#The authors have contributed equally, should be considered as 1st authors
The increasing world population has forced excessive chemical fertilizer and irrigation to complete the global food demand, deteriorating the water quality and nutrient losses. Short-term studies do not compile the evidences; therefore, the study aimed to identify the effectiveness of reduced doses of inorganic fertilizer and water-saving practices, hence, a six-year experiment (2015–2020) was conducted in China to address the knowledge gap. The experimental treatments were: farmer accustomed fertilization used as control (525:180:30 kg NPK ha−1), fertilizer decrement (450:150:15 kg NPK ha−1), fertilizer decrement + water-saving irrigation (450:150:15 kg NPK ha−1), application of organic and inorganic fertilizer + water-saving irrigation (375:120:0 kg NPK ha−1 + 4.5 tones organic fertilizer ha−1), and application of controlled-release fertilizer (80:120:15 kg NPK ha−1). Each treatment was replicated thrice following a randomized complete block design. The results achieved herein showed that control has the highest losses in the six-year study for total nitrogen (225.97 mg L−1), total soluble nitrogen (121.58 mg L−1), nitrate nitrogen (0.93 mg L−1), total phosphorus (0.57 mg L−1), and total soluble phosphorus (0.57 mg L−1) respectively. Reduced fertilizer and water application improved crop nutrient uptake, nitrogen concentration was significantly enhanced with organic and inorganic fertilizer + water-saving irrigation, P concentration was increased with fertilizer decrement + water-saving irrigation, and K concentration was improved with fertilizer decrement + water-saving irrigation. Hence, this study concludes that reduced inorganic fertilizer dose combined with water-saving practices is significantly helpful in reducing nutrient leaching losses and improving nutrient uptake and water pollution. Further studies are needed to explore the impacts of reduced fertilization and water-saving irrigation on leaching losses. The benefits at different climatic conditions, soil types, and fertilizer types with application methods are also a research gap.
The world population is estimated to increase by 1.7 billion between now and 2050, giving rise to food and water security challenges [
Large portions of agrochemicals find their fate at the surface and in groundwater, resulting in poor global water quality and aquatic system deterioration [
In this scenario, the improvement in fertilization and irrigation management practices needs to be adopted to reduce the entry of N into surface and groundwater [
The lack of consecutive year-round investigations on N leaching at the field scale is the key factor for the current divergent study to reduce the water application in the agroecosystem. The scientific question considered was to assess how the reduced fertilization will affect losses under water saving conditions in the long-term. We consequently conducted a six-year field experiment in the Yellow River Irrigation Region of Ningxia Plain, China. The objectives of the study are to: (i) examine the nutrient leaching losses at three stages of corn (jointing stage, big trumpet stage, and after harvest) throughout the cropping season, (ii) study the leaching flux dynamics of N, and P during the investigation period, and (iii) propose suitable fertilization and irrigation practices to minimize nutrient leaching losses and improve nutrients uptake. The study has some limitations depending on the soil and fertilizer type, climatic zones, and use of organic fertilizer type.
A six-year-long field experiment was performed at Nongfeng village (42.32°N, 106.65°E) Wanghong, District Yongning, Ningxia, China. The area is located at an altitude of 1108 m and in arid to semi-arid plains. With the aims mentioned above, corn (
Keeping the local conditions in view, five treatments were applied in three replicates following a randomized complete block design (RCBD). The plot size was maintained at 8 m × 6 m (length x width), and corn seeds were sown. The treatments were: farmer accustomed fertilization (CON, 525:180:30 kg NPK ha−1) as control, fertilizer decrement (KF: 450:150:15 kg NPK ha−1), fertilizer decrement + water-saving irrigation (BMP1, 450:150:15 kg NPK ha−1), application of organic and inorganic fertilizer + water-saving irrigation (BMP2, 375:120:0 kg NPK ha−1 + 4.5 tones organic fertilizer ha−1 as commercial chicken manure), and application of controlled-release fertilizer (BMP3, 180:120:15 kg NPK ha−1). The treatments received the fertilizers in the form of urea (CH4N2O; 46% N), triple superphosphate (46% P2O5), potassium sulfate (50% K2O), and controlled-release fertilizer is coated urea (total nutrient ≥42%). Details for types of fertilizers, sources, composition, and application time are given in the supplementary file (Table S1).
