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In the soil column experiments, the irrigation amount varied from 4.8 to 12 L, and the nitrogen application rate was from 80 to 360 kg ha−1. Three fertigation strategies were tested. The results indicated that an increase in water input led to an increase in the area of pH decrease in the soil at 10 days after the irrigation ended for a given lateral depth of 10 cm. The measurement of nitrogen distribution showed that the nitrogen content in the soil was significantly increased with the nitrogen application rate. Fertigation strategies substantially affect the pH and nitrogen distributions in soil. The strategy of applying water at first for one-fourth of the total irrigation time (1/4W), then applying fertilizer solution for one-half of the total irrigation time (1/2N), followed by applying water for the remaining one-fourth of the total irrigation time (1/4W) made a minimal soil pH decreasing area and a homogeneous nitrate distribution at 0–20 cm depth. Therefore, to reduce NO3-N leaching and avoid deep soil acidification, a dripline depth of 10 cm with an irrigation amount of 4.8 L and a nitrogen application rate of 80 kg ha−1 through the 1/4W–1/2N–1/4W fertigation may be suggested. HIGHLIGHTS Minor water and nitrogen input with shallow lateral depth can be conducive to reduce nitrate leaching.; The NO3-N accumulation and pH decrease mainly appeared in surface soil through 1/4W–1/2N–1/4W fertigation.; Drip irrigation is feasible to mitigate soil acidification.; An ongoing field experiment confirms and improves the results of laboratory experiments without crops.;

The understanding of soil and nutrient dynamics under drip fertigation is relevant for crop production as well as water and nutrient management. The aim of this study was to generate information about the distribution of phosphorus (P) under different fertigation strategies for onion production on sandy clay loam soil during 2007-2008 to 2008-2009. The study involved field experiment, laboratory analysis and modeling of P distribution. The phosphorus distribution data in the field were collected, analyzed and used to calibrate and validate the solute transport model HYDRUS-2D for sandy clay loam soil. The performance of HYDRUS-2D was evaluated by comparing its simulated values with the observed values of soil moisture and nutrient concentration. The coefficient of determination (R 2), root mean square error (RMSE) and mean absolute error (MAE) were used as model performance indicators. The range of R2 between 0.72-0.99 for water as well as nutrient distribution indicates good correlation between the observed and simulated values. The MAE and RMSE values for water and nutrient distribution were in between 0.0009 to 0.0039 which indicated the accuracy of the model. From these results, it can be concluded that the model is performing well for predicting the P concentration in the soil as well as the soil moisture distribution for onion crop grown under sandy clay loam. The model was also validated for water and phosphorus distribution with the observed values at the end of the crop season and found to be performing well. The HYDRUS-2D model may be used to carry out simulations for different soil types and with different fertigation and irrigation strategies for developing guidelines. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of optimal water and nutrient management is to maximize water and fertilizer use efficiency and crop production, and to minimize groundwater pollution. In this study, field experiments were conducted to investigate the effect of soil salinity and N fertigation strategy on plant growth, N uptake, as well as plant and soil 15N recovery. The experimental design was a 3×3 factorial with three soil salinity levels (2.5, 6.3, and 10.8dSm−1) and three N fertigation strategies (N applied at the beginning, end, and in the middle of an irrigation cycle). Seed cotton yield, dry matter, N uptake, and plant 15N recovery significantly increased as soil salinity level increased from 2.5 to 6.3dSm−1, but they decreased markedly at higher soil salinity of 10.8dSm−1. Soil 15N recovery was higher under soil salinity of 10.8dSm−1 than those under soil salinity of 6.3dSm−1, but was not significantly different from that under soil salinity of 2.5dSm−1. The fertigation strategy that nitrogen applied at the beginning of an irrigation cycle had the highest seed cotton yield and plant 15N recovery, but showed higher potential loss of fertilizer N from the root zone. While the fertigation strategy of applying N at the end of an irrigation cycle tended to avoid potential N loss from the root zone, it had the lowest cotton yield and nitrogen use efficiency. Total 15N recovery was not significantly affected by soil salinity, fertigation strategy, and their interaction. These results suggest that applying nitrogen at the beginning of an irrigation cycle has an advantage on promoting yield and fertilizer use efficiency, therefore, is an agronomically efficient way to provide cotton with fertilizer N under the given production conditions. [Copyright &y& Elsevier]

Frequent application of nitrogen fertilizers through irrigation is likely to increase the concentration of nitrate in groundwater. In this study, the HYDRUS-2D/3D model was used to simulate fertilizer movement through the soil under surface (DI) and subsurface drip irrigation (SDI) with 10 and 20 cm emitter depths for tomato growing in three different typical and representative Egyptian soil types, namely sand, loamy sand, and sandy loam. Ammonium, nitrate, phosphorus, and potassium fertilizers were considered during simulation. Laboratory experiments were conducted to estimate the soils' adsorption behavior. The impact of soil hydraulic properties and fertigation strategies on fertilizer distribution and use efficiency were investigated. Results showed that for DI, the percentage of nitrogen accumulated below the zone of maximum root density was 33%, 28%, and 24% for sand, loamy sand, and sandy loam soil, respectively. For SDI with 10 and 20 cm emitter depths, it was 34%, 29%, and 26%, and 44%, 37%, and 35%, respectively. Results showed that shallow emitter depth produced maximum nitrogen use efficiency varying from 27 to 37%, regardless of fertigation strategy. Therefore, subsurface drip irrigation with a shallow emitter depth is recommended for medium-textured soils. Moreover, the study showed that to reduce potential fertilizer leaching, fertilizers should be added at the beginning of irrigation events for SDI and at the end of irrigation events for DI. As nitrate uptake rate and leaching are affected by soil's adsorption, it is important to determine the adsorption coefficient for nitrate before planting, as it will help to precisely assign application rates. This will lead to improve nutrient uptake and minimize potential leaching. [ABSTRACT FROM AUTHOR]