Estimating agronomically relevant symbiotic nitrogen fixation in green manure breeding programs

Abstract

Widespread use of legume green manures is limited by a lack of reliable varieties that meet the needs of farmers. Improving symbiotic N fixation (SNF) in open‐pollinated legume species poses a challenge because normal methods used for assessing SNF conflict with breeding practices such as seed production and removing low‐quality sires. We investigated methods for measuring symbiotic N fixation that are compatible with breeding practice for two major legume cover crops: hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.). We collected two nondestructive samples at the early‐flowering stage (Meristem and Wedge) and a sample at seed harvest (Seed). Our objective was to determine which combination of measurements best predicted symbiotic N fixation (% N derived from atmosphere [Ndfa]) and total N content at 50% flowering. Our statistical approach accommodated the problem that target traits and seed measurements cannot be measured in the same individuals. Overall, the Wedge sample provided the best prediction for Ndfa at 50% flowering. The best predictions for total N plant–1 came from combining vigor ratings with aboveground biomass at seed harvest. In addition to specific recommendations for legume cover crop breeding programs, we provide a flexible statistical method for studying relationships between traits that cannot be measured jointly.

Toward plant breeding for multicrop systems

“…Annual cover crops are perhaps the most obvious example, but there are other examples, including species used in hedgerows, companion plants used for pollinator or pest management, or species used as perennial groundcovers between rows of cash crops. We refer to these crops collectively as ecosystem service crops; they may be selected for traits that enhance their environmental benefits, such as increased biomass production (e.g., to enhance weed suppression and soil organic matter contributions) ( 33 ), increased nitrogen fixation ( 34 , 35 ), or even the release of biological nitrification inhibitors in the soil to reduce nitrogen loss ( 36 ). They are also often selected for the timing-related traits important for alternate-season crops ( 35 , 37 , 38 ) and for any other traits that reduce negative impacts on the cash crop.…”

Green Manure as an Alternative for Soil Recovery in a Bauxite Mining Environment in Southeast Brazil

“…Given this complexity, no methodology addresses all these factors and provides a standard nitrogen availability index (Prezotti & Guarçoni, 2013;Figueiredo et al, 2019). In green manure, leguminous species are the main nitrogen fixators through the symbiotic relationship with soil bacteria (Rhizobium and Bradyrhizobium) (Muller et al, 2021).…”

An evolutionary perspective on increasing net benefits to crops from symbiotic microbes

“…Destructive harvests can also preclude comparing early and late data for the same plant. Combining measurements of N concentration and stable isotopes can provide a good proxy for N fixation and total N in whole plants, if combined with a nondestructive measurement of plant size (Muller et al, 2021 ).…”