PEER-REVIEWED ARTICLE PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3637 Response of Corn Yield to Water Retaining Agents, Inhibitors, and Corn Stalks Addition in Semi-arid Cropland Kaikuo Wu,a Na Lv,a,b Wei Bai,c Yue Meng,a,b Mei Han,d Yan Xue,a Yuchao Song,a Xueshi Xie,e Tingting Wang,e Ping Gong,a,* and Lili Zhang a,* Drought, excessive use of nitrogen fertilizer, and decline in soil organic matter threaten corn production. This study investigated the potential of water retaining agents, inhibitors, and corn stalks in enhancing soil physicochemical properties to bolster corn yield in semi-arid farmlands. In our study, polyacrylamide addition increased the content of ammonium nitrogen (NH4 +-N) and nitrate nitrogen (NO3 --N) in the seedling stage, exchangeable potassium (K) in the mature stage but decreased the content of available phosphorus (P) in the seedling stage. Potassium polyacrylate addition increased the content of NH4 +-N and decreased the content of available P in the seedling stage. The addition of inhibitors decreased the content of NH4 +-N and available P in the seedling stage, NO3 --N and available P in the jointing stage, and NH4 +-N in the mature stage, respectively. Corn stalks returning could maintain soil moisture, decrease the content of NH4 +-N in the seedling stage and exchangeable K in the mature stage, and increase the content of available P and exchangeable K in the seedling stage. Combined application of inhibitors and corn stalks could increase soil organic carbon (SOC) and ensure corn yield, which was the best fertilization mode in semi-arid cropland. DOI: 10.15376/biores.19.2.3637-3652 Keywords: Polyacrylamide; Potassium polyacrylate; NBPT; DMPP; Corn stalks Contact information: a: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; b: University of Chinese Academy of Sciences, Beijing 100049, China; c: Liaoning Key Laboratory of Conservation Tillage in Dry Land, Tillage and Cultivation Research Institute, Liaoning Academy of Agricultural Science, Shenyang 110161, China; d: Industrial Transformation and Revitalization Service Center of Fuxin, Fuxin 123000, China; e: Stanley Agriculture Group Co. Ltd., Linshu, Shandong, 276700, China; *Corresponding author: llzhang@iae.ac.cn; gongping@iae.ac.cn; Kaikuo Wu and Na Lv contributed equally; INTRODUCTION Corn is one of the most important food crops in the world, providing at least 30% of food calories for 4.5 billion people in 94 developing countries worldwide (Tefera et al. 2016). China accounts for 21% of the world’s corn production (Xia et al. 2020). Liaoning Province is one of the 13 major grain-producing areas in China. The planting area of spring corn is more than 2 million hectares, of which the northwest area of Liaoning Province accounts for more than 2/3, and the output accounts for more than 75% of Liaoning Province. Therefore, corn production in the region is crucial for China’s food security (Zhe et al. 2020). However, this area belongs to semi-arid cropland with a record of water shortage, and long-term cultivation has led to the decline of soil organic matter, which restricts the production of corn (Meng et al. 2023; Rix et al. 2023). Therefore, measures PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3638 need to be taken to alleviate the constraints of these factors on corn production. Water retaining agents are substances that can be added to soil to alleviate crop loss caused by drought. Among these are polyacrylamide (PAM) and potassium polyacrylate (K-PAA), which are commonly used (Wu et al. 2018; Zhao et al. 2023). Moreover, water retaining agents have the characteristics of promoting plant growth and root secretion, increasing soil enzyme activity, etc., which may improve the transformation of nutrients in the soil and promote corn production (Zhang et al. 2020a). In addition to water limitation, nitrogen (N) is also one of the most critical elements affecting crop yield. However, excessive fertilization in production practices can lead to a serious imbalance between the available nutrients provided by soil and the