Influence of Rice Straw Mulching on Soil Available Silicate and Maize Growth in Paddy Fields Affected by Saline Intrusion in the Mekong River Delta, Vietnam

In Vietnam, Si accumulator crops like rice and maize crops are commonly rotated, but rice straw is often removed for animal feed. This study assessed whether rice straw mulch could improve soil available Si and maize growth. A field experiment was conducted over three years in two fields with different soil Si levels. Four rice straw mulch levels (0, 3.5, 7, and 10.5 t ha⁻1) were applied during the maize growing season (Feb–Apr), and repeated for three years. In the 3rd year, soil samples were analyzed for available Si (phosphate buffer extraction) and Si fractions (CaCl2-Si, acetic acid-Si, H2O2-Si, oxalate-Si, and NaOH-Si). Maize yield and Si, N, P, K, and Na uptake were also evaluated. At the lower available Si field, rice straw mulch significantly increased the phosphate buffer-Si, CaCl2-Si and H2O2-Si in soil two weeks after sowing whereas the higher available Si field showed no differences among treatments. In contrast, the Si concentration in maize stems and leaves increased notably in the higher rice straw treatments at both sites. Furthermore, a negative correlation was found between Si and Na concentrations in the maize stems and leaves, suggesting that Si may play a role in mitigating Na uptake and reducing Na toxicity. This study demonstrated that the application of 7 and 10.5 t ha⁻1crop⁻1 of rice straw to fields with low available Si may enhance the soil Si availability, and improve Si, N, P, K uptake and tolerance to salt stress.