Effect of puddling on soil desalinization and rice seedling survival in the Senegal River Delta

Soils in the Senegal River Delta are naturally sodic and saline due to the presence of fossil salt deposits in the subsoil. Such soils are being used for rice (Oryza sativa L.), using pump irrigation. Before the onset of the growing season, farmers dry till and flush their rice field with fresh irri gation water to wash out salts from the root zone. We tested the potential of plowing under water-saturated conditions (puddling) to increase the amou nt of salt washed out from the topsoil with surface drainage. In a 1995 fie ld experiment, salt removal using conventional dry soil-tillage and five ir rigation-drainage cycles was compared with wet tillage (1, 2 or 3 times pud dling) using a hydro-tiller and five irrigation-drainage cycles. Repetitive puddling and surface water drainage was very effective in removing salt fr om the soil profile. Each puddling, followed by surface drainage removed ca . 4.3 t salt ha(-1), as opposed to approximate to 1 t salt ha(-1) per flush ing in the dry tilled plots. However, depth of the puddled layer increased after each puddling, and new salt from the subsoil was, therefore, brought in solution. Puddling had a negative effect on rice seedling establishment, presumably because it induced a lower but homogeneous salt distribution in the puddled layer. We concluded that introduction of the hydro-tiller in t he Senegal River Delta as a replacement for conventional dry tillage cannot be recommended. The hydro-tiller may be used to accelerate reclamation of highly saline areas for rice cropping if a constant tillage depth can be ma intained, and if the soil is allowed to regain structure after puddling. Be fore a reclaimed field is direct-seeded, test sowing and monitoring of surv ival rate for at least a week is recommended. (C) 1999 Elsevier Science B.V . All rights reserved.