actual needs of crops (Cui et al. 2022). To deal with this problem, urea inhibitors and nitrification inhibitors are added to fertilizers to regulate the transformation process of fertilizer N in soil (Scherer et al. 2014; Li et al. 2023). Urease inhibitors can delay urea hydrolysis by inhibiting urease activity. Nitrification inhibitors reduce the formation and accumulation of nitrate by inhibiting the conversion of ammonium (NH4 +) to nitrate (NO3 -) (Liu et al. 2023). The combined application of urease inhibitors and nitrification inhibitors is considered to have better yield increasing effects (Qi et al. 2022). However, maintaining high crop yields in the long term also requires fertile soil. To alleviate soil degradation and improve soil fertility, measures of returning straw to the soil (i.e. “straw returning”) have emerged (Zheng et al. 2021; Meng et al. 2023). Straw contains a large amount of lignocellulose, soluble carbon, and other nutrient elements, and it has good porosity (Thíebeau et al. 2021; Lu et al. 2023). These characteristics of straw are often used to improve soil physicochemical properties, promote soil moisture and fertilizer retention, and ensure crop yield (Velthof et al. 2002; Wu et al. 2021). However, further clarification is needed regarding whether adding water retaining agents, inhibitors, and straw can promote corn production in this semi-arid cropland. The cinnamon soil of western Liaoning was taken as the test object to explore the effects of water retaining agents, inhibitors, and corn stalks addition on corn yield, which provided scientific basis for rational utilization of corn stalks resources, promotion of high yield of corn and improvement of soil fertility. EXPERIMENTAL Field Site and Experimental Design The field experiment was conducted at the field experimental station of the Liaoning Key Laboratory of Water-Saving Agriculture in Fuxin County, northeast China. The annual average temperature is 7.2 °C, the annual average precipitation is about 480 mm, and the average sunshine time is about 2865 h. The rainfall situation in 2021 is shown in Fig. 1. The test soil was cinnamon soil with an organic matter content of 13.4 g kg-1, a total N of 1.0 g/kg, a total phosphate (P) of 0.4 g/kg, a total potassium (K) of 22.8 g/kg, an available P of 53.6 mg kg-1, and an exchangeable K of 86.7 mg kg-1. Soil bulk density (0 to 20 cm) was 1.51 g cm-3, and the pH (H2O) was 5.5. The field was set up in spring 2021. The farming system is continuous corn with one season per year. The split zone experiment design with three replicates was adopted, and the main division was divided into 3 treatments, which were natural rainfall (R), adding water retaining agent PAM (white small particle cationic polymer produced by Yunze Chemical Co., Ltd. for water retention), and adding water retaining agent potassium polyacrylate (K-PAA) (white small particle PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3639 polyacrylate water retaining agent produced by Hairuida Co., Ltd). The subdivision was divided into 5 treatments, namely no fertilization control (CK), conventional fertilization (U), conventional fertilization + corn stalks (US), conventional fertilization + inhibitors (UI), and conventional fertilization + inhibitors + corn stalks (UIS). The dosage of PAM and K-PAA was 30 kg hm-2. The conventional fertilizer used for fertilization were urea, superphosphate, and potassium chloride (KCl), and the application levels were N 156 kg ha-1, P 26 kg ha-1, and K 60 kg ha-1, respectively. The inhibitors were NBPT (N-(n- butyl)thiophosphoric triamide) and DMPP (3,4-dimethylpyrazole phosphate), applied at a dosage of 1% and 2% of urea N, respectively. Corn stalks were crushed (5 to 10 cm) and returned to the field (9.0 tons ha-1). All fertilizers were applied once during planting on May 10, 2021. The area of each plot was 40 m2 (5 m × 8 m). The planting density of the corn was 55,000 plants ha-1. The corn variety was “H188” spring maize (Zea mays L., a late maturing maize variety based on Food and Agriculture Organization of