Organic fertilizer, P, K, and controlled-release fertilizer were all applied in the base (ploughing after spreading), and N fertilizer was applied in the base of 60%. Topdressing was divided into two times, the first time at 20% (strip application) and the second time at 20% (spreading). Conventional irrigation treatments (CON, KF, and BMP3) received about 1300 m3 ha−1 irrigation volume each time. The volume of water in water-saving irrigation treatment (BMP1, BMP2) was 910 m3 ha−1 each time. The irrigation volume for winter irrigation was 1,800 m3 ha−1. In 2017, due to drought, the crop was irrigated 4 times (thrice in the corn growth period and once in winter). The irrigation volume of the first conventional irrigation treatment was 1,050 m3 ha−1, while for water-saving irrigation treatment, water volume was maintained at 735 m3 ha−1 every time. Whereas, the irrigation volume of the second, third, and winter irrigation was the same as that of 2016 and 2018. Irrigation volume was measured by the water meter. Details for corn planting, harvest, fertilization, irrigation date, and leaching time are given in the supplementary file (Table S2).
Corn (cv.
Lysimeter was used to collect the water leachate samples. The soil column in the lysimeter was 160 cm in length, 80 cm in height, and 60 cm in width. The soil inside the lysimeter was separated by plastic cloth, and a leaching barrel (40 cm in diameter and 35 cm in height) was placed beneath the lysimeter. The lid for the leaching barrel was covered with two layers of 80 mesh nylon and 3 cm thick quartz sand. When the leachate reaches at a depth of 80 cm, the leachate in the upper soil enters the leaching barrel due to gravity. In the leaching barrel, a connecting tube was inserted into the soil surface to allow the leachate to be pumped out with a vacuum pump and provide the leaching barrel for cleaning [
The leaching water (LW) samples were collected to analyze nutrient concentration. LW samples were collected at different plant growth stages, including the jointing stage (JS), big trumpet stage (BTS), and after harvest (AT; also known as winter irrigation). To minimize the standard error, three LW samples were collected and analyzed for TN, total soluble N (TSN), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), total P (TP), and total soluble P (TSP). TN was measured by the potassium persulfate-UV-VIS spectrophotometer (UV-1780, SHIMADZU, China), TSN, NH4+-N, and NO3−-N were analyzed by the continuous-flow analyzer (AA3, BRAN + LUEBBE, Germany) [
To determine the nutrient concentration in corn straw and grain, the samples from each plot were collected, dried, ground, and the homogenized mixture was digested and filtered. TN, TP, and TK concentrations were measured using Kjeldahl N determination (FOSS-USA), continuous flow analyzer (AA3-Germany), and inductively coupled plasma mass spectrometry (ICP-MS; Thermoscientific-USA), respectively [
The following formula was used to measure the nutrient (TN, TSN, NO3−-N, NH4+-N, TP, and TSP) leaching flux:
where F is nutrient leaching flux kg ha−1, n is times of farmland leaching production (underground leaching) in the monitoring period, Vi is water volume of the ith leaching, Ci nutrient concentration of the ith leaching (mg L−1), and S is the area of monitoring unit (m2).
Statistix software 8.1® was used to compare the means and significance of treatments (
Water analysis demonstrated that using reduced fertilizer and water-saving techniques minimizes the loss of nutrients through water leaching. At JS, CON showed the highest TN losses in 2015, 2016, 2018, and 2019. While KF and BMP2 resulted in the highest TN losses in 2017 and 2020. The treatment-wise trend line indicated that CON and KF had the highest TN losses in 2017. However, the losses were reduced in 2015 and KF in 2018, respectively. BMP1 showed the highest losses in 2020, significantly reducing the TN losses in 2018. Moreover, BMP2 significantly increased the losses in 2017, followed by 2020 and 2016. BMP3 also enhanced the losses in 2017 compared to other years (
Results revealed that TSN was also influenced by using the reduced fertilizer technique. At JS, CON increased the TSN losses in 2016, 2018, and 2019. However, KF indicated the highest TSN losses in 2015, 2017, and 2020 respectively. Whereas, the trend line showed that CON increased the TSN losses in 2017, followed by 2016. KF also improved the losses in 2017, followed by 2020, and BMP showed the highest losses in 2020. BMP2 and BMP3 significantly increased the TSN losses in 2017. Whereas, BMP1 increased the TSN losses in 2020 at JS, respectively (
At JS, CON and KF contributed equally to the highest NO3-N losses in 2015. While BMP1 showed the highest losses in 2016, BMP3 in 2017, CON in 2018 and 2019, and BMP2 in 2020. The trend line indicates that CON significantly increased its losses in 2019, followed by 2020. KF also reported the highest losses in 2020, followed by 2015. BMP1 increased the losses in 2020. BMP2 significantly reduced the losses in 2017. Moreover, BMP3 reported the highest losses in 2020, respectively (
