Effects of irrigation frequency on transportation and accumulation regularity of greenhouse soil salt during different growth stages of pepper

Abstract

Mismanagement of irrigation and fertilization has led to soil salinization in the greenhouse. This study was to evaluate the impact of irrigation frequency on greenhouse soil salt content and salt ions' distribution, and find a proper irrigation frequency for each growth stage of pepper cultivated in greenhouse. Simulated laboratory experiments were carried out using the soil box. This study contained three different types of irrigation frequencies: 5 d, 10 d and 15 d, and the times of irrigation were 13, 7 and 5, respectively. In the first water circle of the seedling, squaring and mature stage of pepper, soil samples were collected from the soil box on the days before and after irrigation. Soil salt content and soil salt ion contents were determined. The ratio of desalinization increased with the decrease of irrigation frequency. The main salt ions in the soil were Ca2+, SO42− and NO3−, and the percentages of Ca2+, SO42− and NO3− were 25.08%–43.94%, 14.80%–49.81% and 8.60%–46.47% in the whole stages of pepper. The results showed that there was a different phenomenon between SO42– and Ca2+ when they aggregated at the plough profile. SO42– easily aggregated at the plough profile under 5 d and 15 d treatments, in contrast to that Ca2+ dramatically aggregated at the surface profile under 15 d treatment. Irrigation frequency of 10 d with intermediately single irrigation amounts was more reasonable before the mature stage, and irrigation frequency of 5 d with small single irrigation amounts was the best during the mature stage of pepper. However, irrigation frequency of 15 d with large single irrigation amounts could easily cause serious salt leaching in soil profiles and even groundwater pollution. The leaching of soil salt ions were affected by irrigation, with decreasing influence on NO3−, Ca2+ and SO42− especially in NO3−, which was harmful for groundwater environment. The transportation of salt in soil was influenced by preferential flow, and the potential influence of preferential flow decreased with the reduction of irrigation frequency. There existed preferential flow at the squaring stage of pepper under 5 d treatment and at the mature stage of pepper under 10 d treatment.