the United Nations (FAO) standards, with a 127 day growing period). Fertilizer was spread and rotary plowed to a depth of 15 to 20 cm before sowing. Plant protection and irrigation were not used. Weeds were pulled manually, and the corn was harvested manually. Fig. 1. Rainfall during the 2021 corn growing season Sample Collection and Analysis Three soil cores were randomly selected from each treatment plow layer (0 to 20 cm) during the corn seedling stage (June 16th), jointing stage (July 16th), filling stage (August 18th) and mature stage (September 24th). The soil samples were composited, sieved (2 mm), and stored at 4 °C until used for analysis. Soil moisture content was determined using the aluminum box drying method (105 °C). Soil moisture content is the percentage of water in the soil as a percentage of the weight of fresh soil. Soil ammonium nitrogen (NH4 +-N) and nitrate nitrogen (NO3 --N) were extracted with 2 M KCl solution (Meng et al. 2023), filtered, and analyzed with a continuous flow analyzer (AA3, Bran + Luebbe, PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3640 Norderstedt, Germany). Available P was extracted using 0.5 mol/L NaHCO3, and available K was extracted using neutral 1 mol/L ammonium acetate (NH4Oac) (Zhao et al. 2004). Soil organic carbon (SOC) and total N contents were determined by dry combustion of the samples using an Elemental Analyzer (Vario EL III, Hanau, Germany) (Yang et al. 2017). The corn yield was measured after air drying. Statistical Analysis All analyses were performed using Statistical Package for the Social Sciences (SPSS) Statistics 16.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) was used for testing the treatment effects with Duncan analysis. Significance was P < 0.05. Pearson correlation analysis was used for the correlation between corn yield and soil physicochemical properties. The response of corn yield to the application of water retaining agents, inhibitors, and corn stalks was analyzed using univariate analysis of variance. Tables and figures were prepared with Excel 2016 (Microsoft Corp., USA) and Origin 8 (Origin Lab Corp., USA), respectively. The data in the figures and tables are the average value ± standard error. RESULTS AND DISCUSSION Soil Moisture Content The variation range of soil moisture content in different corn growth periods was 13% to 18% (Table 1). The mature stage had the highest soil moisture content (17% to 18%), followed by jointing stage (16% to 18%), filling stage (15% to 16%), and seedling stage (13% to 17%). The treatments with the highest soil moisture content during the corn seedling stage were AUIS (17%), BUIS (17%), AUS (16%), RUS (16%), BUS (16%), and RUIS (16%), while the lowest treatment was RU (13%). There was no significant difference in soil moisture content among all treatments in other periods. Corn stalks returning was able to significantly reduce soil moisture loss in corn seedling stage (Table S1). Soil Ammonium Nitrogen The content of NH4 +-N in soil was the highest at the corn seedling stage, and then it decreased rapidly. The content of NH4 +-N remained stable at the corn filling stage and maturity stage (Table 2). The addition of water retaining agents, inhibitors and corn stalks significantly affected the soil NH4 +-N content in corn seedling stage, among which the application of PAM increased the soil NH4 +-N content, and the addition of inhibitors and corn stalks decreased the soil NH4 +-N content (Table S2). The addition of water retaining agents and inhibitors also significantly affected the soil NH4 +-N content at corn mature stage, in which the application of K-PAA increased the soil NH4 +-N content, and the addition of inhibitors decreased the soil NH4 +-N content (Table S2). