Author:
Peoples M. B.,Baldock J. A.
Abstract
Experimental estimates of amounts of foliage nitrogen (N) fixed in Australian
pastures range from 2 to 284 kg N/ha.year for annual and perennial legumes
growing in temperate and tropical environments. Differences in the amounts of
N2 fixed relate primarily to the legume content and net
productivity of pastures. On average, close to 20–25 kg of shoot N are
fixed for every tonne of legume herbage dry matter produced across a wide
range of environments. Strategies likely to improve the potential for
N2 fixation include: (i) rhizobial inoculation at time
of first sowing a new legume species; (ii) amelioration of nutritional
problems (applications of superphosphate or lime); (iii) manipulation of
pasture composition (herbicide applications to remove grasses in annual
pastures in the year prior to cropping); and (iv) including lucerne to offset
the year-to-year variability in N2 fixation inputs from
annual legumes. However, pasture response to such management treatments and
the subsequent availability of soil mineral N may be modified by livestock
effects on nutrient cycling, pasture productivity and botanical composition.
Conclusions about the relative size of the contributions of fixed N to the N
economies of Australian farming systems depend on whether or not estimates of
fixed N are included for nodulated roots. Thus residual net inputs of fixed N
after each year of a legume-based pasture are generally rated sufficient to
balance the N removed by at least 1 subsequent wheat crop provided estimates
of below-ground N are included in calculations. Pasture type influences the
duration of subsequent rotational benefits and while residual effects on
mineral N are commonly exhausted within 2 years after an annual legume-based
pasture phase, N carry-over following lucerne generally lasts considerably
longer.
Subject
General Agricultural and Biological Sciences
Cited by
164 articles.
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