Our results revealed that respective treatments also influenced NH4-N losses. At JS, BMP2 showed the highest NH4-N losses in 2015, CON in 2016, 2017, and 2020, BMP1 in 2018, and BMP3 in 2019. The trend line indicates that CON reported the highest losses in 2017, followed by 2020, KF in 2020 followed by 2017, BMP1 in 2017 followed by 2018, and BMP3 in 2019, followed by 2017. In addition, BMP2 significantly reduced the losses in 2017 (
Results showed that TP losses were highest with BMP2 in 2015 and 2016, CON in 2017, KF in 2018, BMP3 in 2019, and CON in 2020. All the treatments significantly enhanced the losses in 2017 except BMP3, which showed the highest value in 2019 (
At JS, minute TSP losses were observed during 2015–2017. Afterward, CON showed the highest losses in 2018 and 2019 and BMP3 in 2020. The trend line showed that CON increased the losses in 2019, KF in 2020, BMP1 in 2020, BMP2 in 2018–2020, and BMP3 in 2020, respectively (
The interaction effect of year*treatment was significant (
The interaction effect of year*treatment was significant (
The N concentration in grain was improved by BMP3 (2015) followed by BMP2 (2015) with respect to others. The value of grain N concentration (2.79%) of treatment BMP3 in 2015 remained the most prominent among all treatments. In 2018, BMP2 significantly reduced the grain N concentration compared to other treatments (
In 2017, treatment KF showed a 67.76% increase in grain yield over the KF treatment of 2015. In 2017, treatment BMP1 showed 47.95% better grain yield than the BMP1 treatment of 2015. Grain yield was enhanced with the application of BMP2 in 2015 (34.5%), 2016 (50.1%), 2018 (59.8%), 2019 (78.1%), and 2020 (45.5%) as compared to respective CON treatments. KF improved the grain yield in 2017 by up to 105.6% over the respective CON treatment (
The results achieved herein indicated that leaching flux was significantly affected (year*treatment) with the time and management of fertilization and irrigation practices (
The principal components analysis (PCA) determined the association among all the studied variables (
Ningxia province, located in North China, is receiving major consideration for agricultural production, especially corn and vegetables, in the zone of the Yellow River. The area is suitable for highly productive crops, which require higher inputs of chemical fertilizers and heavy irrigation [
The current study observed that N losses were significantly enhanced with chemical fertilization (
It was also observed that the loss amount of NO3−-N was higher than NH4+-N (
Rapid release of nutrients is an important factor contributing to agricultural nonpoint pollution, as observed in the CON treatment of the current study. Chemical fertilizers have high loss risks due to fast nutrient release. The results demonstrated that N and P losses were increased in the CON treatment compared to KF, BMP1, BMP2, and BMP3 throughout the six-year experiment. The nutrient uptake in straw and grains was significantly enhanced in all treatments compared to CON, ultimately increasing grain yield (
The techniques to reduce the N and P losses are divided into two categories: (i) in-field management and (ii) edge-of-field management. The in-field effectively reduces the nonpoint pollution load at the source point, including optimized cropping, reduced water use, and conservation tillage. Crop optimization can effectively enhance nutrient use efficiency and uptake [
The results achieved herein speculated that excessive, higher dose and continuous application of inorganic fertilizers results in higher N losses (
Reducing fertilizer rates with water-saving techniques is an effective practice for corn cultivation in the Yellow River Irrigation Region of Ningxia Plain, China. The results concluded that TN, TSN, NO3-N, NH4-N, TP, and TSP leaching losses were generally reduced with the combined use of organic and inorganic fertilizers and controlled irrigation. It is also an innovative approach to reducing water pollution and water safety. Moreover, it also improved nutrient concentration in straw and grain. Farmers can adopt such techniques to minimize fertilization costs, save water, and limit leaching losses. Further studies are needed to explore the impacts of reduced fertilization and water-saving irrigation on leaching losses. In addition, benefits at different climatic conditions, soil types, fertilizer types, and application methods can also be addressed.
This study received funds from the
The authors confirm their contribution to the paper as follows: study conception and design: Xiaotong Liu, Muhammad Amjad Bashir, Yucong Geng, Xuejun Zhang, and Hongbin Liu; data collection: Xiaotong Liu, Muhammad Amjad Bashir, Qurat-Ul-Ain Raza, Xuejun Zhang, Jianhang Luo, and Ying Zhao; analysis and interpretation of results: Xiaotong Liu, Muhammad Amjad Bashir, Qurat-Ul-Ain Raza, Ying Zhao, Muhammad Aon, and Abdur Rehim; draft manuscript preparation: Xiaotong Liu, Xuejun Zhang, Muhammad Amjad Bashir, Qurat-Ul-Ain Raza, Jianhang Luo, and Hongbin Liu. All authors reviewed the results and approved the final version of the manuscript.
The authors have no relevant financial or non-financial interests to disclose.