Journal Article

Phosphorus cycling in rainfed lowland rice ecosystems on sandy soils

Pheav, S, Kirk, G.J.D, White, P.F, Bell, R.W

2005

Overview

Phosphorus cycling in rainfed lowland rice ecosystems is poorly understood. Soil drying and grazing of rice straw during the long dry season, the growth of volunteer pastures during the early wet season, and intermittent loss of soil-water saturation while the rice crop is growing are important distinguishing characteristics of the rainfed lowlands in relation to P cycling. We studied P cycling in an acid sandy rainfed lowland soil that covers about 30% of the rice growing area of Cambodia. Soils with similar properties in comparable rainfed sub- ecosystems occur in Laos and northeast Thailand. We developed a general schema of P pools and fluxes in the crop and soil for rice-based cropping systems in the rainfed lowlands of Cambodia. The schema was derived from a number of field experiments carried out over five consecutive cropping seasons to quantify the residual value of P fertiliser, P mass balances, soil P fractions, the effect on subsequent rice crops of crop residues and volunteer pastures incorporated into the soils, and the dynamics of P turnover in the soil. With a single rice crop yielding 2.5–3 t ha-1, application of 8–10 kg P ha-1 maintained yields and a small positive P balance in the soil. However, the soil P balance was sensitive to the proportion of rice straw returned to the soil. Volunteer pastures growing during the early wet season accumulated significant amounts of P, and increased their P uptake when soils were previously fertilised with P. These pastures recycled 3–10 kg P ha-1 for the succeeding rice crops. While inorganic soil P pools extractable with ion exchange resins and 0.1 M NaOH appeared to be the main source of P absorbed by rice, microbial and organically-bound P pools responded dynamically to variation in soil water regimes of the main wet, dry and early wet seasons. The schema needs to be developed further to incorporate site-specific conditions and management factors that directly or indirectly affect P cycling, especially loss of soil-water saturation during the rice cropping cycle. The paper discusses the application of results for acid sandy soils to other significant rice soils in the rainfed lowlands of southeast Asia.

• Publisher: Springer,Springer Nature B.V
• Subject: 2nd International Symposium on Phosphorus Dynamics in the Soil-Plant Continuum / Acid soils / agricultural soils / Agrology / Agronomy. Soil science and plant productions / Biological and medical sciences / Cambodia / Cereal crops / Chemical, physicochemical, biochemical and biological properties / Crop residues / Cropping systems / Dry season / dryland farming / Ecosystems / Field tests / Flooded soils / Fundamental and applied biological sciences. Psychology / General agronomy. Plant production / Irrigated soils / losses from soil / Lowlands / Mineral components. Ionic and exchange properties / Moisture content / Nitrogen, phosphorus, potassium fertilizations / Oryza sativa / Pasture / Phosphorus / Phosphorus fertilization / Physics, chemistry, biochemistry and biology of agricultural and forest soils / plant nutrition / Rainy season / Rainy seasons / Resins / Rice / Rice fields / Rice soils / Rice straw / Sand soils / Sandy soils / Seasons / Sodium hydroxide / soil nutrients / Soil science / Soil water / soil-plant interactions / Soil-plant relationships. Soil fertility. Fertilization. Amendments