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3641 Table 1. Soil Moisture Content in Topsoil at Different Growth Stages of Corn Treatments Seeding stage Jointing stage Filling stage Mature stage R CK 14% ± 0%bcC 17% ± 0%aA 16% ± 1%aB 18% ± 0%aA U 13% ± 0%cD 16% ± 0%aB 15% ± 0%aC 17% ± 0%aA US 16% ± 0%abBC 17% ± 0%aAB 15% ± 1%aC 18% ± 0%aA UI 14% ± 1%bcC 17% ± 0%aAB 15% ± 0%aBC 18% ± 0%aA UIS 16% ± 1%abcAB 17% ± 0%aA 15% ± 1%aB 18 ± 0%aA PAM CK 14% ± 1%bcC 17% ± 0%aA 16% ± 0%aB 18% ± 0%aA U 14% ± 1%bcB 17% ± 0%aA 15% ± 1%aAB 17% ± 1%aA US 16% ± 1%abA 17% ± 1%aA 15% ± 0%aA 17% ± 0%aA UI 14% ± 1%bcB 18% ± 1%aA 16% ± 1%aAB 18% ± 0%aA UIS 17% ± 1%aA 18% ± 1%aA 16% ± 1%aA 17% ± 1%aA K- PAA CK 14% ± 0%bcC 17% ± 1%aA 16% ± 0%aB 17% ± 0%aA U 14% ± 1%bcC 17% ± 0%aBC 15% ± 0%aAB 18% ± 1%aA US 16% ± 1%abcA 17% ± 1%aA 15% ± 1%aA 17% ± 0%aA UI 14% ± 1%bcB 17% ± 1%aA 16% ± 0%aAB 17% ± 1%aA UIS 17% ± 0%abB 17% ± 0%aA 16% ± 0%aC 18% ± 0%aA R: Natural rainfall, PAM: Polyacrylamide addition, K-PAA: Potassium polyacrylate addition, CK: control check with no fertilization, U: urea application, US: urea application + corn stalks returning, UI: urea application + inhibitors, UIS: urea application + inhibitors + corn stalks returning The lowercase letters in columns indicate significant differences between different treatments during the same period, while the uppercase letters indicate significant differences between different periods of the same treatment at P < 0.05 according to the Duncan’s test (n = 3), the same below Table 2. NH4 +-N (mg kg-1) in Topsoil at Different Growth Stages of Corn Treatments Seeding stage Jointing stage Filling stage Mature stage R CK 17.57 ± 0.13bcA 4.7 ± 0.25cB 2.67 ± 0.36aC 2.01 ± 0.19cC U 17.51 ± 0.6bcA 5.9 ± 0.2abcB 2.44 ± 0.06aC 2.85 ± 0.87bcC US 17.25 ± 0.83bcA 5.29 ± 0.4abcB 3.04 ± 0.63aC 3.76 ± 0.43abBC UI 17.08 ± 0.84bcA 6.04 ± 0.63abcB 2.97 ± 0.53aC 2.99 ± 0.15bcC UIS 15.54 ± 0.33bcA 5.32 ± 0.43abcB 2.82 ± 0.41aC 2.04 ± 0.15cC PAM CK 15.61 ± 0.49bcA 7.4 ± 0.83aB 2.67 ± 0.22aC 2.16 ± 0.4cC U 52.39 ± 1.49aA 4.72 ± 0cB 2.31 ± 0.32aB 3.83 ± 0.82abB US 12.94 ± 1.04bcA 5.96 ± 0.54abcB 2.69 ± 0.17aC 2.47 ± 0.34bcC UI 19.84 ± 4.59bA 5.13 ± 0.29bcB 2.66 ± 0.14aB 3.12 ± 0.14bcB UIS 17.04 ± 2.06bcA 5.96 ± 0.56abcB 3.16 ± 0.54aB 2.22 ± 0.09cB K-PAA CK 11.22 ± 3.01cA 5.56 ± 0.68abcB 2.68 ± 0.27aB 3.04 ± 0.56bcB U 14.84 ± 3.61bcA 5.2 ± 0.5bcB 2.91 ± 0.46aB 3.33 ± 0.6abcB US 18.6 ± 4.3bcA 6.53 ± 0.27abcB 3.01 ± 0.05aB 4.75 ± 0.22aB UI 12.96 ± 0.51bcA 6.39 ± 0.98abcB 2.54 ± 0.23aC 3.3 ± 0.5abcC UIS 12.22 ± 0.45cA 7.27 ± 1.46abB 2.48 ± 0.24aC 3.47 ± 0.11abcC Soil Nitrate Nitrogen The content of NO3 --N in soil was the highest at corn seedling stage, and then it decreased rapidly. The content of NO3 --N remained stable at corn mature stage (Table 3). The addition of water retaining agents significantly affected soil NO3 --N content at the seedling stage and jointing stage, and the addition of PAM significantly increased soil NO3 - PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3642 -N content. The application of inhibitors significantly reduced the soil NO3 --N content in the corn jointing stage (Table S3). Table 3. NO3 --N (mg kg-1) in Topsoil at Different Growth Stages of Corn. Treatments Seeding stage Jointing stage Filling stage Mature stage R CK 18.6 ± 3.02cdA 4.2 ± 1.18eB 3.77 ± 0.01cdB 2.24 ± 0.49abB U 16.51 ± 3.05cdA 8.51 ± 0.8bcB 5.19 ± 0.62abcB 2.68 ± 0.48abC US 17.12 ± 1.66cdA 5.35 ± 0.42eB 4.98 ± 0.61abcdB 2.57 ± 0.38abB UI 14.7 ± 3.24cdA 8.44 ± 0.62bcB 6.14 ± 0.71aBC 2.35 ± 0.14abC UIS 18.44 ± 0.02cdA 4.26 ± 0.6eB 3.67 ± 0.16cdB 1.73 ± 0.21bC PAM CK 9.17 ± 2.73dA 4.88 ± 0.7eAB 3.82 ± 0.2cdB 1.63 ± 0.22bB U 39.66 ± 3.91bA 6.37 ± 0.78cdeB 3.43±0.38dB 2.4 ± 0.19abB US 13.53 ± 3.03cdA 10.75 ± 0.24aA 4.86 ± 0.65abcdB 2.04 ± 0.32abB UI 19.45 ± 2.66cA 5.88 ± 0.38deB 5.18 ± 0.29abcB 2.22 ± 0.57abB UIS 48.33 ± 0.79aA 8.19 ± 1.23bcdB 5.79 ± 0.63abB 2.66 ± 0.28abC K-PAA CK 13.34 ± 3.85cdA 5.51 ± 0.22eB 3.71 ± 0.56cdB 1.85 ± 0.01bB U 14.81 ± 2.74cdA 5.99 ± 0.57deB 4.17 ± 0.51bcdB 2.14 ± 0.12abB US 18.64 ± 5.78cdA 9.73 ± 1.15abAB 4.49 ± 0.66abcdB 3.06 ± 0.59aB UI 11.73 ± 2.22cdA 7.88 ± 0.64bcdB 5.15 ± 0.2abcBC 2.5 ± 0.33abC UIS 12.01 ± 0.48cdA 1.95 ± 0.02fB 4.81 ± 0.46abcdC 2.1 ± 0.01abC Table 4. Available P (mg kg-1) in Topsoil at Different Growth Stages of Corn Treatments Seeding stage Jointing stage Filling stage Mature stage R CK 38.05 ± 3.68ghA 