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The movement, transfer, and distribution of mobile nutrients such as potassium and nitrate, along with the less mobile phosphorus, are critical issues in soil chemistry, fertility, physics, and pollution at regional, local, and national levels. These factors are influenced by various elements, including irrigation, precipitation, fertilization, and agricultural practices. Although significant research has been conducted on drip irrigation in recent years, studies specifically focusing on the movement and distribution of potassium, phosphorus, and nitrate in drip irrigation systems—particularly their uptake by strategic crops like potatoes and maize—remain limited. The vertical and horizontal distribution of these nutrients is often uneven across most soil types and is particularly pronounced in drip irrigation systems. Thus, a comprehensive assessment and precise estimation of nutrient concentration, movement, distribution, and plant uptake require sophisticated field measurements and simulations using advanced plant-hydrological models. Integrating these approaches enhances resource efficiency, optimizes nutrient distribution, and ultimately improves crop yield. This study aimed to evaluate nutrient dynamics in potato and maize cultivation under a drip irrigation system at the Soil and Water Research Institute. Planting, maintenance, and harvesting operations for maize and potatoes were carried out with specific fertilizer treatments, along with soil and plant sampling at the research farm utilizing the drip irrigation system. The goal was to maintain all standard agricultural operations and management practices without modification in the selected plots to achieve the best practical results.
Potatoes were sown in furrows and ridges with a row spacing of 70 centimeters and a plant spacing of 60 centimeters, while maize was sown in strips with a row spacing of 60 centimeters and a plant spacing of 15 centimeters. Irrigation was scheduled twice a week, with each session lasting about four hours and applying approximately four liters per meter of drip line at a pressure of about 0.6 bar. The amount of fertilizer required for each plant was determined based on soil tests and was applied in two installments through fertigation: the first installment occurred one hour after irrigation began and lasted for three hours. Soil samples were collected after the first fertigation at intervals of 4, 24, 98, 624, and 1632 hours, with a second round at 4, 24, 98, and 960 hours at horizontal distances of 0, 5, 10, and 15 centimeters, and at depths of 0-5, 5-10, 10-15, 15-20, 25-30, and 30-40 centimeters using the auger method, with two replicates for each sample. Samples were taken from the nearest plant to the sensor, and similar procedures were applied to non-planted control points to minimize spatial variability, assumed to be negligible up to one meter away. The soil samples were immediately transported to the laboratory and stored in a refrigerator for prompt measurement of phosphorus, potassium, nitrate concentrations, and moisture content using standard laboratory methods. Throughout this period, observational data were collected, including soil moisture at depths of 10, 15, 20, 30, 40, and 50 centimeters below the surface using TDR sensors, recorded twice daily. Plant indicators and parameters—such as yield, yield components, root depth, plant height, and leaf area—were measured weekly during the growing season, alongside detailed records of irrigation amounts.
To assess nutrient concentration at planting, nutrient distributions in the soil at a depth of 0-40 centimeters were evaluated by collecting four samples, each 10 centimeters thick, prior to planting. At the end of the growing season and before harvest, a soil profile was excavated for each plant and the control point in areas where TDR sensors were installed. Undisturbed soil samples were collected using metal cylinders at depths of 0-10, 10-20, 20-35, and 40-50 centimeters and sent to the laboratory to determine hydraulic properties, including hydraulic conductivity and moisture retention curves. Additionally, plant samples taken from the same locations as the sensors and fertilizer applications were also analyzed in the laboratory.
For the preliminary evaluation of observational data, the information was interpolated and thoroughly examined. The distribution and movement of phosphorus and potassium in the soil under different plant cultivations were found to vary significantly. Moreover, the assessment of water flow and nutrient movement in the soil, along with their uptake by plants, was conducted through a plant-hydrological model. This model utilized soil moisture and observed concentrations, while hydraulic and hydrodynamic parameters were optimized through an inverse solution method.
The results indicated that splitting fertilization increased nutrient availability in the soil compared to simply increasing the quantity of fertilizer. Distribution patterns for phosphorus and potassium were distinctly different, showing a decrease in concentration with increasing depth. Additionally, it was found that salts in a drip irrigation context moved to a maximum depth of 15 centimeters and horizontally up to 35 centimeters, following the wetting front. These investigations underscored that splitting fertilization in crops with shallow roots (0-40 centimeters deep) is more effective than merely increasing concentration in conditions of low splitting.
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