Cambodians love their food and love eating it with company. No one should eat alone, they say. It’s not surprising they appreciate sitting down with friends, family, and workmates to multiple plates piled with steaming greens, succulent meats, and a hefty serving of rice, as the horrific past of hunger, community dislocation, and nationwide devastation lingers in the not-too-distant past (see Revisiting the “Killing Fields”).
Rice culture and cultivation
The staple food of Cambodians is rice. Only a few kilometers out from the capital city of Phnom Penh are verdant rice paddies offering a tranquil reprieve from the city’s hustle and bustle.
Rice-based farming systems have been the mainstay of rural livelihoods in Southeast Asia for centuries. However, trends suggest an increasing diversification and intensification1 within these systems, which are opening up new opportunities for farmers as well as highlighting existing production constraints.
Puddling or wet cultivation is the traditional method of land preparation for establishing rice─a practice that destroys soil aggregates, breaks the capillary pores through which water enters, disperses clay particles, and lowers soil strength in the puddled layer.2–4 Repeated puddling leads to the formation of a dense layer of soil or hardpan below the topsoil layer that helps retain water in flooded rice fields. The hardpan has high bulk density, which reduces water loss through drainage and allows the field to maintain standing water required in growing the rice crop.
Going beyond rice
In continuous rice culture, the formation and maintenance of the compacted lower soil layer that reduces water infiltration can be considered an investment in infrastructure. In the rice–nonrice system, however, the destruction of surface soil structure and the development of the hardpan can impose serious liabilities on the establishment and performance of crops grown after rice.
In Cambodia, hard-setting soils are widespread and strongly influence crop production during the dry season as these tend to limit the retention, movement, and plant use of water and nutrients.6 This is due to two contrasting unfavorable physical conditions at different water contents, namely, the complete breakdown of large, air-dry soil aggregates into microaggregates with sudden immersion in water (slaking)7,8 and an extremely hard structureless mass formed during drying9, with a positive correlation between hard-setting and bulk density.10
Irrigation or rainfall after sowing can cause the soil surface to collapse while the subsequent drying may harden the surface, preventing the seedlings from emerging11 or impeding the root growth of established plants.9
Growing dry-season crops after rice on hard-setting soils can pose serious challenges for farmers in Cambodia. Further understanding how land formation techniques (leveling, grading, and raised-bed construction) for improved water and nutrient management and efficiencies affect soil structure and the behavior of nutrient and water dynamics is required to develop refined and integrated management practices and realize the potential of high-value non-rice crops.