LONG-TERM CONSERVATION TILLAGE AND LIQUID DAIRY MANURE EFFECTS ON CORN .1. NITROGEN AVAILABILITY

Limited information exists on the use of dairy manure in conservation tillage systems. Thus, a study was conducted during 1982-90 in southeast Minnesota, USA, to investigate the potential for using liquid dairy manure as an N source for corn (Zea mays L.) production in conservation tillage systems. Tillage treatments were no-tillage (NT) and spring chisel plowing (CP) followed by field cultivation. Anaerobically stored liquid dairy manure was applied annually, biennially (every other year), and triennially (every third year in the CP treatment only) at recommended rates of N for the region. A conventionally fertilized control treatment and a zero-N control treatment were also part of the randomized complete block, split-plot design. Tillage treatments were applied to main plots and source and frequency of N were applied to the subplots. Manure averaged 76 g kg(-1) dry matter and 3.27 g N kg(-1) on wet weight basis. Of the total N, 54% was in the inorganic form. Nitrogen applied as manure annually at 284 kg ha(-1) produced similar corn yield and had similar corn N uptake as fertilized treatment in both tillage treatments. Manure applied biennially produced corn yields and N uptake comparable with the annual manure treatment in the application year, but yield was reduced 20% and N uptake declined by 30% the following year. Grain yield and N uptake in non-application years were greater with CP than NT systems, which was attributed to greater N mineralization of soil organic matter and manure in CP. There was a small advantage with respect to yield and N uptake of manure over the zero-N control treatment in the second year after manure application. This study shows the necessity of accounting for significant residual N between biennial manure applications to avoid excessive N use in environmentally sensitive regions. It also shows that it is necessary to consider tillage effects when estimating the N available from manure sources.