Long-term effects of lowland sawah system on soil physicochemical properties and rice yield in Ashanti Region of Ghana

Abstract

Lowland sawah is viewed as a sustainable alternative to traditional rice culture in West Africa. Sawah (a bund-demarcated, puddled, leveled, and water-regulated rice field) has received growing research attention lately, but no data exist yet on the system's long-term agronomic impact. In a clayey inland-valley soil in southern Ghana, 10-year-old sawah plots (OSP), fresh sawah plots (FSP), and non-sawah plots (NSP) were maintained under both ponded and nonponded conditions in 2007. The OSP enhanced soil status of exchangeable nutrients compared to NSP. There were relative improvements in soil bulk density, total porosity, and field moisture content (OSP ≥ FSP > NSP), with clear benefits of ponding over non-ponding in OSP. The NSP was so unsustainable that it showed less favourable values of these variables than an adjacent fallowed plot. These soil variables deteriorated with time, with significant differences in FSP. Soil moisture retention data for tension range of 0-300 kPa depicted the importance of puddling and ponding. These results highlight the agronomic benefits of continuous sawah-based rice production. Although the positive effects of puddling on the soil hydrophysical properties were largely responsible for the wide margin in yield between sawah and traditional systems, other yield-enhancing factors, particularly bunds for water control, were also lacking in the latter.Additional key words: age of sawah; moisture retention; Oryza sativa; ponded sawah plot; rice grain yield; seasonal puddling; soil bulk density. ResumenEfectos a largo plazo de las tierras bajas del sistema Sawah en la región Ashanti de Ghana sobre las propiedades fisicoquímicas del suelo y el rendimiento del arroz Las tierras bajas del sawah (campos de arroz encharcados y delimitados por lomos de inundación, dotados de una buena nivelación del terreno y regulación del agua) constituyen una alternativa sostenible al sistema tradicional de producción de arroz en África Occidental. El sawah ha despertado una creciente atención, pero aún no existen datos concretos sobre su impacto agronómico a largo plazo. En el año 2007, bajo un suelo arcilloso de valle interior, se llevaron a cabo unos ensayos de cultivo de arroz tanto bajo condiciones de inundación permanente como temporal, para comparar parcelas de sawah de 10 años de antigüedad (OSP) con otras de nueva implantación de sawah (FSP) y con parcelas no sometidas al sawah (NSP). Se observó un incremento de la fertilidad del suelo bajo OSP en comparación con NSP. Otras propiedades del suelo, como densidad aparente, porosidad total y contenido de agua a capacidad de campo mostraron únicamente mejoras relativas (OSP ≥ FSP> NSP), indicando los beneficios derivados del encharcamiento sólo en OSP. En NSP se obtuvieron peores resultados que en el caso de los barbechos adyacentes. En FSP,

Comparative assessment of temporal changes in soil degradation under four contrasting land‐use options along a tropical toposequence

“…Notably, there was no significant decline in total C and N under Sawah . In this study area, Obalum et al (Obalum, Oppong, et al, ) reported similar results in Sawah plots over a similar period of about a decade. These results together highlight the potential of lowland Sawah systems of West Africa to enhance water retention and hence soil cooling, a phenomenon that controls excessive decomposition of organic matter in tropical soils (Kyuma, ).…”

“…Addition of nitrogenous fertilizer such as urea and ammonium sulphate without liming commonly practiced in the study area has been reported to decrease the pH of some soils of West Africa (Pierre, Meisinger, & Birchett, ). In the present location, Obalum et al (Obalum, Oppong, et al, ) reported decreases in soil pH of Sawah plots over a similar period of about a decade. They attributed the results to severe weathering and leaching associated with high rainfall in the area, citing Issaka et al ().…”

“…Because total C and N overall tended to decrease, the decline in exchangeable bases could be due to depletion of organic matter (Ali et al, ). The decreases in the topsoil were not evident under Sawah because seasonal puddling increases topsoil clay content and reduces conductivity, thereby reducing the said high mobility of K + and its leaching out of the soil (Obalum, Oppong, et al, ).…”

“…Wakatsuki et al () estimated the potential Sawah ‐rice area in IVs in Ghana and entire West Africa at 0.70 and 9.00 million ha, respectively. This exotic ecotechnology for lowland rice in West Africa is superior to traditional systems in terms of soil quality and rice yields and is viewed as driver of the much‐awaited rice green revolution in the region (Issaka, Buri, & Wakatsuki, ; Buri, Issaka, Senayah, Fujii, & Wakatsuki, ; Nwite et al, ; Obalum, Buri, et al, ; Obalum et al, ). For further reading on the numerous agronomic and ecological benefits of Sawah systems in West Africa, see Wakatsuki and Masunaga (), Buri et al (), Abe and Wakatsuki (), Igwe, Obalum, and Wakatsuki (), and Wakatsuki et al ().…”

Puddling Intensity for Late-season Sawah Systems Based on Soil Hydrophysical Conditions and Rice Performance

“…The superiority of sawah systems over traditional rice (Oryza sativa L.) culture in West Africa is no longer debatable (Nwite et al, 2008;Obalum et al, 2012;Ofori et al, 2005). Sawah is a term adopted from Indonesia referring to an ecologically engineered lowland rice field, one that is properly demarcated using bunds, puddled, leveled and rowtransplanted to a high-yielding variety and, thereafter, kept under regulated flooding and routine fertilization.…”