Straw retention coupled with mineral phosphorus fertilizer for reducing phosphorus fertilizer input and improving cotton yield in coastal saline soils

• Straw retention combined with fertilizer P application improved soil nutrient status and reduced the adsorption of soil P. • Straw retention enhanced cotton phosphorus uptake, soil P activation coefficient and phosphorus use efficiency of cotton, leading to increased yield. • Mineral P fertilizer can be reduced approx. 27–38 % with crop straw addition. Straw return can improve soil nutrient availability, but its interaction with phosphorus (P) fertilizer on cotton ( Gossypium hirsutum L.) production and soil P availability has rarely been studied. Therefore, we carried out a four-year field trial to evaluate the effects of straw management (retention or removal) with P fertilizer (0, 22, 44, 66, 88 kg P ha –1 ) additions on seed cotton yield, cotton P uptake, soil fertility, and P apparent recovery efficiency (PRE) in a continuous barley–cotton rotation system in a coastal saline soil field from 2016-2019. Our results showed that the year and the interaction of P fertilization and straw management had significant effects on seed cotton yield and boll numbers, but there was no significant effects of straw management and the interaction of P fertilization and straw management on seed cotton weight per boll. An increase in P activation coefficient (14-28%) was observed due to the higher soil available P content following straw retention compared to the straw removal. Compared with straw removal, straw retention reduced mineral P fertilization by about 27-38% without affecting seed cotton yield, while increasing PRE by 14‒27% over the four years. In the 0-20 cm soil layer, straw retention reduced the Langmuir P sorption maximum (Q max ) and maximum buffer capacity (BC max ), and also increased the degree of P saturation (DPS), but it did no effect on the soil adsorption equilibrium constant (k). Straw retention significantly decreased the soil Q max compared to straw removal under 0, 22, and 44 kg P ha –1 , while no significant straw effects were found on Q max under 66 and 88 kg P ha –1 . Cotton P uptake and seed cotton yield were negatively correlated with the Q max (P<0.01). Our results suggest that straw return may be a promising management practice to reduce mineral P fertilization without significant loss of seed cotton yield on coastal saline lands.