No-till with straw return retains soil total P while reducing loss potential of soil colloidal P in rice-fallow systems

Colloidal phosphorus (P) migration has been confirmed to be an important pathway for P loss in farmland. A field experiment was conducted with four treatments and three replications: conventional tillage/straw harvest (CH), conventional tillage/straw return (CR), no-till/straw harvest (NH), and no-till/straw return (NR) to clarify the effect of conservation agricultural practices on concentration of soil total P, available P, P stocks, and colloidal P during a 2-year rice-growing season in Zhejiang Province in China. The results showed that the soil total P and available P content increased significantly at the end of the two years compared with that before the experiment (P < 0.05), by 18.80–38.90 mg kg–1 and 1.12–1.55 mg kg–1 in clay soil, and by 20.70–35.70 mg kg–1 and 1.81–2.17 mg kg–1 in loam soil. While the total P accumulation in both soil types mainly occurred during the rice-growing season. The highest P stocks (293.90 and 136.80 g m−2) in the two soils were found in the NR treatment. In contrast, soil colloidal P significantly declined during the two-year rice-fallow period. The CR and NR treatments resulted in the lowest colloidal P contents (6.1 mg kg–1 and 3.6 mg kg–1) and accounted for the lowest percentage of total P (0.6% and 0.8%) in clay loam and loam soils, respectively. Straw return/harvest and no-till/till had an interactive effect on the soil colloidal P content. The combination of no-till and straw return is an effective way to reduce loss potential of soil colloidal P in a rice-fallow system but varies by soil texture.