Abstract
Overcoming constraints that poorly structured lowland rice-growing soils of the Lower Mekong River Basin present for growing non-rice crops during the dry season would have a significant positive impact on the livelihood of smallholder farmers. This study investigated whether the use of soil organic amendments, bed architecture (conventional, flat and narrow) and water application methods (sprinkler, furrow and over-bed irrigation) could improve plant water availability in typical rice-growing soils of Cambodia and Laos by either improving the movement of water into beds or the growth of the root system. Five experiments were conducted over two dry seasons on peanut and maize grown in a bed/furrow system. Organic amendments assessed were rice straw, cow/goat manure, biochar, manure plus rice straw and biochar plus manure. Results showed that compared with conventional bed/furrow design, narrowing beds increased soil moisture availability for peanut, whilst higher grain yield and water productivity were achieved with sprinkler irrigation than furrow irrigation. Placing a layer of sub-surface straw within beds did not consistently enhance soil moisture or improve root development. The study showed that maize grown on soil amended with biochar plus cow manure under a furrow irrigation system and on rice straw under sprinkler irrigation produced yields above the average yield that models have simulated for maize grown on these soils. These findings present opportunities to enhance maize production on lowland soils across Cambodia and Laos. The contrary was observed for peanut production, which indicates that factors other than water might be detrimentally affecting crop yields.
Highlights
It is estimated that agriculture provides livelihoods for approximately 60% of the population in the Lower Mekong River Basin (LMB) [1]
Since ~25% more water was applied in the furrow-irrigated treatments with no effect on yield, the higher apparent water productivity of the FB-Sprinkler irrigation (SI) and CB-SI treatments was most likely due to improved efficiencies as a product of less water losses associated with sprinkler irrigation
In a conventional bed and furrow irrigation system, it was hypothesized that the inclusion of a layer of straw buried below the topsoil would enhance the lateral movement of water into beds and increase soil moisture retention
Summary
It is estimated that agriculture provides livelihoods for approximately 60% of the population in the Lower Mekong River Basin (LMB) [1]. The LMB covers land of four south east Asian nations, Thailand, Laos, Cambodia and Vietnam, and is currently home to approximately 60 million people. Among the countries through which the Mekong River passes, Cambodia and Laos have been identified by the United Nations World Food Programme as two of the most impoverished nations in southeast Asia, with high rates of poverty, food insecurity and poor nutrition, amongst small landholders. Due to the tropical climate that characterizes the LMB with annual wet (>2000 mm) and dry cycles, smallholder production of rain-fed rice is the main agricultural activity in this region. Most of the rice production area (80%) is concentrated in the lowlands of the LMB where there are limited opportunities for growing alternative crops to rice, during the wet season
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