The contribution of associative and symbiotic nitrogen fixation to the nitrogen nutrition of non-legumes

Abstract

During the past 10 years estimates of N 2 fixation associated with sugar cane, forage grasses, cereals and actinorhizal plants grown in soil with and without addition of inoculum have been obtained using the 15N isotope dilution technique. These experiments are reviewed in this paper with the aim of determining the proportional and absolute contribution of N z fixation to the N nutrition of nonlegumes, and its role as a source of N in agriculture. The review also identifies deficiencies in both the totality of data which are currently available and the experimental approaches used to quantify N 2 fixation associated with non-legumes.Field data indicate that associative N 2 fixation can potentially contribute agronomically-significant amounts of N (>30-40 kg N ha-1 y-l) to the N nutrition of plants of importance in tropical agriculture, including sugar cane (Saccharum sp.) and forage grasses (Panicum maximum, Brachiaria sp. and Leptochloa fusca) when grown in uninoculated, N-deficient soils. Marked variations in proportions of plant N derived from the atmosphere have been measured between species or cultivars within species.Limited pot-culture data indicate that rice can benefit naturally from associative N 2 fixation, and that inoculation responses due to N 2 fixation can occur. Wheat can also respond to inoculation but responses do not appear to be due to associative N 2 fixation. 15N dilution studies confirm that substantial amounts of N 2 can be fixed by actinorhizal plants.

Effects of nitrogen: phosphorus supply ratios on nitrogen fixation in agricultural and pastoral ecosystems

“…Inhibitory effects of increasing N availability of N-fixation by associated bacteria have been observed for numerous non-legume plant species, but relatively little is currently known about the other edaphic factors affecting their nitrogenase activity (cf. Chalk 1991).…”

Microbial communities and diazotrophic activity differ in the root‐zone of Alamo and Dacotah switchgrass feedstocks

“…ANF is thought to be a loose form of quid pro quo, whereby energy and carbon fixed by the plant are exchanged for nitrogen fixed by bacterial diazotrophs. ANF has generally been considered a relatively small player in the annual nitrogen economy of temperate grasses; however, in some cases, it may provide up to 35% of nitrogen to agriculturally important nonlegumes and forage grasses, such as Miscanthus, energy cane, and switchgrass (Weier, 1980;Chalk, 1991;Wewalwela, 2014). ANF offers a natural solution to an immediate need for plant-available nitrogen while also reducing the footprint (Smil, 1999a(Smil, ,b, 2002Galloway et al, 2003;Oenema et al, 2009;Sutton et al, 2011a,b) of land applied synthetic chemical fertilizers.…”

Symbiotic nitrogen fixation by legumes in two Chinese grasslands estimated with the 15N dilution technique

“…To test the hypotheses above, we investigated the contribution of symbiotic N 2 -fixation by legumes in the two grasslands using the 15 N isotope dilution technique because of its advantage to measure biological N 2 -fixation by legumes in situ (Chalk 1991;Carranca et al 1999). The principal assumption of the 15 N dilution technique is that the 15 N enrichment of the reference plants accurately reflects the 15 N enrichment of the soil N taken up by legumes.…”