Legumes as suppliers of nitrogen to pasture

Abstract

Nitrogen losses ranging between 0,16 and 0,26 kg/ha/day may occur direct from the soil of grazed legume pastures wliile removal of animal products from the system represents a major loss of N from the system in the form of protein. On a global basis it has been estimated that annually 200 million tons of N are fixed abiologically (e.g. by lightning) whereas 175 million tons are fixed biologically. Estimates for the fixation of N by clover in a grass/clover mixture range from 100 to 200 kg N/ha/year. Under certain specific circumstances N fertilisation of legume/grass pastures may be advantageous but generally nodule formation and N fixation is depressed by N fertilisation. In many cases failure of legumes to perform adequately in pastures has been due to poor inoculants but strict quality control now ensures the availability of more reliable inoculants in South Africa.

Uittreksel

Verliese aan stukstof tussen 0,16 en 0,26 kg/ha/dag kan direk uit die grond van geweide peulgewas weiding voorkom, terwyl die verwydering van diere produkte uit die sisteem ‘n groot verlies aan stukstof, in die vorm van proteine, ver‐teenwoordig. Op ‘n wêreld basis word dit beraam dat 200 miljoen ton stikstof jaarliks nie biologies (bv. weerlig) gebind word, terwyl 175 miljoen ton biologies gebind word. Na beraming word daar tussen 100 tot 200 kg N/ha/jaar deur klawer in ‘n gras/klawer mengsel gebind. Onder sekere spesifieke omstandighede sal in stukstof bemesting van peulgewas/gras weiding voordelig wees maar normaalweg word wortelknoppiesvorming en stikstofbinding deur stikstof bemesting onderdruk. In baie gevalle is die mislukking van peulgewasse in ‘n weiding toe te skryf aan swak entstof, maar in Suid Afrika word die kwaliteit van die beskikbare entstof streng gekontroleer.