Tillage Effects on Availability of Nitrogen to Corn Following a Winter Green Manure Crop

Field studies were conducted in 1984 through 1986 to investigate the release of inorganic N to corn (Zea mays L.) following a winter annual green manure crop of hairy vetch (Vicia villosa Roth) that had either been plowed down to 22 cm (conventional tillage, CT), or killed and left on the surface (no-till, NT). Soil samples were taken regularly throughout the season at three depths (0–7.5 cm, 7.5–22 cm and 22–45 cm) and analyzed for inorganic N. Crop growth and N uptake, as well as various other plant, soil and environmental parameters were also monitored. First year data (1985) show that soil inorganic N concentration in vetch treatments was higher under CT than NT, and it was more evenly distributed throughout the plow layer. Both corn yields and N uptake, however, were significantly higher in the NT system, probably because of higher soil moisture content in a dry summer. Vetch did not stimulate significant yield increases over 0-N control plots in either tillage system, although there was greater N uptake by corn in vetch treatments. Under NT, 29% of the original N in the above-ground vetch biomass was measured either as soil inorganic N or corn N. Under CT, 56% of the original vetch N was measured. A repeat of the first experiment was conducted in 1986. Again, higher levels of inorganic N occurred under CT than under NT where vetch had been grown. Contrary to the results of 1985, corn yields were significantly higher in CT treatments than NT treatments at all N levels, and both corn yield and N uptake were significantly higher in vetch treatments than control treatments under both tillage systems. Maximum inorganic N levels were measured in late October in 1986, when 22% and 55% of the original vetch N was measured under NT and CT tillage systems, respectively. Contribution from the Dep. of Agronomy, New York State College of Agriculture and Life Sciences, Cornell Univ., as Agronomy Series paper 1635.