Influence of some soil and pasture components on the growth of hill country pastures

New Zealand Journal of Agricultural Research

Gillingham

et al. 2009

A decision support tool which integrated a geographic information system (GIS) with decision tree models to predict pasture production and pasture responses to phosphate (P) and nitrogen (N) fertiliser was assessed on two farms with contrasting climate inNew Zealand. Scenarios of rainfall variability and different fertiliser application strategies were also analysed in this assessment. The results indicated that the models performed well in generating reliable predictions of pasture production and fertiliser responses. The integration of the decision tree models with the GIS provides an efficient tool to assess feed availability and to optimise fertiliser application strategies over landscapes at fine (paddock) A09008; Online publication date 4 November 2009 Received 21 January 2009 accepted 12 June 2009 scale with considerations of climate variability and environmental impact. The limitations of this decision support tool and possible improvements are also discussed.

Section: Discussionsupporting

confidence: 73%

Fine‐scale spatial modelling of pasture production and fertiliser responses under variable climate: Assessing a decision support tool in pasture management

Zhang

New Zealand Journal of Agricultural Research

Gillingham

et al. 2009

“…A range of N fertiliser responses of 1Á33 kg DM/ kg N have been reported in hill pastures (Luscombe 1980;Ball & Field 1982;Lambert et al 1986;Clark & Lambert 1989;Gillingham et al 1998;Blennerhassett 2002;Gillingham et al 2007Gillingham et al , 2008a. Factors affecting the magnitude of response include location (Ball & Field 1982;Gillingham et al 2008aGillingham et al , 2008b, fertiliser application rate Gillingham et al 2007Gillingham et al , 2008aGillingham et al , 2008b, season, slope (Ledgard et al 1983;Gillingham et al 1998;Blennerhassett 2002;Gillingham et al 2003), aspect (Blennerhassett 2002;Gillingham et al 2003) and pasture species composition (Ledgard et al 1982;Rumball 1991).…”

Section: Introductionmentioning

confidence: 99%

Simple models of carbon and nitrogen cycling in New Zealand hill country pastures: exploring impacts of intensification on soil C and N pools

Hoogendoorn

Bowatte

New Zealand Journal of Agricultural Research

2011

Concerns about climate change and water quality make it necessary to have a better understanding of the cycling of carbon (C) and nitrogen (N) within landscapes. In New Zealand, pastoral farming on hill country is a major land use, and there is little information available at a landscape level on the cycling of C and N within these systems, particularly the impacts of land use intensification. Published information on the individual components of C and N cycles in hill country pastoral systems was used to construct simple C and N models for two notional hill country paddocks with contrasting amounts of annual net herbage accumulation (NHA). These simple models of C and N cycling were used to explore the potential impacts of intensification on soil C and N pools. The C and N models constructed illustrate that both the C and N cycles in hill country pastoral farming are characterised by large fluxes in and out of the system and relatively small annual accumulations or depletions of their respective soil pools. The mechanisms by which these inward and outward fluxes are generated differ greatly between C and N. Most of the C cycling through the soil/plant/animal system in a year is sourced from the atmosphere through photosynthesis in that same year and the annual quantity of C ingested by grazing animals is only approximately 25% of that fixed annually. In contrast, the annual quantity of N ingested by grazing animals is 300Á400% of that added to the system annually by fixation, and most of this ingested N (!80%) is returned to the soil in animal excreta. This contrasts with B25% of ingested C returned in animal excreta. Grazing animals, with their propensity to exhibit camping behaviour, are therefore much more influential in the spatial redistribution of N than C in hill country pastures. The simple C and N models presented in this paper indicate that while land use intensification results in increased inputs of both C and N to the soil, intensification is also likely to result in increased losses of C and N from the soil pool. Which of these processes dominates in a given situation determines whether intensification will result in an increase or decrease of soil C and N. Based on a simple C model, we postulate that if intensification increases NHA by one unit there is likely to be an increase in soil C unless at the same time increased grazing pressure results in at least a three-unit increase in dry matter eaten/harvested. Keywords: carbon; nitrogen; hill country; grazing; intensification Introduction Two environmental issues of major concern are increasing concentrations of greenhouse gases in the atmosphere and increased concentrations of nitrogen (N) in receiving waters. These are affected by global carbon (C) and N cycles, and soil C and N are major components of these cycles. Hill country farmers are intensifying *Corresponding author. Email: coby.hoogendoorn@agresearch.co.nz Hill country pastoral landscapes occupy a large area of New Zealand, but compared with flat land, relatively little is known of nut...

“…The mechanisms underlying this better N response in August/September are not clear. However, it may be attributed to some or all of the following factors: (1) the combination of favourable temperature and soil moisture during the August/September period encourage fast pasture growth which in turn increase N use efficiency (Abassi et al 2005;Smith et al 2000); (2) plant available N in soil is very low in early spring due to the low rate of N mineralization (Bolan et al 2004), and (3) N leaching during this period is lower than in other seasons due to the rapid plant uptake and immobilisation by soil microbial biomass (Ledgard 1989;Ledgard et al 1983).…”

Section: Discussionmentioning

confidence: 97%

A decision tree approach to modelling nitrogen fertiliser use efficiency in New Zealand pastures

Zhang

2007

Plant Soil

Quantifying nitrogen (N) fertiliser use efficiency (NFUE) in pastoral systems has important implications for fertiliser management from both economic and environmental points of view. The potential of a decision tree approach for modelling NFUE in New Zealand pastures was investigated. The decision tree model suggested that the time of applying N fertiliser was the most important factor influencing NFUE, with August or September (early spring in New Zealand) being the best time of application. The interaction of rainfall and temperature, rainfall, phosphorus (P) fertiliser history, soil Olsen P and slope were other important factors influencing NFUE. The model was validated for 11 of the 16 trials tested with a predictive accuracy of 69%. The mechanisms by which these factors influenced NFUE and the uncertainty associated with the model prediction were discussed. It was concluded that this type of modelling approach can be used to predict NFUE and thereby to assist decisions on when and where to apply N fertiliser in pastures for increasing productivity while reducing the environmental impact.