The narrow-leafed lupin (Lupinus angustifolius L.) as a nitrogen-fixing rotation crop for cereal production. II. Estimates of fixation by field-grown crops

Abstract

Experiments were commenced in 1978 to evaluate the impact of the narrow-leafed lupin (Lupinus angustifolius L.) on production of subsequent wheat crops in the N-infertile, acidic soils of the Pilliga Scrub region of northern New South Wales. There were four sites. Production of lupin dry matter (shoots, roots) ranged from 5.0 (Florida A) to 11.4 t ha-1 (Kamala), reflecting seasonal rainfall and crop management. Lupin seed yields varied between 1.29 (Florida A) and 2.03 t ha-1 (Kamala); at two of the sites, yields were greater than the yields achieved by the adjacent wheat crops. At Spring Creek, the wheat was not harvested for grain due to the extremely poor plant growth. Seasonal profiles of C2H2 reduction by each of the four lupin crops reflected growth characteristics; maximum activity coincided with rapid accumulation of dry mater. Diurnal profiles of C2H2 reduction were unaffected by plant age. Rates peaked around noon after rapidly increasing from minimum pre-dawn levels. Total N2 fixed by each of the lupin crops was estimated by comparing N Yields of the lupin and wheat crops. The various methods used resulted in almost identical estimates of N2 fixation at Kamala (215-218 kg ha-') and Spring Creek (222-228 kg ha-'). Estimates . of N2 fixed by the two Florida crops ranged from 72 to 101 (Florida A) and from 82 to 134 kg ha-' (Florida B). The data indicate that large amounts of N can be fixed by field-grown lupins, amounts well in excess of the quantities of N harvested in the seed.