In situ validation of fungal N translocation to cereal rye mulches under no-till soybean production

Abstract

Background and aims The ability of grass mulches to inhibit weed performance has been linked to their limitations on nitrogen availability to the weeds. Fungal translocation of N from the soil to the surface mulch has been confirmed in laboratories, but this mechanism has not been documented under field conditions. Methods Experiments used 15 N (NH 4 ) 2 SO 4 , 99.7 at.%, which was uniformly injected below the soil surface at a rate of 1 mg 15 N kg −1 soil. Some plots were treated with a fungicide (Captan) every 2 weeks after injection, while others were not treated. Nitrogen transfer was monitored by measuring levels in surface residue, soybean tissue, and extractable soil inorganic N pools.Results Despite the N release from the cereal rye (Secale cereale L.) tissues ranging from 15 to 50 kg N ha, there was a detectable increase in 15 N enrichment of 10-15 % in the cereal rye tissue. Six weeks after injection, tissue from the plots not treated with fungicide contained 36 % more 15 N. ConclusionsThe increased 15 N enrichment in the cereal rye mulch supports laboratory observations that soil inorganic N is translocated into surface mulch via fungal mechanisms. These findings illustrate microbialmediated sinks for nitrogen in cereal rye mulches in no-till soybean production systems.

Establishing the relationship of soil nitrogen immobilization to cereal rye residues in a mulched system

“…Points for each sampled day after planting are offset to reduce overlap throughout the duration of the study, indicating a bidirectional movement of N between soil and surface residues. Similar quantities of 15 N enrichment of cereal rye shoots were reported by Wells et al (2017) under similar experimental conditions. Such movement has been characterized as evidence of direct translocation of soil N by fungal hyphae (Frey et al 2000;Wells et al 2017).…”

“…Similar quantities of 15 N enrichment of cereal rye shoots were reported by Wells et al (2017) under similar experimental conditions. Such movement has been characterized as evidence of direct translocation of soil N by fungal hyphae (Frey et al 2000;Wells et al 2017). In the present study, the quantity of shoot application rate.…”

“…Recent research on N dynamics associated with high biomass cover crop residues has confirmed Ntransfer from soil to aboveground residues, and provides partial confirmation of the hypothesized fungal translocation mechanisms (Frey et al 2000;Wells et al 2017). However, Wells et al (2017) did not establish the optimal rate of cereal rye residue biomass for N immobilization, nor determine if the N immobilization event had a measurable response on escaped weeds in the system.…”

“…However, Wells et al (2017) did not establish the optimal rate of cereal rye residue biomass for N immobilization, nor determine if the N immobilization event had a measurable response on escaped weeds in the system. We hypothesize that increased cereal rye biomass levels will result in greater immobilization of soil N into surface residues, thereby limiting plant-available N throughout the soil profile and increasing N stress in summer annual broadleaf weeds.…”

Trade‐Offs in Cereal Rye Management Strategies Prior to Organically Managed Soybean

“…This immobilization seems to be playing an even larger role in the Roll-down treatment, probably due to the greater amount of biomass and higher C/N ratio of that biomass. Immobilization from crimped cereal rye has also been noted by Clark et al (2017), and by Wells et al (2013Wells et al ( , 2017. Interestingly, Wells et al (2013) suggest that the reduction in plant-available N caused by cereal rye has potential for regulating weeds, with minor reduction in soybean yield.…”