Effect of humate and controlled released NPK fertilizers (NPK-CRF) on rice yield and soil fertility of intensive alluvial soils

The study aims to assess the effect of mixed fertilizers, including controlled slow-release NPK (NPK-CRF) and urea, potassium humate fertilizers, on soil fertility and rice yield. The on-Farm Trials experiment was carried out on alluvial soil, with two models corresponding to two farming techniques: (i) Traditional fertilization, applying conventional fertilizers with the formula 92.2 N–82.8 P2O5–22.8 K2O kg/ha; (ii) New generation fertilizers (NPK-CRF, urea humate, and potassium humate) with the formula 50.1 N–39.9 P2O5–30.0 K2O. Each pattern was repeated three times, corresponding to 3 farmers. Each household's area is 1,000m2, cultivating continuously through three seasons of Winter-Spring (WS), Summer-Autumn (SA), and Autumn-Winter (AW) in Chau Thanh A district, Hau Giang province. The results showed that the new generation fertilizer application significantly improved rice yield and yield composition of the Winter-Spring cropping season (6.92 tons/ha), Summer-Autumn (5.94 tons/ha), and Autumn-Winter (6.15 tons/ha), which are different from farmers' fields. Furthermore, the combined application of NPK-CRF, urea-humate, and K-humate fertilizers for rice in SA and AW crops significantly reduced the total acid content, Al3+ exchange in the soil, and improved soil fertility of pH, N, and available P, organic matter (%C). However, there was no difference in soil's physical properties over the three farming seasons. Finally, adding humic acid to controlled-release fertilizer can improve soil fertility, and increase yield and yield components, nitrogen uptake, enhance nitrogen usage efficiency, all of which have positive yield and soil consequences.