Pools and raised-beds mode of storage and diversion of water improving water and salt movement and increasing cotton yield in Bohai Rim saline-alkali land

The photosynthetic production and yield of crops are seriously affected by the stress of saline-alkali, drought and waterlogging in Bohai Rim land. Traditionally, pools and raised-beds are built to alleviate the adversity stress in this area. However, the pools and raised-beds are separately functional so that the effects are not well. In this study, a “shallow pools and raised-beds” system for storage and diversion of water, an improved system of traditional system, was established in coastal farmland. In this system, water collected in pools could be used for irrigating crops on the raised-beds. The purpose of this study was to investigate the effects of the system on water-salt movement of saline-alkali fields and cotton production. The system was constructed in 2014 at the state-owned Haixing Farm, Cangzhou City, Hebei Province, China, which was located in 38°21′N and 117°31′E. The experiment was carried out in 2017 and 2018. This system was constituted of three types of fields: raised-bed field (A), shallow groundwater extracted field (B) and salt-restriction and water drained field (C). The field without using this system was considered as control (CK) to clarifying the mechanisms of water-salt movement in fields in this system. Cotton was planted in same pattern in these four types of fields. Soil samples at 0-200 cm depth of four types of cotton fields were collected during the period from April to October of 2017 and 2018 for determination of soil moisture, salt content and pH values. The photosynthesis index (leaf area, SPAD value, net apparent photosynthesis rate, canopy apparent photosynthesis rate and photosynthetic accumulation characteristics) and yield (including its components) of cotton were measured or calculated during the whole growth period of cotton in 2017 and 2018. The effects of their spatial distribution characteristics on the photosynthesis and yield of cotton were also analyzed. Results showed that the soil moisture in the four types of fields was the highest in July and August and the lowest from April to June. Among the four types of fields, the soil moisture was the highest in the CK and the lowest in the field A. In the soil layers of 0-40 cm, the soil moistures of fields A and C were both lower than 20%. Compared to CK, the soil moisture was decreased by 13.0%-46.6% in the field A, 1.9%-23.0% in the field B, and 0.3%-44.0% in the field C, respectively. Similarly, the salt content of field A, B and C was also decreased by 21.1%-77.6% compared to CK. Compared to CK, the pH values of field A and B were both decreased in June and August. Soil salt in cotton field of A and B decreased to about 3.0 g/kg. Soil salt content in cotton field C was below 5.0 g/kg, and soil pH values in July and August were below 8.0. Cotton field A showed the lowest soil moisture, soil salt content and pH value. The seed cotton yield of field A, B and C was 3 500, 3 000 and 2 500 kg/hm2, respectively. The “shallow pools and raised-beds” model of storage and diversion of water greatly changed water-salt movement in cotton field, which was beneficial to cotton production and thus increased the cotton yield in Bohai Rim saline-alkali land. This research provided a scientific model for the efficient exploitation and utilization of coastal saline-alkali land.