Combined organic amendments and mineral fertilizer application increase rice yield by improving soil structure, P availability and root growth in saline-alkaline soil

In saline-alkaline soil, soil structural stability and phosphorus (P) availability are the limiting factors for crop yield. Organic amendments are proved to play a key role in soil quality, P availability and plant growth. A field experiment was carried out with different organic amendments level in the Yellow River Delta, five treatments were designed: (i) Control (no fertilization), (ii) NK (255 kg N ha⁻¹ year⁻¹ and 229 kg K ha⁻¹ year⁻¹), (iii) NPK (128 kg P₂O₅ ha⁻¹ year⁻¹ plus NK), (iv) NPKC1 (450 kg C ha⁻¹ year⁻¹ plus NPK) and (v) NPKC2 (900 kg C ha⁻¹ year⁻¹ plus NPK). The main results showed that: compared with NPK treatment, the mean weight diameter (MWD) of soil aggregates was increased by 33.8 % and 47.1 % in NPKC1 and NPKC2 treatments, respectively. And the percentage of water-stable aggregate (WSA) was also improved by 30.5 % and 40.16 % in NPKC1 and NPKC2 treatments, respectively. This was due to the increase of soil exchangeable Ca, soil organic carbon (SOC) and particulate organic carbon (POC) content, and the decrease in soil bulk density and exchangeable Na content, as well. Meanwhile, soil available P (AP), total P (TP), dicalcium P (Ca₂-P) and octacalcium P (Ca₈-P) contents were significantly increased with organic amendments addition. Based on the increase of soil structural stability and P availability, especially the accumulation of inorganic P (Pᵢ) in soil macro-aggregates, root surface area and plant P use efficiency (PUE) were improved, which resulted in the grain yield increased by 12.2 % and 16.6 % in NPKC1 and NPKC2 treatments, respectively. Consequently, combined organic amendments and mineral fertilizer application were better in improving the soil structural stability, P availability and plant growth in saline-alkaline area.