Underestimated role of legume roots for soil N fertility

Abstract

Nitrogen (N) is a major fertilizing element for plants. The distribution of N in legumes is influencing the efficiency of the next crop. Nitrogen storage in legumes is actually estimated by N fixation in shoots, whereas there is little knowledge on the contribution of roots and nodules to legume N and soil N. Here, we studied the contribution of roots and nodules of grain and pasture legumes to plant N and soil N in Mediterranean fields. Experiments were run under rainfed conditions for a 2-year period in three regions of Portugal. Entire plants including top plant and visible roots and nodules were sampled at the end of the growing seasons for grain legumes, sweet and yellow lupine, and over two harvests in case of pastures. N 2 fixation was measured for grain legumes and pasture legumes using 15 N tracing. Our results show that aboveground N concentration did not vary among legumes, but differed in the belowground tissues. Field studies show that 7-11 % of total legume N was associated with roots and nodules. Data also show an allocation of 11-14 kg N fixed t −1 belowground dry matter in indeterminate legumes, which represents half the amount of total aboveground plant. This finding demonstrates that investigation relying only on shoot N underestimates the role of legumes for soil N fertility.

Nitrogen uptake and transfer in a soybean/maize intercropping system in the karst region of southwest China

“…In the intercropping of legumes with nonlegumes, N fixed by legumes becomes available to nonfixing companion species (Carranca, Torres, & Madeira, ; Moyer‐Henry, Burton, Israel, & Rufty, ). Previous intercrop study demonstrated that 32%–58% of the N assimilated by sorghum was derived from soybean (Chu, Shen, Li, Zhang, & Wang, ; Fujiu et al., ), and these N transfers appeared mostly in different communities between N 2 ‐fixing and non‐N 2 fixing plants (Hamel, Barrantes‐Cartin, Furlan, & Smith,; Chu et al., ; Haby, Stout, Hons, & Leonard, ; Isaac et al., ).…”

“…In the intercropping of legumes with nonlegumes, N fixed by legumes becomes available to nonfixing companion species (Carranca, Torres, & Madeira, 2015;Moyer-Henry, Burton, Israel, & Rufty, 2006).…”

Plant Components of Agroforestry System Have Different Contributions to Soil Fertility

“…For the tree component, the highest N contents are attributed to the contribution of underground tissues for the maintenance of the nutrients in the soil and, consequently, for its fertility (Carranca et al, 2015). There is also contribution of the tree component to the cycling of nutrients through the biological N fixation, for being a leguminous species.…”

Barriers to Agro-Ecological Intensification of Smallholder Upland Farming Systems in Lao PDR

“…The %Ndfa of ricebean in the upper plot was about twice that in the lower plot (Table 5), which can be explained by the more intense competition with maize for P at the lower plot as mentioned above. The low levels of N 2 fixation, combined with the fact that most ricebean residues in farmers' fields were grazed by livestock, means that the transfer of N from atmospheric fixation to the soil is likely to be negligible as N allocation studies have shown that only 5%-11% of the fixed N is found in roots [37,38].…”