Soybean relay-cropped with winter camelina reduces biological nitrogen fixation

Authors: Mohammed, Yesuf; MATTHEES, HEATHER - Winfield United; Gesch, Russell - Russ; Weyers, Sharon; ADEM, SEID - Washburn University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2022
Publication Date: 6/4/2022
Citation: Mohammed, Y.A., Matthees, H.L., Gesch, R.W., Weyers, S.L., Adem, S.M. 2022. Soybean relay-cropped with winter camelina reduces biological nitrogen fixation. Agronomy Journal. 114(4):2375-2388. https://doi.org/10.1002/agj2.21142.
DOI: https://doi.org/10.1002/agj2.21142

Interpretive Summary: To avoid a bare winter fallow, winter camelina, an oilseed crop, can be planted in fall following an August spring wheat harvest and grown to maturity for oilseed production the following summer. Further, this system allows for a soybean crop to be "relay" planted in spring into the growing winter camelina. The effects of the two crops growing together on biological N fixation (BNF) in the roots of soybean, productivity, and the contribution of this fixed N to the next crop are unknown. Scientists in Morris evaluated these effects by comparing fertilized and unfertilized winter camelina-soybean relay systems, spring terminated winter camelina cover crop to non-relay monocrop soybean. The results showed that N fixing bacteria were active in both monocrop and relayed soybean. However, the ureide concentration (an indicator of BNF) was greater for monocrop soybean than relayed soybean. Monocrop soybean also had greater grain yield than relayed soybean, and thus provided greater total protein and oil yields than relayed soybean. However, when we added the oil yields of camelina and soybean together, fertilized winter camelina produced greater total (camelina + soybean) oil yield (766 lb/ac) than monocrop soybean (523 lb/ac) thus showing improved system productivity. The low ureide and grain yield of relayed soybean compared with monocrop soybean could be due to winter camelina shading effects. These findings indicate that more research is needed to develop earlier maturing winter camelina genotypes or modify practices such as row spacing to alleviate shading effects. The findings provide much needed information for scientists, extension specialists, consultants and producers interested in understanding and/or improving BNF in winter camelina-soybean relayed system.

Technical Abstract: The contribution of biological nitrogen (N) fixation (BNF) in soybean ([Glycine max (L.) Merrill]) to plant nutrition and its N credit for the next crop is significant. The amount of N fixed via BNF in monocropped soybean is well documented, but it is unknown when soybean is relayed into winter camelina [Camelina sativa (L.) Crantz]. Therefore, BNF in soybean relayed into fertilized (WCFerti) and unfertilized (WCUnfert) winter camelina grown for seed, soybean seeded after winter camelina was terminated as a cover crop (WCCC) were compared with a monocrop soybean (control). The results showed that N-fixing bacteria successfully infected soybean roots and were potentially active in N fixation for all treatments. The average ureide concentration was in the order of control > WCFerti = WCUnfert > WCCC. The control had 64% more ureide with greater nodule count and size (volume and dry weight) than WCCC. Treatments had no effects on soybean grain protein and oil concentrations. However, the control had greater grain, protein, and oil yields than relayed soybean. Fertilized winter camelina resulted in greater total (soybean + camelina) oil yield (859 kg ha-1) than the control (587 kg ha-1). The lower ureide concentration and soybean grain yields in the relayed-system than the control might be due to competition between soybean and camelina for resources including sunlight. Earlier maturing winter camelina genotypes and better row space management to reduce shading and/or more shade tolerant soybean cultivars are possible options to enhance BNF and grain yield in relayed soybean.