48.52 ± 8.32cdA 29.3 ± 1.28fA 41.84 ± 6.23defA U 73.36 ± 0.55aA 39.15 ± 2.24defC 58.43 ± 3.97aB 45.31 ± 4.82bcdeC US 67.27 ± 9.8abA 67.99 ± 0.51aA 30.87 ± 1.66fB 40.27 ± 4.62efB UI 53.45 ± 0.11cdeAB 47.69 ± 1.37cdeAB 44.15 ± 5.03deB 61.62 ± 7.14aA UI S 39.25 ± 0.2fghB 39 ± 1.88defB 48.11 ± 3.39bcdA 45.41 ± 1.03bcdeAB PAM CK 25.35 ± 1.64iC 36.85 ± 3.98efB 57.91 ± 0.54aA 29.22 ± 2.08fBC U 48.97 ± 4.8defgB 63.72 ± 1.56aA 46.34 ± 2.6cdeB 56.08 ± 4.66abcdAB US 65.56 ± 2.05abcA 52.63 ± 4.15bcBC 56.72 ± 0.59abB 46.62 ± 2.61bcdeC UI 44 ± 6.81efghA 42.44 ± 1.03cdefA 37.35 ± 3.03efA 39.38 ± 4.5efA UI S 50.05 ± 5.16defgAB 37.11 ± 2.68efB 45.44 ± 5.84cdeB 61.97 ± 3.54aA K- PAA CK 42.6 ± 4efghB 36.65 ± 1.79fB 41.36 ± 1.64deB 58.91 ± 3.69abA U 32.36 ± 0.24hiB 60 ± 1.95abA 58.39 ± 1.52aA 54.06 ± 5.56abcdeA US 52.04 ± 2.49defA 49.42 ± 0.91cdA 32.21 ± 1.28fB 43.13 ± 5.55cdefA UI 40.25 ± 0.96efghAB 43.19 ± 0.7cdefA 31.65 ± 2.39fB 38.85 ± 5.74efAB UI S 58.2 ± 2.75bcdA 32.75 ± 5.57fB 54.37 ± 1.74abcA 57.36 ± 2.3abcA PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3643 Soil Available Phosphorus The content of available P in soil changed little in different growing periods of corn (Table 4). The addition of water retaining agents, inhibitors, and corn stalks significantly affected the soil available P content in corn seedling stage, in which the application of corn stalks increased the soil available P content, and the addition of PAM, K-PAA, and inhibitors decreased the soil available P content. Only the addition of inhibitors reduced soil available P content in corn jointing stage (Table S4). Soil Exchangeable Potassium Soil exchangeable K content changed little during the growing period of corn (Table 5). Corn stalks addition significantly increased the exchangeable K content in corn seedling stage but decreased the exchangeable K content in corn mature stage. The addition of PAM significantly promoted the exchangeable K content in soil at corn mature stage (Table S5). Table 5. Exchangeable K (mg kg-1) in Topsoil at Different Growth Stages of Corn Treatments Seeding stage Jointing stage Filling stage Mature stage R CK 85.84 ± 12.2deA 86.06 ± 2.4abA 67.84 ± 4.49aA 79.77 ± 5.02bcA U 102.9 ± 12.63bcdA 87.91 ± 5.69abAB 67.58 ± 2.48aB 72.4 ± 2.58bcB US 101.65 ± 5.59bcdA 68.57 ± 3.26bB 67.54 ± 6.27aB 72.88 ± 3.06bcB UI 79.45 ± 4.74deA 71.89 ± 5bAB 64.01 ± 0.75aB 79.38 ± 2.96bcA UIS 104.66 ± 13.68bcdA 84.81 ± 14.11abAB 63.66 ± 5.28aB 76.84 ± 2.31bcAB PAM CK 67.62 ± 1.35eB 67.11 ± 1bB 64.14 ± 1.42aB 87.69 ± 7.72bA U 117.23 ± 6.86bcA 102.44 ± 17.34aAB 76.88 ± 9.34aB 111.68 ± 3.06aAB US 86.03 ± 6deA 71.69 ± 2.12bAB 63.56 ± 0.86aB 85.54 ± 11.22bA UI 90.23 ± 13.91cdeA 70.86 ± 8.7bA 70.98 ± 5.74aA 74.47 ± 4.01bcA UIS 126.41 ± 13.65abA 82.61 ± 6.34abB 71.59 ± 3.7aB 78.77 ± 5.15bcB K- PAA CK 79.04 ± 4.95deA 73.09 ± 10.6abA 64.65 ± 4.22aA 73.7 ± 4.14bcA U 80.03 ± 0.2deA 75.68 ± 11.19abA 75.76 ± 3.51aA 76.11 ± 3.97bcA US 148.05 ± 5.63aA 70.64 ± 14.07bB 67.75 ± 4.4aB 68.96 ± 2.18cB UI 86.14 ± 6.35deA 77.31 ± 5.77abA 69.69 ± 4.25aA 76.97 ± 2.43bcA UIS 86.7 ± 6.1deA 75.85 ± 6.12abA 72.79 ± 0.3aA 73.56 ± 2.69bcA Soil Organic Carbon and Total Nitrogen As shown in Fig. 2A, the SOC content was about 8.5 g kg-1, and there was no significant difference in all treatments except that AU treatment was significantly higher than RUIS and AUI treatments. The total N content of soil was about 0.9 g kg-1, and there was no significant difference among all treatments (Fig. 2B). The addition of water retaining agents, inhibitors, and corn stalks had no significant effect on SOC and total N (Table S6). