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Effect of Variable Rate Irrigation and Nitrogen Fertilizer Rates on Crop Productivity and Water Quality

Start Date: 2020
Principal Investigator: Vasudha Sharma, Yuxin Miao and Fabian Fernandez
Organization: University of Minnesota, Department of Soil, Water, and Climate
Status: Ongoing

Background Info

In Minnesota, the interest in deficit/limited and variable rate irrigation management, to address/reduce water quality and quantity problems, has been increasing amongst farmers, agricultural professionals and key stakeholders. However, it’s challenging to understand, how much reduction in irrigation rate as compared to full irrigation and what amount of nitrogen (N) fertilizer is optimum, under that reduced irrigation rate, for sustainable crop production. Consequently, when farmers use deficit irrigation amounts in combination with recommended N rates that are developed under well-watered conditions, plants cannot utilize all the N applied and thus the remaining can be lost in the environment.

Water quality and quantity issues in irrigated regions of the state have led to scrutiny of groundwater by the government, leading to the development of new regulatory approaches and groundwater policies. One such regulation is the Groundwater Protection Rule developed by the Minnesota Department of Agriculture (MDA) that would regulate the N fertilizer use in the areas that are vulnerable to groundwater contamination. Such rules are important in order to reduce the impact of agriculture on the environment but at the same time, requires robust and evolving research based scientific knowledge, specifically in the fields like irrigation that has not been explored much in Minnesota. An innovative research, that integrates N fertilizer and irrigation or crop water use, needs to be developed to back up these programs and rules with scientific research based knowledge and also help growers in efficient farm management.

Several researches have investigated the combined effect of irrigation and N on crop production, nitrate leaching and water use efficiency, and found that N and water are codependent management factors that cannot be evaluated independently (Al-Kaisi and Yin, 2003; Pandey et al., 2000a; Pang et al. 1997). In these studies researchers found that crop water productivity (yield/water use) vary with varying rates of N and irrigation and that under deficit irrigation, N must be correspondingly adjusted to optimize economic crop production. However, most of this knowledge is based on research conducted in more arid regions where precipitation and the water balance of cropping systems are substantially different from those in Minnesota. To the best of our knowledge, very limited research has been done to investigate the N and irrigation interaction effect on nitrate leaching in corn cropping systems in Minnesota. One such research is Maharjan et al. (2014) who compared the effects of different N treatments for fully irrigated and minimum-irrigated corn in Becker, MN. They found greater yield-based nitrate leaching and lower grain yields in minimum-irrigated plots than fully irrigated plots. However, in their study, they used only one N rate (180 kg N/ha) under two irrigation levels with different types and timing of N fertilization.

Our overarching goal is to build capacity to provide government agencies, stakeholders and producers with scientific research-based irrigation and N management data, and information on fundamental relationships that help develop policy/rules, make better on-farm management decisions, and help advancing the sensor-based (proximal and remote sensing) irrigation and N management research. Since corn is one of the principle crops irrigated in Minnesota, our research will focus on continuous-corn cropping systems under sprinkler irrigation.


  1. Evaluate variable irrigation and N rate interaction effects on corn yield, nitrate-N leaching, crop evapotranspiration, crop water productivity, and water- and N-use efficiency
  2. Develop corn evapotranspiration crop coefficient (Kc) curves for efficient irrigation management
  3. Develop proximal and UAV remote sensing-based non-destructive in-season corn water and N status diagnosis methods and in-season variable rate N and irrigation management strategies

Key Findings

Greater grain yield response existed at Becker than at Westport in 2020. This could be due to higher growing season temperature and lower rainfall at Becker than at Westport.

The maximum grain yield result obtained at SPRF was 220 bu/ac under the 75% irrigation and 280 lb N/ac treatment.

The lowest grain yield was also observed under 75% irrigated condition, however, it occurred at the lowest N treatment (0lb N/ac).

At all irrigation levels, no difference in grain yield was observed between 280 lb N/ac and 350 lb N/ac.

At Becker, there was no significant grain yield difference between 50%, 75% and 100% irrigation at any level of N application which suggests that limited irrigation can be effectively used to conserve water with minimal to no effect on grain yield.

With an increase in 20 lb N/ac in 75% irrigation treatment as compared to 100% irrigation, the yield increase was only 1 bu/ac which indicates that 100% irrigation is more economically efficient system.

At both sites, higher N rates (210 to 350 lb N/ac) had greater N leaching at all irrigation levels.

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