New and emerging technology is making the measurement of variations within a paddock more achievable and more affordable. The Gloucester Precision Farming Project is a partnership between Gloucester farmers, Precision Pastures and University of New England to road test new technologies, including the use of drones, electromagnetic induction, satellite imagery, GPS soil testing and GPS cattle movement monitoring. The aim is to provide objective measured data that can contribute to a better understanding of the paddock and the processes that are occurring within a paddock.
Understanding the paddock
In a pasture system there are a range of interrelated factors that influence pasture production, the demand for nutrients and the movement of nutrients around a particular landscape. Measuring the effects of these within a paddock can improve its long term management to get a better return on investment in fertiliser, fencing and water improvements.
Within a paddock, often 80% of production comes from just 20% of the land area. This is known as the Pareto Principle. The deeper soils, flatter areas and places where rainfall drains to the valley floor produce 2-3 times the pasture growth throughout the year than the shallower drier soils.
Key underlying factors that determine potential pasture productivity are the soils ability to capture and store rainfall. This is often termed the PAW plant available water and it is determined by soil depth, soil texture, slope, and aspect and soil density. The greater the PAW of a soil profile, the higher the potential pasture production. PAW may vary within a paddock from 30 mm to 150 mm providing vast differences in potential for growth.
Many of these physical characteristics cannot be changed and provide lasting limitations to pasture growth that need to be recognised. Rather than apply fertiliser at the same rate to the entire paddock apply more to the areas that inherently have greater potential.
Assessing natural soil variability
Soils vary across a landscape according to the way they were formed, either in situ or transferred such as alluvial flats. In their natural state there can be large variations in factors such as soil pH, soil texture and to some extent soil nutrients.
When a soil test is taken as an average for the paddock the real situation can mean there is section of the paddock 50% higher and also 50 % lower than the soil test value. If that soil tests is marginal it can mean 40% of the field is severely deficient, and requires attention where as a marginal test would suggest it’s not a high priority to fertilise with that nutrient. Further the averaged soil test doesn’t tell where those low areas are.
While it is possible to soil test different areas within the paddock the same problem can apply. On the other hand GPS gridded soil samples provide a more detailed picture and can pick up areas of severe deficiency and record the areas accurately. This gives greater confidence to make decisions.
When a paddock has been fertilised for some time the amount of pasture produced increases and with it the amount of nutrient transferred around the paddock increases. So variation in nutrients are often much higher in fertilised paddocks than unfertilised natural state paddocks.
The habits of the grazing cattle can have a large bearing on where nutrients are harvested and then where they are deposited within a paddock.
Cattle tend to graze where feed is abundant and easy to graze. 85-90% of the nutrients ingested are then returned to the paddock, but rarely evenly unless the area is very flat. A proportion of the nutrients harvested by grazing are transferred to places of rest and rumination, near shade trees, watering points and flatter areas within a paddock. Cattle camping behaviour can also be influence by aspect, slope, wind direction and height.
Soil phosphorous and potassium can be a useful indicator of this process showing where grazing is removing and depositing nutrients. Area of high pasture production and high grazing intensity can be very low in phosphorus and potassium, where areas of rest and nutrient deposition can be very high in these nutrients.
Species indicators can also inform where nutrients are being moved. Kikuyu dominance can indicate transfer of nutrient to ridges or flats, and or the presence of greater moisture in valley floors. Carpet grass indicates medium to low fertility and species such as Blady and Whisky Grass, Kangaroo Grass indicated very low fertility and soils with low PAW.
When high growth areas produce 8-10 t/ha/yr of dry matter compared to 2-3 t/ha/yr in low growth zones there is also a need to apply larger amounts of fertiliser to enable high zones to continue produces to potential. If this doesn’t occur the soil fertility will decline and bring pasture growth with it – a common problem found in many fertilised paddocks.
The aim of this project is to help farmers identify the high zones and fertilise them appropriately rather than have a blanket application of nutrients across the paddock. Equally important can be to avoid fertilising areas where there is already a large build-up of nutrients due to cattle camping behaviour.
Other management options include adjusting fencing, rotational grazing, and the location of water and the presence of shade trees to provide more even grazing of the paddock.
For more information contact Peter Beale (02 6551 8994 x239) or Albert Mullen (02 6551 8994 x235) at the Hunter Local Land Services office at Taree.