Considerations on the sustainability and environmental impact of intensive pastures

Abstract

Intensive pastures form an important component of livestock production systems in South Africa. The sustainability and environmental impact of intensive pastures via their effects on soil properties and nutrient fluxes vary considerably depending on the systems adopted. Soil organic C and N data from various pasture systems provide evidence of a rapid decline in organic matter levels under annual pastures, particularly on coarse or medium‐textured soils. This evidence, coupled with the vulnerability of annual pastures to soil erosion during establishment, places their sustainability at risk. Soil acidification, accelerated by the use of nitrogenous fertilizers, must be counteracted by liming to ensure the sustainability of pasture systems. Phosphorus and K, both relatively immobile in pasture top soils, are not susceptible to much loss. Nitrogen, on the other hand, is susceptible to both gaseous and leaching losses. Balanced fertilization may limit N losses and soil acidification by ensuring more efficient plant utilization of this element. Research priorities indicated are the development of systems that enhance the sustainability of annual pastures, and the improvement of the efficiency of soil and fertilizer N usage in both annual and perennial intensive pastures.

Intensiewe weidings vorm ‘n belangrike komponent van diereproduksie‐sisteme in Suid‐Afrika. Die sisteem wat aan‐vaar word bepaal of intensiewe weidings volgehou kan word en wat hul omgewingsimpak is na hul effek op grond‐eienskappe en voedingstof verandering. Grond organiese C en N data vanaf verskeie weidingsisteme toon dat organie‐se materiaal‐vlakke vinnig afneem onder eenjarige weidings, veral op grof‐ of medium‐tekstuur gronde. Hierdie bewyse, tesame met die erosiekwesbaarheid van eenjarige weidings tydens vestiging, plaas ‘n vraagteken oor of met hulle volgehou kan word. Grondversuring, versnel deur die gebruik van stikstof kunsmis, moet teegewerk word deur bekalking om volgehoue produksie te verseker. Fosfor en K, beide relatief onbeweeglik in weiding bogronde, is nie aan groot verliese onderworpe nie. Stikstof, daarenteen, is blootgestel aan beide gas‐ en logingsverliese. Gebalanseerde bemesting mag N‐verliese en grondversuring beperk deur meer effektiewe plantbenutting van die element te verseker. Navorsingsprioriteite wat aangedui word is die ontwikkeling van sisteme wat die haalbaarheid van volgehoue eenjarige weidings vergroot, en die doeltreffendheid van grond en kunsmis N gebruik in beide een‐ en meerjarige intensiewe weidings verbeter.

Additional index words:

• Erosion
• leaching
• soil acidification
• soil organic matter