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3644 Fig. 2. Effects of water retaining agents and inhibitors application and corn stalks returning on SOC (A) and total N (B). R: natural rainfall, PAM: polyacrylamide addition, K-PAA: potassium polyacrylate addition, CK: control check with no fertilization, U: urea application, US: urea application + corn stalks returning, UI: urea application + inhibitors, UIS: urea application + inhibitors + corn stalks returning. Different letters indicate significant difference at P < 0.05. The same considerations apply to subsequent figures Fig. 3. Effects of water retaining agents and inhibitors application and corn stalks returning on corn yield Corn Yield The corn yield ranged from 11,400 to 14,200 kg hm-2. The PAMUI treatment had the highest corn yield, significantly higher than K-PAACK, K-PAAUIS, RU, RUS, PAMUS, PAMCK and RCK treatments, but not significantly different from PAMU, RUIS, K-PAAU, RUI, PAMUIS, K-PAAUS and K-PAAUI treatments. The RCK treatment had the lowest corn yield, but was not significantly different from treatment PAMUIS, K- PAAUS, K-PAAUI, K-PAACK, K-PAAUIS, RU, RUS, PAMUS and PAMCK treatments (Fig. 3). Water retaining agents addition had no significant effect on corn yield, while inhibitors addition increased corn yield and corn stalks returning decreased corn yield (Table S6, P < 0.1). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3645 Pearson Correlation Analysis of Corn Yield and Soil Physicochemical Properties Through Pearson correlation analysis, it was found that there was no significant correlation between corn yield and other soil physicochemical properties except soil moisture content at filling stage (Table 6). There was a significant negative correlation between corn yield and soil moisture content at filling stage. Table 6. Pearson Correlation Analysis of Corn Yield with Soil Moisture Content, NH4 +-N, NO3 --N, Available P, and Exchangeable K Soil moisture content NH4 +-N NO3 --N Available P Exchangeable K Corn yield Seeding stage -0.163 0.276 0.152 -0.064 0.154 Jointing stage -0.234 -0.049 0.050 -0.017 -0.054 Filling stage -0.391** -0.133 0.171 -0.042 -0.047 Mature stage -0.087 0.256 0.067 0.176 0.075 The values in the table are Pearson correlation coefficients (n = 3), **The correlation is significant at P < 0.01 Effects of Water Retaining Agents, Inhibitors and Corn Stalks Addition on Soil Physicochemical Properties and Corn Yield The corn yield is known to be influenced by the soil physicochemical properties and climate. Fertile soil and suitable climate are conducive to high yield of corn (Zhang et al. 2020b; Zhao et al. 2023). The addition of water retaining agents, inhibitors, and corn stalks can affect soil physicochemical properties. Polyacrylamide addition increased the content of NH4 +-N (38.7%, Table 2 and Table S2) and NO3 --N (52.4%, Table 3 and Table S3) in seedling stage, and the content of exchangeable K (14.9%, Table 5 and Table S5) in mature stage, but decreased the content of available P (13.8%, Table 4 and Table S4) in seedling stage. Potassium polyacrylate addition increased the content of NH4 +-N (31.1%, Table 2 and Table S2) in mature stage and decreased the content of available P (16.9%, Table 4 and Table S4) in seedling stage (Table S2, S4). This may be due to the fact that PAM contains ammonium ion, which directly increases soil inorganic N, and polyacrylates water retaining agents have the characteristics of slow release of water, which stimulates the growth of soil microorganisms and urease activity (Zhang et al. 2020a). In addition, the water retaining agents generally contain micropores. These can allow some small molecules or ions to diffuse into the water retaining agents’ molecules and be wrapped by the agents in their water-swollen condition. Alternatively, the nutrients can be temporarily fixed by cation exchange and adsorption within the agents (Li et al. 2014), resulting in the reduction of available P. The effect of PAM on exchangeable K and K-PAA on NH4 +-N may be caused by the competition between NH4 +-N and potassium ions on the 2:1 clay mineral interlayers (Scherer et al. 2014). Addition of inhibitors decreased the contents of NH4 +-N (29.1%, Table 2 and Table S2) and available P (16.0%, Table 4 and Table S4) in the corn seedling stage, NO3 --N (21.63%, Table 3 and Table S3) and available P (27.2%, Table 4 and Table S4) in the jointing stage, and NH4 +-N (18.3%, Table 2 and Table S2) in the mature stage. The effect of inhibitors on inorganic N content may be mainly through the inhibition