Optimizing Nitrogen Fertilizer Quantities in Cereal Crop Root Systems to Minimize Leaching

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Loss of nitrogen due to leaching is one of the most pressing issues in agriculture as it leads to excessive crop production costs and pollution. N leaching contributes to atmospheric and aquatic pollution [1]. The production of nitrogen fertilizers accounts for 3% of worldwide natural gas consumption and contributes to 3% of global greenhouse gas emissions. Fertilizer leaching accounts for 23 trillion grams of nitrogen loss per year [2]. Understanding resource capture in cereal root systems provides yield and production data useful for environmental and economic efficiency. Thus, there is already considerable research on modeling water and N uptake by root systems. There are general models that describe uptake with root length density over the course of a season [3]. There are also a variety of existing models used to simulate mineral movement in soil systems that have been adapted to model N leaching in crop root systems, including DRAINMOD, DSSAT, N_ABLE, and EPIC [4]. We aim to model the consumption of nitrogen by cereal crop roots, as well as leaching under topsoil fertilizer placement in order to optimize the amount of fertilizer needed. An optimized amount of fertilizer will maximize plant uptake while minimizing the amount leached in the soil. It will save farmers money while minimizing ecological impact. We will model the nitrogen distribution and absorption over a set amount of time. During this length of time, rainfall will occur at certain periods in order to mimic real environmental conditions. In order to accurately model the top-down system, we must first simulate the uptake of the fertilizer into the water during rainfall. We model our system as 2D axisymmetric. We will describe our system using mass transfer equations representing the convective flow, transient uptake and dispersion over time under known initial concentrations and dispersive constants. We then use fluid flow equations to model the traversal of water through the soil/root system. The absorption of the water and N by the plant is a function of the root density, for which the equations are known. Using this information in simulation, we will be able to model how much nitrogen is absorbed by the root system as well as how much is leached beyond the boundaries of the crop. We found that most root uptake of nitrogen occurs in the top-most region which was expected. N uptake also increases as root length density increases. We plotted total N flow and uptake against time and found that only 30.3% of initial nitrogen was absorbed by the plant over the course of 90 days. Additionally, our water content and matric potential are validated using a study by Wu et. al. in which matric potential, h, and water content, θ, were measured 5 days after an irrigation event [5]. We modeled our precipitation to match their field conditions. We plotted our matric potential with respect to depth into the soil layer and our water content with respect to depth against the Wu et. al. results. The trend of our model matches that of the measured values with reasonable precision. Our matric potential with respect to depth plot rendered an R2 value of 0.766 and our plot of water content with respect to depth achieved an R2 of 0.937 (Fig. 12 & 13).
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fertilizer, absorption, nitrogen, cereal crop, leaching
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