Soil organic matter and the indigenous nitrogen supply of intensive irrigated rice systems in the tropics

• Published in: Plant and soil 1996-05, Vol.182 (2), p.267-278
• Main Authors: Cassman, K.G., Dobermann, A., Sta Cruz, P.C., Gines, G.C., Samson, M.I., Descalsota, J.P., Alcantara, J.M., Dizon, M.A., Olk, D.C.
• Format: Article
• Language: English
• Subjects: absorcion de sustancias nutritivas; absorption de substances nutritives; Acid soils; Agricultural soils; Agrology; Agronomy. Soil science and plant productions; azote; Biological and medical sciences; carbon; carbone; carbono; Chemical, physicochemical, biochemical and biological properties; flooding; Fundamental and applied biological sciences. Psychology; inondation; inundacion; irrigation systems; materia organica; matiere organique; Nitrogen; nitrogeno; nutrient uptake; Organic matter; Organic soils; oryza sativa; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Plants; rendement; rendimiento; reseau d' irrigation; Rice; Rice soils; sistemas de riego; soil; Soil science; Soil water; sol; suelo; Tropical soils; yields
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/BF00029058

Soil organic matter (SOM) has been proposed as an index of N supply in paddy soils although field validations are few. We evaluated the relationship between the indigenous N supply (Ni) of the soil-floodwater system and soil organic carbon (SOC) or total N (Nt) in surface soil of long-term fertility experiments (LTFEs) at 11 sites, in 42 farmer’s fields with similar soil type, and in the same field in ten consecutive rice (Oryza sativa L.) crops. The Ni was estimated by crop N uptake from plots without applied N (No plots) under otherwise favorable growth conditions. There was a tight linear correlation between yields and N uptake in No plots and tremendous variation in both parameters among LTFE sites, farmer’s fields, and in the same field over time. Correlation between Ni and SOC or Nt explained little of this variation. Factors likely to contribute to the poor correlation were: (1) inputs of N from sources other than N mineralization of SOM in surface soil, (2) degree of congruence between soil N supply and crop demand, which is sensitive to soil drying, length of fallow, crop rotation, and residue management, and (3) differences in SOM quality related to intensive cropping in submerged soil. Better understanding of the processes governing the Ni of tropical lowland rice systems would contribute to the development of crop management practices that optimize utilization of indigenous N resources.