Phosphorus placement and water-saving technologies can improve rice production in phosphorus-deficient lowlands in SSA

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Lowland rice production in sub-Saharan Africa (SSA) is often limited by water supply and low soil phosphorus (P) availability and efforts are needed towards more efficient management of both resources.

Additionally, crop roots are highly important for both water and P acquisition from the soil, and hence root performance plays a critical role determining water and P use efficiency.

Field and pot experiments were set up to evaluate combinations of water saving technologies (such as alternate wetting and drying, and aerobic rice) and P placement methods (i.e. the localized application of a small P fertilizer dose to a sub-surface area, often combined with seeds into the planting hole) with due attention to treatment effects on root architecture.

P applied to soil as fertilizer moves away from the point of application mainly through diffusion, while sorption and precipitation reactions may reduce its mobility and availability to plants. Therefore, P diffusion and sorption outwards contrasting application rates of P placements was modeled under different water regimes to assess the combined effects on P availability to the rice crop.

It was shown that reduced water supply (i.e. at field capacity compared to soil saturation) restricted P diffusion, hence reduced P immobilization, and so increased total P availability from placements. These differences between water treatments were more pronounced at lower than at higher P supply and were confirmed on the field.

This study, which was carried out by scientists from Catholic University of Leuven, International Potato Center (CIP) and Africa Rice Center (AfricaRice), shows that both root responses and P diffusion outwards placed granules explain rice development and yields under P placement and water saving technologies. Obviously, broadcasting a large P rate remains advisable under P deficiency, but resource limitations may hamper such amendments.

“We argue, therefore, that P placements can contribute to intensify lowland rice production while countering soil P declines in P deficient lowlands,” explained Dr Pieterjan De Bauw, Division of Soil and Water Management, Catholic University of Leuven, who led the study.

“Without P application or when applying small P placement rates, interactions with water management should definitely be considered as water saving technologies were observed to enhance P uptake, enhance rice development, and increase yields in such situations,” he added.

The findings of the study were revealed in the article “Combining phosphorus placement and water saving technologies enhances rice production in phosphorus-deficient lowlands” by De Bauw P., Vandamme E., Senthilkumar K., Lupembe A., Smolders E., Merckx R., published in the journal Field Crops Research, 236, 177-189.

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