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 southea st Minnesota, USA, to investigate the potential for using liquid dairy manure as an N source for corn (Zea mays L.) production in conservati on tillage systems. Tillage treatments were no-tillage (NT) and spring chisel plowing (CP) followed by field cultivation. Anaerobically stor ed liquid dairy manure was applied annually, biennially (every other y ear), and triennially (every third year in the CP treatment only) at r ecommended rates of N for the region. A conventionally fertilized cont rol treatment and a zero-N control treatment were also part of the ran domized complete block, split-plot design. Tillage treatments were app lied to main plots and source and frequency of N were applied to the s ubplots. 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. Nitr ogen applied as manure annually at 284 kg ha(-1) produced similar corn yield and had similar corn N uptake as fertilized treatment in both t illage treatments. Manure applied biennially produced corn yields and N uptake comparable with the annual manure treatment in the applicatio n year, but yield was reduced 20% and N uptake declined by 30% the fol lowing year. Grain yield and N uptake in non-application years were gr eater with CP than NT systems, which was attributed to greater N miner alization of soil organic matter and manure in CP. There was a small a dvantage with respect to yield and N uptake of manure over the zero-N control treatment in the second year after manure application. This st udy shows the necessity of accounting for significant residual N betwe en biennial manure applications to avoid excessive N use in environmen tally sensitive regions. It also shows that it is necessary to conside r tillage effects when estimating the N available from manure sources.