Ground Cover Supplement : GC Supplement - Precision Agriculture 2005
GROUND COVER PRECISION AGRICULTURE 11 information that variable rate application zones can be derived, and that increased paddock profit will come. However, before heading to the full Variable Rate (VRT or VRA) fertiliser path, the zones are used to increase the efficiency of our soil sampling by target- ing the samples at the good and poor per- forming areas. An example of the sort of soil test results obtained from this targeted sampling, for a paddock in WA, is shown in the table on the facing page. The plants did not lie in the biomass image. They have a real problem at site A, the shallow duplex. The paddock looks the same from the surface but a heavy blocky clay at 10 to 20 centimetres is impeding root growth, limiting access to moisture and stopping the plants performing no matter what the season. This is reflected in a high soil phosphorus test of 30 parts per million. The plants have just not been produc- ing enough to use up the fertiliser applied to this poor performing area of the pad- dock. Putting on more is just wasting money and potentially adding to environ- mental problems. In contrast, the high-performing area at site B looks the same, but the extra 40cm of loamy sand and gravel before the roots hit the blocky clay makes all the differ- ence. The plants tell us that this is the highest performing zone, year in year out. They grow so well that they are using up all the phosphorus applied over the past 20 years. The soil phosphorus level of 9ppm is about what exists in these soils when they are first cleared from the bush. What can we do about the blocky clay? Nothing that is economical. Our best option is to back off on nutrient inputs to the poor performing area and increase them to the under-nourished high performing area. This is a classic example of where variable rate technology will pay handsomely. No extra fertiliser cost for this paddock, just spread it differently. Figure 1 is a base map for this paddock for variable rate fertiliser. The blue areas are high performing and relatively nutri- tionally impoverished and will receive more fertiliser. The red areas are poor per- forming and relatively nutritionally rich, and will receive less fertiliser. The final step comes when we test this knowledge with the different rates going across all the zones (see the parallel areas of blue, green and red above). This is the step where we test how our understanding of plant nutrition and plant performance interacts. We then confirm our nutritional mod- els or modify them for these zones, in this paddock on this farm and with this farmer's management practices. This is one example of how simple PA methods can help graingrowers increase both profit and sustainability when crop growth zones are consistent. Where the proportion of the paddock with stable bio- mass or yield zones is small, the potential to forecast yields and to use VRT will be reduced, and it will be a much more com- plex task to uncover the causes of variabil- ity and determine whether and how they can be managed. Developing methods to do this is a major challenge being addressed by the PA research teams. GRDC Precision Agriculture Initiative (SIP09) GRDC Research Code SFX0003 For more information: Ian Maling, 08 9361 0955, email@example.com Figure 1: Silverfox zoning from biomass analysis: blue = high; green = average; red = low; lighter pastel colors are variable through time. 'Applying more fertiliser to poor performing areas can just be a waste of money'
GC Supplement - Nutrient Management 2006
GC Supplement - Grain Storage 2005