of urease activity by NBPT to delay the conversion of urea to NH4 +-N. In addition, DMPP inhibits the conversion of NH4 +-N to NO3 --N and reduces the production PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3646 and accumulation of nitrate (Rose et al. 2018; Cui et al. 2022). The effect of inhibitors on the content of available P may be due to inhibitors’ application increasing the effective duration of inorganic N in soil and promoting the assimilation ability of crops to N and P (Cui et al. 2022). Corn stalks returning could increase soil moisture (18.1%, Table 1 and Table S1), reduce the content of NH4 +-N (30.5%, Table 2 and Table S2) at seedling stage and exchangeable K (7.02%, Table 5 and Table S5) at the mature stage, and increase the content of available P (13.67%, Table 4 and Table S4) and exchangeable K (17.54%, Table 5 and Table S5) at the seedling stage. The effect of corn stalks addition on soil moisture may be due to: 1) reducing the evaporation loss of soil water; 2) increased soil porosity and improved soil water holding capacity; and 3) the corn stalks contains more pores that can absorb water (Zhang et al. 2020b; Thíebeau et al. 2021). Corn stalks have a high C to N ratio (54.6:1), which can accelerate microbial growth and improve N absorption, possibly leading to a decrease in NH4 +-N (Chen et al. 2014). In addition, corn stalks also contain a large amount of nutrients, which may be the reason for the increase in available P and exchangeable K content in the soil (Liu et al. 2011). Soil organic matter content is an important index to measure soil fertility (Bai et al. 2016). The study found that the addition of water retaining agents, inhibitors, and corn stalks had no significant effect on SOC and total N, but the combination of inhibitors and corn stalks significantly promoted the increase of SOC (Table S6). This may be due to the application of inhibitors increasing the effective duration of inorganic N in the soil (Cui et al. 2022), alleviating N scarcity caused by high C input (corn stalks addition) and promoting the fixation effect of microorganisms on corn stalks charcoal (Chen et al. 2014; Cheng et al. 2017). The addition of water retaining agents had no significant effect on corn yield (Table S6), which was consistent with Holt et al. (2023). This is likely due to a 36% increase in rainfall during the growing season (Fig.1, 655 mm), reducing water stress on corn growth. Inhibitors addition increased corn yield (Table S6, P < 0.1). Previous studies have also found that inhibitors application can have a good yield increase effect, especially the combination of urease inhibitor and nitrification inhibitor, through the regulation of fertilizer N conversion to achieve yield increase (Shi et al. 2015; Wu et al. 2019; Qi et al. 2022 ). The addition of corn stalk is considered to be conducive to the increase of corn yield (Qin et al. 2021; Wang et al. 2021), but the corn yield did not increase in the study (Table S6), which may be due to the fact that it may take a long time for corn stalk addition to show a positive effect on corn yield (Chang et al. 2020; Yang et al. 2020; Islam et al. 2022). Therefore, according to research results, the combination of inhibitors and corn stalks application can increase soil fertility and has the potential to increase corn yield, which is the best fertilization mode in this area. Whether water retaining agents are conducive to increasing corn yield needs to be verified in drought years. CONCLUSIONS 1. Addition of the water retaining agent polyacrylamide (PAM) increased the content of NH4 +-N and NO3 --N in seedling stage, and the content of exchangeable K in mature stage, but it decreased the content of available P in the seedling stage. Addition of the potassium salt of polyacrylate (K-PAA) as a water retaining agent increased the content of NH4 +-N and decreased the content of available P in the corn seedling stage. Inhibitors addition decreased the contents of NH4 +-N and available P in the seedling stage, NO3 -- N and available P in the jointing stage and NH4 +-N in the mature stage. Returning corn PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3647 stalks to the soil could maintain soil moisture, reduce the content of NH4 +-N at the seedling stage and exchangeable K at the mature stage, and increase the content of available P and exchangeable K at the seedling stage. 