Report Synopsis

Variable Rate Fertiliser Use in the Livestock Sector

Jack England

Precision agriculture and VRT have been applied in cropping and horticultural industries to maximise plant biomass and quality parameters for many years, but are not yet widespread across pasture and livestock systems. There is little doubt that benefits exist for nutrient use and pasture growth efficiencies by deploying PA and VR tools in grazing systems (Trotter, 2010). Where header yield monitors provide a simple cost/benefit measure of applied PA and VR techniques in the cropping sector, analytic tools and advances in spatial monitoring are now enabling the livestock sector to follow suit.

The challenge for farmers worldwide is best summed up by the “cost price squeeze” concept where the price of inputs is ever increasing disproportionately to the price received for commodities sold. Arguably there is little farmers can do to influence prices received but there is a lot that can be done on the cost side of the equation. One of the largest overheads for a livestock business is the fertiliser bill. Yet despite fertiliser’s finite resource status and extrapolation of future price increases based on historic price trends, it is generally applied in a grossly inefficient manner where agronomic potential is left unrealised. Little has been done to investigate the spatial variability of soil nutrients in grazing systems and even less in quantifying the benefits of making management decisions aimed at taking advantage of this variability.

Visiting livestock farmers throughout the world revealed a dramatic knowledge gap on Variable Rate Technology (VRT), Precision Agriculture (PA) and the finer points of soil fertility and associated profit drivers. Livestock managers need to ensure that the current pasture base is being utilised for optimal profitability and sustainability. In most cases this requires matching peak seasonal stocking rate with peak pasture growth rates. Livestock production depends on yield, quality, pasture utilisation and feed conversion, all factors that are a challenge to measure.

The efficiency with which graziers’ harvest or utilise pastures grown is often indicative of gross margins achieved. Diagnostic soil testing can be better targeted to understand both high and low yielding zones to identify both physical and nutrient constraints to be addressed (McLaughlin et al, 1999). Pasture biomass measurements record only what is in the paddock but not what has been eaten by livestock or left behind as seasonal organic matter carryover. There is a need for pasture yield maps at a sub-paddock scale that quantify actual pasture productivity that consider animal intake and nutrient re-distribution. Recent developments in global positioning system (GPS) collars attached to livestock have helped to overcome these challenges.

Developing a variable rate fertiliser program for livestock systems requires the use of multiple technologies to avoid conflicting scenarios. For instance, obtaining an NDVI (Normalised difference vegetation index) pasture yield map of a paddock after sheep were removed and prior to their return would logically provide insights into which areas were the most productive, thereby validating an increase in nutrient replacement. This technique is valid to a certain degree but misses the opportunity to increase yields in lower NDVI zones that have not received adequate fertiliser to suit agronomic potential. Preferential over-grazing and subsequent growth suppression of zone specific pasture species that were either more nutritious, palatable, or both, is another missed opportunity that NDVI measurements alone cannot detect. Integration of NDVI, soil fertility testing and electro-magnetic surveys, together with understanding the spatial utilization of pastures by livestock, will assist farmers to have a far better understanding of the flux of nutrients across a landscape. This can then be used to formulate a variable rate input strategy (Trotter, 2010). For the sake of making better use of our resources, we can also minimise inadvertent off-site nutrient contamination that damages the environment. Growing more with less is an obvious progression and evolution for farmers.

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