Winter Rye Cover Crop Biomass Production, Degradation, And N Recycling
Pantoja, J. L.
Sawyer, J. E.
Barker, D. W.
Winter rye (Secale cereale L.) as a cover crop can take up residual inorganic N between annual row crops and therefore be used to help reduce NO3 -–N loss from fields and movement to water systems. However, does the rye N uptake affect N recycling to soil and add to plant available N? The rye carbon:nitrogen (C:N) ratio could also influence N recycling. The objectives of this study were to evaluate rye biomass degradation and N recycling after spring rye termination in a no-till corn (Zea mays L.) - soybean [Glycine max. (L.) Merr.] rotation. A two year experiment (2010-2011) was conducted at four Iowa sites. Treatments included N rate applied to prior year corn (0, 135, and 225 kg N ha-1) and time for rye degradation after rye control. Only time was considered for rye following soybean. Rye was collected from representative plots, put into nylon mesh bags, and placed on the surface of corresponding plots. Bags were collected after 1, 3, 9, and 15 weeks to measure remaining rye biomass dry matter (DM), C, and N. The average rye biomass production and rye N uptake were low and variable across sites and years (average < 2300 kg DM ha-1 and < 45 kg N ha-1, respectively). Rye biomass, C and N consistently decreased across the 15 weeks, with the rate of degradation slower as time progressed. An average 64% of the rye following corn and 60% of the rye following soybean was decomposed after 15 weeks. Nitrogen recycling due to rye biomass decomposition was greater when following soybean (77%) than when following corn (60%), and this is probably due to its lower C:N ratio (14 vs. 20, respectively). Coupled with the low total rye N content, the amount of N released from the rye residue was only 13 and 21 kg N ha-1, respectively following corn and soybean. The low rye N uptake and net N release from rye residue indicates there would be only a small influence on plant available soil N during the growing season or on optimal N fertilization rate for corn.
This is a proceeding from 42nd North Central Extension-Industry Soil Fertility Conference 28 (2012): 96. Posted with permission.