Fig. 1).

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Both the air temperature difference between day and night and the air temperature change 82 in seasons is great. The study site has abundant sunshine, with an annual average sunshine 83 duration of 2720 hours and frost-free period of 160-170 days. and the year when the precipitation decreases more than 10% than the annual average 93 precipitation during the crop growth period is the dry year. Therefore, 2014 and 2016 were 94 classified as normal precipitation years, and 2015 was a dry year. The soil at the study site 95 is loessal soil, belonging to silt loam, with a loose structure and strong infiltration capacity.

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The main physical properties of the 0-100 cm soil layer at the study site are shown in 97   Table 1.    Three treatments were designed, namely, straw mulching (SM), jujube branch 120 mulching (BM), and clean tillage (CT). Each treatment was repeated twice, and a total of 121 six experimental plots were studied. The mulching material of SM was maize straw, the 122 mulching thickness was 15 cm, and maize straw was supplemented at the end of the jujube 123 growth period every year to ensure the designed mulching thickness. The pruned jujube 124 branches were broken to 10 cm in length under BM, and the mulching thickness was also 125 10 cm. The soil surface under CT was exposed without any mulching measures. about 280 mm of precipitation, much higher than the maximum precipitation in the study 164 area, so the deep percolation will not occur after rainfall, that is, D=0. Jujube trees were 165 pruned every April, and the invalid rainfall with daily rainfall less than 5 mm was ignored 166 when the effective rainfall was counted, so the canopy interception is negligible, that is,

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IN=0. The calculation equation of ET can be simplified as: The water consumption percentage (CP) was obtained according to Huang et al.

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(2013) as follows: where WC i represents water consumption of jujube trees in the i-th growth stage (mm), 173 and WC T is the total water consumption in all growth stages (mm).

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Soil moisture loss rate (SMLR) was estimated from the following equation ( where SMC 1 represents the soil volumetric moisture content on the first day after 178 rainfall, and SMC n+1 represents the soil volumetric moisture content on the (n+1)-th day 179 after a rainfall.   The soil moisture content of the fine root diffuse layer was mainly affected by the 216 distribution density of fine roots and was weakly affected by rainfall (Fig. 4b). SM had the affected by rainfall (Fig. 4c). The soil moisture content of the fine root sparse layer under 222 CT was lower than the wilting moisture in three growing seasons, forming a perennial low 223 humidity zone. The soil moisture content of the fine root sparse layer under the mulching 224 treatments (SM and BM) increased by 6.11%-7.80% compared with CT (p < 0.05). of SM and BM was 41.5% and 38.9% higher than that of CT in 2014, 60.4% and 49.0% 237 higher than that of CT in 2015 (Fig. 5a, b). Soil water storage under SM was still 105.4 238 mm higher than that under CT in 2016 (Fig. 5c). The effect of SM on increasing moisture 239 at each growth stage was better than that of BM in three experimental years. treatment showed a decreasing trend as the growth stage progressed (Fig. 5b, c).  The water consumption amount and water consumption percentage of the 262 experimental rain-fed jujube orchard were significantly different in different growth stages 263 (Table 2). In the emerging and leafing stage, the water consumption amount of jujube trees 264 under SM and BM was less than that under CT, which decreased by 4.3%-13.7% and  On the third day after all typical rainfalls, the soil moisture of the infiltration layer 309 under all experimental treatments showed attenuation (Fig. 6). CT had the maximum soil 310 moisture loss rate with 9.0% and 13.2% in 2014 and 2015 (Fig. 6c, f), and SM had the 311 minimum value with 8.0% and 4.3% in 2014 and 2015, respectively (Fig. 6a, d). The soil 312 moisture loss rate of the three experimental treatments was 5.5%-6.0% without a 313 significant difference in 2016 (Fig. 6C). On the seventh day after typical rainfall, the 314 maximum soil moisture loss rate was obtained by CT with 23.8%, 30.7%, and 19.7% in 315 2014, 2015, and 2016, respectively (Fig. 6c, f, i). The soil moisture loss rate under BM 316 was the second, and that under SM was the lowest, only 17.1%, 8.7%, and 14.3% in 2014, 317 2015, and 2016, respectively (Fig. 6a, d, g). Compared with the soil moisture loss rate on 318 the third day after typical rainfall, the soil moisture loss rate on the seventh day under CT 319 increased significantly, with the increments all being above 14.2% in the three 320 experimental years (Fig. 6c, f, i). The soil moisture loss rate under SM increased slowly, 321 especially in 2015, the increment was only 4.4% (Fig. 6d). With the prolongation of 322 drought after typical rainfall, the soil moisture loss rate of the three experimental 323 treatments continued to increase. On the eleventh day after the typical rainfall, CT still 324 maintained the maximum soil moisture loss rate, all above 37.3% from 2014 to 2016 (Fig.   325 6c, f, i). SM still maintained the minimum soil moisture loss rate, which was about 24.0% 326 in 2014 and 2016, and only 14.7% in 2015 (Fig. 6a, d, g). Compared with the soil moisture 327 loss rate on the seventh day after the typical rainfall, the increase rate of the soil moisture 328 20 loss rate on the eleventh day after the typical rainfall under CT was significantly higher 329 than that under the mulching treatments, which was above 11.4% in the three experimental 330 years (Fig. 6c, f, i), while the increase rate of the soil moisture loss rate under SM was 331 slow, not exceeding 9.7% (Fig. 6a, d, g).  60-160 cm soil layer was less affected by rainfall (Fig. 4b). The soil moisture in 160-280 346 cm soil layer was hardly affected by rainfall (Fig. 4c). The 160-280 cm soil layer under 347 CT formed a perennial low humidity zone in three experimental years (Fig. 4c), indicating 348 that the rain-fed jujube orchard did not form a soil reservoir that can regulate the jujube 349 growth under natural rainfall. Once in a dry year, the jujube growth is bound to be 350 21 adversely affected.

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As the drought continued after typical rainfall, the rain-fed jujube orchard covered 352 with straw and jujube branches had a lower soil moisture loss rate than the clean tillage 353 treatment (CT) (Fig. 6). The reason may be that the covering materials can effectively   (Table 2), and improve the soil 365 moisture environment in the rain-fed jujube orchard, which was consistent with previous 366 research results (Pan et al., 2018;Wang et al., 2018). In this study, straw mulching was 367 better than jujube branch mulching in improving the soil moisture environment in rain-fed 368 jujube orchard. Although jujube branch mulching can also intercept rainwater, store water 369 and reduce soil moisture evaporation, the number of branches pruned from jujube trees is

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In this study, soil moisture dynamics, soil water storage, water consumption, and soil 390 moisture attenuation after typical rainfall in rain-fed jujube orchards in the loess hilly 391 region under straw mulching (SM), jujube branch mulching (BM), and clean tillage (CT) 392 were studied, and the following results were obtained:

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(1) The 0-60 cm soil layer of rain-fed jujube orchard was the seasonal fluctuation percentage was more obvious than that of BM.

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(4) The soil moisture loss rate of CT was significantly higher than that of SM and 412 BM under continuous drought after rainfall. With the extension of drought, the soil 413 moisture loss rate under SM increased slowly, while it increased rapidly under CT.

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In conclusion, it is recommended to adopt mulching measures in rain-fed jujube 415 orchards to ensure efficient utilization of precipitation and sustainable development of 416 24 jujube orchards. Straw mulching is the best mulching measure, and the pruned jujube 417 branches can also cover the rain-fed jujube orchard in situ, which can achieve a certain 418 moisture conservation effect.