Sulphur cycling and its implications on sulphur fertilizer requirements of grazed grassland ecosystems

• Published in: Agriculture, ecosystems & environment Vol. 49; no. 2; pp. 173 - 206
• Main Authors: Nguyen, M.L., Goh, K.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.1994; Elsevier Science
• Subjects: ABONOS SULFURADOS; AGRICULTURE INTENSIVE; Agronomy. Soil science and plant productions; BESOIN NUTRITIONNEL; Biological and medical sciences; CICLO BIOGEOQUIMICO; CYCLE BIOGEOCHIMIQUE; CYCLING; DURABILITE; ECOSISTEMA; ECOSYSTEME; ECOSYSTEMS; ENGRAIS SOUFRE; EXPLOTACION AGRICOLA INTENSIVA; FERTILIDAD DEL SUELO; FERTILITE DU SOL; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; GRASSLANDS; GRAZING; HERBAGE; INTENSIVE FARMING; MODELE; MODELOS; NECESIDADES DE NUTRIENTES; NUTRITIONAL REQUIREMENTS; PASTOREO; PATURAGE; PRADERAS; SOIL FERTILITY; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; SOSTENIBILIDAD; SULPHUR FERTILIZERS; SUSTAINABILITY; Grassland; Sulfur Organic compounds; Browsing; Review; Sulfur cycle; Sulfates; Agroecosystem; Fertilizers; Nutrient requirement; Animal effect; Animal plant relation; Nutrient; Soil plant relation; Sulfur; Grassland soil
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/0167-8809(94)90007-8

The need for assessing sulphur (S) requirements in intensively-managed grassland ecosystems is becoming increasingly important because of the worldwide emphasis on sustaining non-renewable fertilizer resources and reducing atmospheric S emission. This paper reviews major factors affecting S cycling and efficient utilization of S fertilizers and soil S reserves in grazed grasslands. Models used for quantitatively describing S cycling in these ecosystems are also discussed. The review shows that most (95%) of the total soil S in intensively managed grazed grasslands is present as organic S and the remainder is in readily soluble and adsorbed S. Soil organic S that has been accumulated with time in grazed grasslands receiving regular S fertilizer applications can provide a significant amount of S for plant S nutrition. Carbon-bonded S is the major (50–85%) form of soil organic S, owing to the regular return of animal excreta and plant litter. Grazing animals have a major effect on the amount and rate of S cycling as most (87–90%) of S ingested by grazing animals is returned to soils as excreta. Excretal S is either recycled or subjected to leaching losses and transferred to stock camps. Leaching losses are expected to be higher in camp than in non-camp areas as camp soils contain higher soil organic and inorganic S fractions. Likewise more soil organic S is mineralized in camp than non-camp soils. This may provide S exceeding that taken up by plants and hence could lead to substantial S leaching losses in camp areas. This review identifies the lack of quantitative data on: (1) effects of soil microbial activity and plant S uptake on the fate of applied S fertilizers and excretal S in grazed grassland; (2) rates of soil S transformations as influenced by management and seasonal variables; (3) the contribution of soil organic S to plant S uptake and leaching losses in camp and non-camp areas of grazed grasslands. This scarcity of quantitative data is a major constraint in the development of dynamic S cycling models for predicting rates of S cycling and for estimating plant S requirements in grassland ecosystems where S cycling has not attained a steady state. When a steady state exists, mass-balance S models are more reliable than the traditional practice of using only soil or plant S tests for assessing long-term annual plant S rerequirements.