Can Drainage, Dolomite, and natural phosphate application control iron and sulfide content in iron-toxic irrigated rice fields?

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Résumé

Soil iron (Fe II) and sulfide toxicities are major constraints to irrigated rice productivity in Burkina Faso, West Africa. This study aimed to mitigate these challenges by trialing drainage, fertilization, and iron-tolerant rice varieties, considering seasonal variations. Field experiments were conducted in the dry and rainy seasons using two rice varieties: FKR76 (iron-sensitive) and FKR62N (iron-tolerant). Two drainage modes (D0: no drainage, D2: drainage every 14 days) and eight fertilization treatments were tested: unfertilized (F1), NPK + urea (F2), NPK + Urea + Dolomite + Zn (F3), and NPK + Urea + Natural Phosphate (F4), and each fertilization regime combined with organic manure (FO) and without organic manure (SFO). Soil samples were collected before rice plant transplanting to evaluate the number and activities of Iron-Reducing Bacteria (IRB) and Sulfate-Reducing Bacteria (SRB). At 60 days after transplanting (DAT), the soil Fe II and sulfide concentrations were measured. The results showed that both IRB and SRB activities were higher during the rainy season (p < 0.001) than during the dry season. The FKR76 plots showed higher Fe II concentrations than the FKR62N plots. Organic manure increased sulfide content (p = 0.048), and NPK + urea raised Fe II concentration in the soil (p = 0.045). However, amendments with dolomite and natural phosphate significantly decreased the soil Fe II (p = 0.005) and sulfide (p < 0.001) contents. The treatments applied had no significant effect on the productivity of the FKR62N rice variety. However, the D2FOF2, D2FOF3, D2FOF4, and D0FOF3 treatments significantly improved the tillering (p = 0.000), panicle development (p = 0.000), and grain yield (p = 0.0001) of the iron-sensitive rice variety (FRK76). These results indicate that dolomite and natural phosphate can effectively reduce iron and sulfide toxicity in rice fields across seasons, offering a promising strategy for sustainable rice production under challenging soil conditions.

Mots-clés

Toxicity, Season, Fertilization, Drainage, Rice Variety