Spatiotemporal distribution of roots in a maize-kura clover living mulch system: Impact of tillage and fertilizer N source

Authors: ALEXANDER, JONATHAN - UNIVERSITY OF MINNESOTA; BAKER, JOHN; Gamble, Joshua; Venterea, Rodney - Rod; Spokas, Kurt

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2022
Publication Date: 3/1/2023
Citation: Alexander, J.R., Baker, J.M., Gamble, J.D., Venterea, R.T., Spokas, K.A. 2023. Spatiotemporal distribution of roots in a maize-kura clover living mulch system: Impact of tillage and fertilizer N source. Soil & Tillage Research. 227(3). Article 105590. https://doi.org/10.1016/j.still.2022.105590.
DOI: https://doi.org/10.1016/j.still.2022.105590

Interpretive Summary: Perennial kura clover living mulch (KCLM) systems provide environmental benefits in annual row crop systems, but it is challenging to manage them in a way that reduces the competitive impact of the clover on the maize while still maintaining the health of the clover. We tested two different tillage methods, and also the possible use of anhydrous ammonia as a nitrogen source, on the supposition that the caustic nature of ammonia combined with tillage might suppress clover root growth in the row. Maize was seeded into a KCLM prepared with either rotary zone tillage (RZT) or shank strip tillage (ST) and fertilized with either ammonium nitrate (NH4NO3) or NH3 banded at 0.20 m depth within the tilled zone. End of season crop yields were collected and the spatial and temporal distributions of aboveground clover biomass, total root biomass, and soil N, were sampled at seven times between tillage and maize maturity. Root biomass samples were analyzed for their 13C isotope signature to determine the relative abundance of clover (C3) and maize (C4) roots. No significant differences in maize yield or clover biomass were found between the various combinations of tillage and N sources, indicating that the simplest management combination (Strip tillage and ammonium nitrate) works as well as the more complicated management system. Results also showed an increase in nitrate in the interrow soil during the season, presumably resulting from clover decomposition, but the root sampling showed that there were very few corn roots in the interrow, suggesting that the maize received little benefit from that nitrate.

Technical Abstract: Interspecies competition is a management problem for maize production in a kura clover living mulch (KCLM). Current recommendations for managing competition in KCLM are effective and reliable, but they present practical issues that are a barrier to producers. It has been suggested that banding anhydrous NH3 in a KCLM, due to its transient caustic impact, should damage clover roots and provide supplemental clover suppression. This, in combination with a less aggressive tillage tool could reduce management costs and promote adoption of KCLM. This experiment aimed to determine the combined effects of tillage intensity and fertilizer source on maize yield and root biomass pools. Maize was seeded into a KCLM prepared with either rotary zone tillage (RZT) or shank strip tillage (ST) and fertilized with either ammonium nitrate (NH4NO3) or NH3 banded at 0.20 m under the tilled zone. End of season crop yields were collected and the spatial and temporal distributions of aboveground clover biomass, total root biomass, and soil N, were sampled at seven times between tillage and the R4 maize physiological growth stage. Root biomass samples were analyzed for their 13C isotope signature to determine the relative abundance of clover (C3) and maize (C4) roots. Results indicated that ST achieved adequate clover suppression and grain yields which did not differ from those achieved using RZT, regardless of fertilizer N source. Fertilizer N source also did not affect the spatial or temporal distribution of above or belowground clover biomass. Finally, decline of clover biomass over the growing season increased soil NO3-N concentrations in the interrow zone, but sampling showed very little maize root biomass in the interrow suggesting that this N was of little benefit to the crop.