Investigating the accumulation of salts in the soil under sugarcane cultivation in subsurface drip irrigation

Abstract

Introduction

Soil salinity can cause the destruction of arable land and sustainable production. Increasing the concentration of salts beyond the tolerance threshold causes irreversible physiological damage to the plant. The essence of soil salinity control measures is to regulate the movement of water and the transport of salts downward and out of the area of root development and to prevent their accumulation and transport to the soil surface due to evaporation and transpiration. Subsurface drip irrigation helps improve irrigation efficiency and reduce salinity. But careful design and management are essential to control water salinity. Considering the necessity of optimal irrigation water consumption and the development of subsurface drip irrigation in sugarcane fields in Khuzestan and the important role of soil salinity, studying changes in soil salts and their distribution in different irrigation methods and irrigation management in arid and semi-arid conditions is of great importance.Therefore, this study was conducted to investigate the effect of fertilization stages in subsurface irrigation on salt accumulation, sodium absorption ratio, ammonium and nitrate levels at different soil depths in the root development zone of sugarcane under a subsurface drip irrigation system.

Materials and Methods

The study was conducted in the Farabi Sugarcane Agro-Industry in during the agricultural year 2021-2022, in 35 km from the Ahvaz-Abadan road, east of the Karun River. Before cultivation, the physical and chemical properties of the soil were determined. After preparing and creating the furrow and ridge, sugarcane cuttings of the CP69-1062 variety were planted in two rows with a distance of 40 cm from each other. The Water tube was placed in the middle of two rows of cuttings. In-line dripper pipes with a diameter of 20 mm, dripper spacing of 50 cm, and dripper flow rate of 2.4 L/ha were installed at a depth of 20 cm below the soil surface. The average EC of irrigation water during the research period was 3.18 dS/m. Irrigation planning and water requirements for sugarcane plant were based on the five-year average of evapotranspiration, plant coefficients, and evaporation pan coefficient, taking into account the appropriate irrigation interval. Nitrat fertilization was done at a rate of 300 kg/ha, 25 kg/ha per time. Sampling to evaluate soil salt accumulation was carried out in six stages, a one week after fertilization. EC, pH, concentrations of calcium, sodium and magnesium, ammonium and nitrate dissolved in the saturated extract were measured. In order to investigate the effect of fertilization, a factorial split-plot experimental design with three replications was used. The fertilization stages treatment consisted of six stages (T1, T2, T3, T4, T5, and T6), while the soil depth treatment included five depths (0-20, 20-40, 40-60, 60-80 and 80-100). For analyze the results was used SAS ver 9.4 software, also using the LSD test method, the means of main effects and interaction effects were compared.

Results and Discussion

The results showed that the highest and lowest pH measured occurred in T3 and T4 respectively.The highest electrical conductivity of 4.55 dS/m in stage T4 and the lowest electrical conductivity of 3.01 dS/m was observed in stage T1.Also, the highest EC at a depth of 20 cm is equal to 5.34 dS/m.NH4+ was highest in T1 stage at all depths compared to other fertilization stages.The highest and lowest NO3- were measured in T5 and T2equal to 30.47mg/kg and 20.11mg/kg, respectively. The upward trend in nitrate in each stage compared to previous stages is likely due to increased nitrification that occurred from the application of each fertilizer stage. In depth of 20 cm, the concentration of NO3-soil, equal to 33.54 mg/kg, is higher than at other sampled depths. This trend could be due to the subsurface drip irrigation system, where the depth of penetration of the moisture bulb is less than this range. The interaction between fertilization stages and sampling depth showed that the highest SAR was at the time of fertilization stage T4 and a depth of 20 cm from the soil surface (11.31) and the lowest SAR was at the time of fertilization stages T1 and T6 and a depth of 80 cm (4.66 and 4.57, respectively). In this study, the increase in sodium absorption ratio (SAR) was not affected by the quality of irrigation water, but rather by the type of irrigation method (subsurface drip) and the depth of drip installation.

Conclusion

The results of this study showed that nitrogen fertilizer application had a variable effect on soil pH during the period. This process could be due to microbial activity, mineralization, and nitrification processes. The highest pH measured was in the third stage and the lowest in the fourth stage of fertilization. The highest soil salinity is due to the interaction between fertilization stages and soil depth at the fourth fertilization stage and a depth of 20 cm, which has increased by 54.7 percent compared to the same depth in the first stage. The highest ammonium concentration was in the first stage, which was 28.3 percent higher than the lowest concentration measured in the second stage. Also soil nitrate concentration showed that the highest and lowest concentrations were in the fifth and second stages, respectively, with a difference of 67.15 percent between them. Totally, the concentration of ammonium and nitrate in the soil depth has been decreasing. The behavior of the exchange sodium adsorption ratio is similar to electrical conductivity and increased during the study, which was intensified at the soil surface due to the depth of soil moisture penetration and irrigation method. Therefore, the results of this study indicate that in order to manage salts and prevent their accumulation at the soil surface in sugarcane cultivation areas in Khuzestan using subsurface drip irrigation, it is recommended to consider flow rate and installation depth of the drippers should be considered further.