N2 fixation and its value to soil N increase in lupin, field pea and other legumes in south-eastern Australia

Abstract

N2 fixation and its potential contribution to increasing soil total N were estimated in field-grown crops of lupin and pea in 21 trials at 10 locations in New South Wales and Victoria, during 1984 to 1987. Chickpea, faba bean and annual medic were included at some sites. Across experiments there were differences in annual rainfall (267 to 646 mm), soil N (0.02 to 0.20%), soil pH (CaCl2,4.3 to 8.0) and sowing date (24 April to 16 June). Most experiments were conducted on acidic (pH < 4.8) red-earth, the others on grey-cracking clay or sandy soil, both of higher pH The differing sites, seasons, and sowing time contributed to variation in legume biomass (2.02 to 14.33 t/ha) and total N (45 to 297 kg N/ha), and the amount of N harvested with grain (8 to 153 kg N/ha), which were related.Lupin fixed an average of 65% of total crop N, and pea 61%, but there was considerable variation about these averages (20 to 97%). Significant differences in % N2 fixation between legumes within sites were few. The amount of N2 fixed averaged 98.5 kg N/ha by lupin and 80.5 kg N/ha by pea, varying 26 to 288 kg N/ha and 16 to 177 kg N/ha, respectively. Variation in proportional and total N2 fixation was associated with biomass, soil mineral N, and sowing date. N2 fixation increased with more biomass and declined with higher soil mineral N, and later sowing (lupin). Each additional tonne of dry matter increased fixed N by c. 20 kg N/ha. Differences in amounts of fixed N between legumes within sites were due primarily to biomass differences.N2fixed by lupin contributed an average of 38.2 kg N/ha to soil N, and by pea, 17.9 kg N/ha. The contribution was variable, -41 to 135 kg N/ha (lupin) and -32 to 96 kg N/ha (pea), and correlated with proportional and total N2 fixation. Positive increase to soil total N occurred when lupin fixed at least 50% of its crop N, and pea 65%. This occurred in most crops. Legumes frequently used less of the available soil N than cereals.

Nitrogen contribution of field pea in annual cropping systems. 2. Total nitrogen benefit

“…In landscape studies, Androsoff et al (1995) and concluded that N 2 fixation was controlled primarily at the micro-scale level (<3-m and 1.5-m distance, respectively) rather than at the landscape-scale level, with available soil N and water being controlling factors. Because field pea may have a high NHI, which is similar to, or higher than the %Ndfa, the contribution to the N status of soil will usually be small at best, even when stover is not removed (Senaratne and Hardarson 1988;Evans et al 1989;Jensen 1989). A net depletion of soil N will likely occur if the stover is removed.…”

“…Field pea will have a direct benefit on the soil N status only if the amount of N fixed is greater than the amount of N removed in the seed, i.e., the percentage of plant N derived from the atmosphere (%Ndfa) exceeds the NHI, defined as the proportion of N in the seed relative to total aboveground biomass (seed + stover) N, and provided the stover is not removed from the field. Comparisons of amount of N 2 fixed and seed N harvested, indicate final N balances ranging from -32 to +106 kg N ha -1 for field pea (Evans et al 1989;Maidl et al 1996). Field pea generally fixes about one-half or more of its N requirements (Bremer et al 1988;Cowell et al 1989;Androsoff et al 1995 …”

Weed Suppression and Performance of Grain Legumes Following an Irrigated Rice Crop in Southern Australia

“…However, soil nitrogen (N) supplementation by legume production varies with legume crop, soil mineral N content, sowing time and the growth rate of the plant. Plant biomass has been shown to correlate strongly with plant N release to the ecosystem [41,57]. Using the method of Matthews and Marcellos [40] to estimate the levels of N added to the soil by faba bean, the S1, S2 and S3 sowing dates in the present study are likely to have fixed 200, 180 and 90 kg·N·ha −1 , respectively for faba bean.…”

“…The calculation of potential N fixation by a crop, based on the total dry matter produced in each sowing dates was used with the reported N fixation rate in Australian conditions for faba bean (at a rate of 120 kg·N·ha −1 ) [40] and field pea (N fixation of 100 kg·N·ha −1 ) [41].…”

Potential Breeding for High Nitrogen Fixation in &lt;i&gt;Pisum sativum&lt;/i&gt; L.: Germplasm Phenotypic Characterization and Genetic Investigation

“…This is a critical issue because many countries, both developing and developed, have not fully embraced or taken advantage of BNF potential and are substantially reliant upon fertilizer nitrogen to drive agricultural productivity. Grain legumes fix approximately 20 to 100 kg·N·ha −1 ·yr −1 and use almost the entire amount of fixed nitrogen in grain production [2]. Many USA extension publications tend to credit only 10 to 25 kg·N·ha −1 for previous grain legume crops.…”