Effect of variable and fixed alternate furrow irrigation on salinity, phosphorous and potassium concentration in soil of sugarcane field

Introduction:

 The highest amount of water consumption is allocated to the agricultural sector, which has led to a water crisis due to increasing demand for food production and non-conservative agriculture and climate change in some countries. Sugarcane needs a lot of water during the growing season and is sensitive to drought. In drought conditions and water stress, the intensity of reverse flow of water to the soil surface increases and can cause salinization of the soil around the roots of sugarcane, which is a relatively sensitive plant related to salinity. Due to the high-water consumption in sugarcane fields and also the shortage and decline of water quality in dry years, this study aimed to investigate the effect of conventional and deficit irrigation by variable and fixed alternate furrow irrigation on soil salinity and some nutrient concentration consist of phosphorous and potassium in sugarcane field.

Materials and Methods:

 To investigate the effect of irrigation methods on salinity distribution and concentration of phosphorous and potassium in soil, this experiment was conducted with independent variables of irrigation method treatment including conventional (complete) irrigation, variable alternate furrow irrigation and fixed alternate furrow irrigation, irrigation round treatment including before irrigation, after one and two times irrigation, sampling location treatment including bottom, middle and top of raised bed and sampling position treatment consist of start, middle and end of furrow. The experiment was performed factorially in a completely randomized design with three replications in sugarcane fields of MianAb in Susa. Statistical analysis was performed using SPSS software and mean comparisons were performed by Duncan's multiple range test. Charts were drawn using Excel software.

Results and Discussion:

 The results showed that irrigation method is mainly affects salinity distribution and concentration of phosphorus in soil. The fixed alternate furrow irrigation method had the greatest effect on soil salinity changes and reduced the salinity as compared to the conventional method and the variable alternate furrow irrigation. In general, in the conventional irrigation method (complete irrigation of all furrows) and variable alternate furrow irrigation, there is no constantly dry furrow as compared to the fixed alternate furrow irrigation method, and this intensifies the accumulation of salts on the sides and the top of raise beds. Increasing the frequency of irrigation (irrigation round) reduces the soil salinity so that in soil samples before irrigation, soil salinity was 2.30 dS/m and with one round irrigation, this amount decreased by 7.8% to 2.12 dS/m and with two rounds of irrigation reached to 2.09 dS/m. In terms of locative variation of salinity related to the fixed alternate furrow irrigation method, the lowest amount of salinity was observed in the bottom of the raised bed. With increasing distance from the beginning of furrow, an upward trend in soil salinity was reported. Regarding the change in the amount of available phosphorus in the soil under the influence of irrigation method, any of the deficit irrigation methods can be used as an alternative to conventional irrigation. The highest amount of soil phosphorus was reported in the middle of the raise bed. Soil potassium changes were not directly affected by irrigation method and the highest amount was assessed in the bottom of the raise bed. In terms of salinity, the lowest value was at the bottom of the furrows and the highest value was at the top of the raise bed. Unlike salinity changes, soil phosphorus had the highest accumulation in the middle of the raise bed and reached a minimum at the top of the raise bed. A relatively uniform trend was observed in changes in soil phosphorus from the beginning to the end of the furrow. Contrary to salinity changes, the highest amount of available potassium in soil was observed in the bottom of raise bed and a decreasing trend in soil potassium was reported from the beginning to the end of furrow. In general, based on the results, the average level of soil salinity and potassium and the highest amount of phosphorus were reported in the middle of the raise bed.

For optimal water use and soil salinity management, application of deficit irrigation methods especially fixed alternate furrow irrigation instead of conventional irrigation method, is recommended. In case of salinity and concentration of mentioned nutrients, the top of the raise bed in all three irrigation methods, would not be a suitable place for plant cultivation.