2. The addition of water retaining agents (PAM and K-PAA) had no significant effect on corn yield. Combined application of inhibitors and corn stalks can increase SOC and ensure corn yield, which is the best fertilization mode in semi-arid cropland. ACKNOWLEDGMENTS This work was supported by the Shandong Province key research and development plan project (2022SFGC0301), the National Key Research and Development Program of China (2022YFD170060503; 2022YFD170060107; 2022YFD1500604), the National Scientific Foundation Project of China (32272232), the High Level Innovation Team of Xingliao Talent Plan (XLYC2008019), the Liaoning “Take the Lead” Project (2023JH1/10400017), the Natural Science Foundation from Science and Technology Department of Liaoning Province (2022-BS-023), the Applied Basic Research Program of Liaoning Province (2023JH2/101600048) and the Technical Mission of black soil conservation in Fuxin Mongolia Autonomous Country, Liaoning Province (1685524420083). REFERENCES CITED Bai, S. B., Pei, J. B., Li, S. Y., An, T. T., Wang, J. K., Meng, F. K., and Xu, P. 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Soil Moisture Content in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Seeding stage Jointing stage Filling stage Mature stage Water retaining agent (W) 0.605 0.310 0.688 0.863 Inhibitors (I) 0.383 0.053 0.153 0.718 Corn stalks (S) 0.000*** 0.423 0.921 0.742 WI 0.931 0.714 0.797 0.801 WS 0.809 0.836 0.864 0.457 IS 0.749 0.902 0.917 0.856 WIS 0.738 0.931 0.987 0.198 The values in the table are P values (n = 3). *The correlation is significant at P<0.05, **The correlation is significant at P<0.01, ***The correlation is significant at P<0.001, the same below. Table S2. NH4 +-N in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Seeding stage Jointing stage Filling stage Mature stage Water retaining agent (W) 0.000*** 0.129 0.901 0.028* Inhibitors (I) 0.000*** 0.267 0.863 0.022* Corn stalks (S) 0.000*** 0.194 0.294 0.642 WI 0.001** 0.576 0.256 0.890 WS 0.000*** 0.107 0.725 0.021* IS 0.001** 0.662 0.549 0.105 WIS 0.000*** 0.980 0.693 0.194 Table S3. NO3 --N in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Seeding stage Jointing stage Filling stage Mature stage Water retaining agent (W) 0.000*** 0.021* 0.659 0.852 Inhibitors (I) 0.666 0.000*** 0.057 0.278 Corn stalks (S) 0.275 0.256 0.727 0.915 WI 0.022* 0.076 0.139 0.266 WS 0.978 0.000*** 0.014* 0.449 IS 0.000*** 0.000*** 0.050 0.398 WIS 0.000*** 0.000*** 0.497 0.114 Table S4. Available P in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Seeding stage Jointing stage Filling stage Mature stage Water retaining agent (W) 0.001** 0.304 0.590 0.628 Inhibitors (I) 0.001** 0.000*** 0.056 0.246 Corn stalks (S) 0.011* 0.057 0.437 0.973 WI 0.000*** 0.069 0.044* 0.160 WS 0.000*** 0.000*** 0.000*** 0.033* IS 0.174 0.001** 0.000*** 0.005** WIS 0.748 0.000*** 0.000*** 0.004** PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Wu et al. (2024). “Corn yield & semi-arid cropland,” BioResources 19(2), 3637-3652. 3652 Table S5. Exchangeable K in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Seeding stage Jointing stage Filling stage Mature stage Water retaining agent (W) 0.476 0.585 0.179 0.000*** Inhibitors (I) 0.057 0.683 0.696 0.089 Corn stalks (S) 0.005** 0.342 0.273 0.036* WI 0.042* 0.572 0.761 0.000*** WS 0.055 0.865 0.642 0.313 IS 0.406 0.026* 0.137 0.056 WIS 0.000*** 0.340 0.526 0.035* Table S6. Organic C, Total N, and Corn Yield in Response to Water Retaining Agents, Inhibitors, and Corn Stalks Returning Factors Organic C Total N Corn yield Water retaining agent (W) 0.259 0.510 0.366 Inhibitors (I) 0.756 1.000 0.086 Corn stalks (S) 0.705 0.672 0.086 WI 0.237 0.818 0.129 WS 0.399 0.694 0.127 IS 0.022* 0.549 0.757 WIS 0.114 0.583 0.990