Proper border length can improve soil water distribution, promote 1 grain yield of winter wheat, and potentially save water resources

8 With water resources becoming scarcer and a growing demand for increased 9 food supplies, there is an urgent need to maximize the efficiency of irrigation systems. 10 We aimed to find a suitable border length to reduce the quantity of irrigation water 11 through a traditional border irrigation system and, thus, alleviate groundwater 12 depletion in Huang-Huai-Hai Plain (3HP). A 2-year experiment (2017–2019) was 13 conducted in 3HP, which three border lengths were tested: 15 m (L15), 25 m (L25), 14 and 35 m (L35); supplementary irrigation was implemented during jointing and 15 anthesis, inflow cutoff was set at 90%, and set a control treatment without irrigation 16 (CK). The results showed that L25 significantly improved soil water distribution after 17 irrigation, and increased soil water consumption compared with L15 and L35. The the 18 dry matter accumulation post-anthesis was also higher in L25 than in the other 19 treatments, as well as the WUE. The correlation analysis of soil water content after 20 irrigation with yield confirmed that L25 was more conducive to high grain yield. 21 Hence, under these test conditions, the irrigation field treatments with a border length 22


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The production of China's wheat in 2016 was approximately 129 million tons, of 28 which more than 60% originated from Huang-Huai-Hai Plain (3HP); however, water 29 resources in this area accounted for only 7% of China's total 1,2 . Because of the 30 monsoon climate affecting this region, the precipitation is mainly concentrated in 31 summer, which is insufficient to meet the water requirements for this region (400-500 32 mm) 3,4 . Since this has become an important limiting factor for the yield of wheat 33 production 5 , groundwater irrigation has been the main strategy employed to solve this 34 problem 6 . However, inefficient irrigation techniques lead to the waste of water 35 resources and the consequent depletion of groundwater levels, which prevents the 36 development of sustainable wheat production systems 7 . Therefore, there is an urgent 37 need to optimize irrigation techniques to improve water efficiency 8 . 38 Because of its low cost and unchallenging implementation, traditional border 39 irrigation is still the principal irrigation method used in the 3HP 9 . Studies show that 17.15% and 6.09%, respectively 12 . Other studies have shown that when the border 45 length was between 80 m and 100 m, the single irrigation amount was generally 46 approximately 100-150 mm. Thus, excessive border length leads to excessive 47 irrigation and consequently a significant reduction in WUE 13 . In fact, the extensive 48 research conducted by Wang et al. at 3HP showed that during the wheat growing 49 season, the average irrigation amount is 101.8 mm, ranging between 51 mm and 172 50 mm, which is sufficient to ensure wheat yield 14 . However, a survey of approximately 51 300 plots in Huimin, Shandong Province, revealed that the border lengths of 87% of 52 the irrigation fields were longer than 100 m, illustrating that excessive border length 53 was a common problem in this area 15 . Therefore, it is necessary to shorten the fields' 54 border length to reduce the amount of irrigation and improve its uniformity.

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Nevertheless, a field experiment is needed to determine the appropriate border length 56 of irrigation fields.

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More than 70% of the grain yield of wheat is owing to the accumulation of 58 photosynthetic products after anthesis, and the soil water condition can significantly 59 affect the accumulation of dry matter 16,17 . Drought after anthesis will have a negative 60 effect on photosynthesis by shortening its duration and reducing the accumulation of 61 photosynthetic product 18 . Indeed, a treatment of 70%-75% soil water content showed 62 a significantly higher net photosynthetic rate of flag leaves after anthesis, as well as 63 an increase in dry matter accumulation, than with a treatment of 50%-55% soil water 64 content 19 . Underwater stress conditions can promote wheat grain filling and increase 65 dry matter accumulation during maturity, while excessive irrigation can reduce the 66 4 distribution of dry matter in the grains after anthesis, thereby reducing grain yield 20,21 .

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For example, Ren et al. found that a field treatment with a 65% water holding 68 capacity had significantly higher levels of dry matter accumulation and grain yield 69 than those of a field treatment with a water holding capacity of 80% 22 . Moreover, the 70 effect of soil water stress on dry matter accumulation and distribution is relatively

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Irrigation amount 82 The irrigation amount increased significantly with the increase of border length.

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In the two growing seasons, the irrigation amount of L25 was lower than that of L35 84 by 27.66 mm on average, which in turn was superior to that of L15 by 18.36 mm on 85 average ( Fig. 1). Soil water content and distribution after irrigation 91 The results obtained for the two growing seasons were consistent. Compared 92 with CK, soil water content increased significantly after irrigation. Soil water content 93 was the highest in L35, followed by L25 and L15 (Fig. 2). Within each treatment, the 94 soil water content gradually decreased from sections A to G. Still, there was no 95 significant difference in the distribution of soil water in L25 and L15, apart from L35 96 where the soil water content of the latter section was significantly lower than that of 97 the front section. After irrigation, the coefficient of variation of soil water content in 98 L25 and L15 was significantly lower than that of L35 (Table 3).     120 The highest ET value was observed in L35, followed by L25, L15, with CK 121 presenting the lowest value. The ratio of irrigation water amount to ET under L25 and 122 L15 was significantly lower than that under L35. The ratio of precipitation amount to 123 ET decreased in the order L35 < L25 < L15 < CK. There was no significant difference 124 8 between L25 and L15 in the ratio of W to ET, which were both significantly higher 125 than that of L35 (Table 4). Dry matter accumulation post-anthesis (DMPA) and its contribution to grain 130 (CR) 131 The DMPA and CR were the lowest in CK in the two growing seasons. DMPA of 132 L25 was significantly higher than that of L35 and L15, and CR of L15 was 133 significantly lower than that of the other treatments. In 2018-2019, DMPA and CR 134 values were the highest in L25 (Fig. 4).

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Compared with CK, the irrigation treatments significantly improved grain yield 155 and WUE (Fig. 6). In 2017-2018, CR of L25 was 5.90% higher than L15 and 4.36% 156 higher than L35. In 2018-2019, this value in L25 was 5.92% higher than L15 and 157 3.18% higher than L35. There was no significant difference in WUE between L25 and 158 L15, although it was higher than that of L35.

Correlation analysis of soil water content after irrigation with grain yield and
165 dry matter accumulation 166 The dry matter accumulation at maturity and grain yield have a quadratic 167 relationship with the water content of the 0-40 cm soil layer after irrigation (Fig. 7).

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Additionally, the correlation analysis between grain yield and soil water content 235 15 in the 0-40 cm soil layers confirmed that L25 was more conducive to a higher yield.

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Because the water stress of L15 can improve the translocation of dry matter, and thus, 237 decrease dry matter accumulation after anthesis, its grain yield was significantly lower 238 than that of L25. The grain yield of L35 was lower than that of L25. Therefore, L25 239 was considered the best irrigation border length for both high yield and water saving 240 in this experiment.    (35°42′N, 116°41′N), which experiences a warm 274 temperature continental climate. This area has a light foam soil type. And Table 1 275 shows nutrient content in 0-20 cm soil layer, and Table 2