Soil nitrogen supply from effluent-amended pasture soils for forage maize production

ABSTRACT

Field trials conducted in the Waikato region over three summer seasons (2007–08, 2008–09 and 2009–10) evaluated whether soil nitrogen (N) reserves at sites previously under long-term pasture and with a history of regular farm dairy effluent application were sufficient for maize production with either minimal or no additional N fertiliser inputs. Crop productivity was assessed in the first (six trials) and second (two trials) years following cultivation of pasture. In first year trials there were no productivity differences between no fertiliser control treatments (NF) and treatments receiving an application of starter fertiliser (SF) or starter and side dress fertiliser (SSF). In second year trials the SF treatment maximised yield at one site, but none was required at the other. Crop yields were high across all trials (22.9–31.9 t DM/ha). Results confirmed that in most cases there was adequate soil N to maximise crop productivity without the need for fertiliser inputs. Despite high crop N uptake, soil mineral N levels remained elevated (109–227 kg N/ha) at four sites after cropping, an observation attributed to high rates of mineralisation during the summer. There were few correlations between pre-plant soil tests and the amount of N mineralised at these sites.

KEYWORDS:

• Farm dairy effluent
• land application
• soil fertility
• nitrogen loading
• Zea mays L

Acknowledgments

Funding for field research was provided by the Ministry of Agriculture and Forestry’s Sustainable Farming Fund (SFF), the Foundation for Arable Research, DairyNZ, Waikato Regional Council and Genetic Technologies Ltd through the ‘Using maize to manage dairy shed effluent’ SFF project (07/037). We acknowledge statistical input from Duncan Hedderley (New Zealand Institute for Plant & Food Research Ltd), the support of collaborating farmers, and project leadership from Andrea Pearson and Gabriele Kaufler. This paper was completed as part of the Forages for Reduced Nitrate Leaching (FRNL) programme. The FRNL programme is a partnership between DairyNZ, AgResearch, Plant & Food Research, Lincoln University, the Foundation for Arable Research and Landcare Research with principal funding from the New Zealand Ministry of Business, Innovation and Employment.

Disclosure statement

No potential conflict of interest was reported by the authors.