Ground Cover North : Ground Cover 073 March-April 2008 - North
Soil tests urged to ensure nutrition is profitable BY NICOLE BAXTER n Cropping experts are urging growers to rethink nutrient management strategies, and soil testing, to make sure the most profitable decisions are made this year. Independent soil and plant nutrition specialist Dr Chris Dowling, from Nutrient Management Systems, is among those who are encouraging more growers to use comprehensive soil tests to avoid paying for fertiliser that might not be necessary. Dr Dowling says fertiliser and grain prices have doubled, but soil-testing costs have stayed at, or close to, 2007 levels, making tests a way to avoid wasting money without risking nutrient deficiencies. He notes that when cashflow is poor, farm business viability is at risk, so a common strategy is to cut fertiliser rates and soil testing, even if this means risking some potential profit. "But an alternative is to focus on the potential profit gain from better nutrient management and to use soil testing to help develop a viable fertiliser strategy for the next three to five years," he says. "Managing inputs on the basis of (existing) soil supply and plant demand, within the framework of a fertiliser budget, is crucial for making fertiliser investments profitable." With regard to phosphorus, MS&A adviser Andrew Speirs, from Casterton in Victoria, encourages a measured approach, rather than reacting to high prices and applying little or no starter fertiliser. He says it is essential to know each paddock's Colwell phosphorus level and understand where this number stands in regard to a likely response to applied phosphorus in grain yield: "In annual crops after sowing, there is no second chance to apply phosphorus." Both advisers recommend developing a strategy that records progress over five to 10 years based on a consistent and well-structured soil-sampling program. Dr Dowling says valid nutrient management strategies might include 'run down', 'play the season' (not possible with phosphorus), 'apply the economic optimum', 'maintenance', 'budget' and 'build up'. He cautions against using broad recommendations based on national, state or regional 'recipes', and suggests more precise fertiliser management tailored to soil type and individual goals. AgNVet agronomist Neil Durning, based at Junee, NSW, agrees: "The days of setting the airseeder at a blanket rate of 100 to 120 kilograms a hectare of monoammonium phosphate for the whole cropping area are over unless you've got a lot of cashflow," he says. If soil testing has not been part of the decision making, both South Australia-based consultant Allan Mayfield and Dr Dowling recommend a 0 to 100 millimetre soil test to develop an improved nutrient plan for most nutrients and nutrient-related conditions. Dr Dowling argues that spending as little as $100 to $200 per paddock on a soil test is a small investment, given the wide swing in potential profit gains and losses caused by the variations that usually exist within paddocks for soil types and yield fluctuations. Where soil phosphorus reserves are known to be adequate and crops are not likely to be responsive, Dr Mayfield says a 'budget' (also known as a nutrient audit) might be enough to judge fertiliser rates according to nutrient removal by previous crops. For cereals, he uses 4kg of phosphorus per tonne of grain; for pulses 6kg a tonne; and for oilseeds 9kg/t of grain. Dr Dowling says soil tests are particularly valuable when records are nonexistent or old and when conditions have changed, making nutrient concentration and location difficult to predict -- such as in a failed crop where hay has been cut or on paddocks where weed growth has been prolific due to summer or autumn rain. A recent national grower survey indicates that just 50 per cent of growers sample their soils to determine how much fertiliser to apply in 25 per cent or more of their paddocks each year, but advisers say the massive jump in fertiliser prices is the signal to make better use of soil testing. Wagga Wagga-based Holmes Sackett consultant John Francis is concerned that production losses will occur if soil testing is excluded from management decisions this season. To demonstrate his point, Mr Francis describes a scenario comparing two growers, Farmer A and Farmer B, who both have a water-limited yield potential of 4t/ha. Farmer A has low soil phosphorus levels (less than 15mg/kg Colwell) but does not know this because he never soil tests. Farmer B has moderate to high soil phosphorus levels (more than 60mg/kg Colwell) and monitors his soil nutrition regularly. Due to financial constraints, Farmer A cuts his normal starter fertiliser rate from 100kg/ha of monoammonium phosphorus (22 per cent phosphorus) to 60kg/ha. Farmer B also cuts his starter fertiliser to the same rate but has been building his soil phosphorus levels over time. The data he has built up also means he only cuts the rate in paddocks with known high soil phosphorus levels. Nutrient management GROUND COVER MARCH -- APRIL 2008 10 Developing a strategic nutrient management plan has become more important this year in the face of large increases in fertiliser costs PRECISION PAYS WITH NUTRIENTS Precision nutrient management has been estimated to deliver yield advantages of $20 to $36 per hectare over blanket applications for some SA and WA locations. Consultant Allan Mayfield says a paddock near Cr ystal Brook, SA, is a useful example of how zone phosphorus management can be used. The paddock has a long histor y of 'blanket' fer tiliser application. Dr Mayfield says six years of yield maps showed consistent yield differences between par ts of the paddock. The paddock was divided into two zones -- high and low yields -- and confirmed with an EM38 sur vey. Soil tests showed the high-yielding zone had a 14 per cent higher plant-available water-holding capacity than the low-yielding zone. Dr Mayfield says the high-yielding zone had 27 milligrams per kilogram of phosphorus (Colwell), while the low-yielding zone had 57mg/kg, reflecting a build up of phosphorus where phosphorus was applied at rates more than removal and tie-up. In both areas, trials were carried out for four years in which phosphorus was applied at 0, 7, 20 and 30kg/ha. The crops grown were wheat, peas, wheat and barley during 2003, 2004, 2005 and 2006 respectively. In the cereal seasons there was no yield response to added phosphorus in the low-yielding/high soil-phosphorus zone, while in the high-yielding/low soil- phosphorus zone there was a yield response in 2003 and 2005 but not in the 2006 drought. Dr Mayfield estimates that if the grower had used the optimal phosphorus rate -- as determined by each year's results -- then the gross margin would have been, on average, $36 a hectare better than the traditional blanket application of 11kg/ha phosphorus. In WA, CSIRO researchers Michael Rober tson and Yvette Oliver simulated the impact on profit of crop yield potential due to season and soil type. Using APSIM software, the researchers simulated estimates of wheat yield potential from the past 30 seasons for a range of soil types at Kellerberrin and Mingenew. The research showed improved estimates of yield potential could increase gross margins by $2 to $20/ha over 'farming for average', with higher yield responses occurring on soils with lower plant-available water capacity. Dr Roberston and Dr Oliver conclude that the biggest gains from zone fer tiliser management can be made in drier locations and on poorer soils. GRDC Research Code CSA00007 More information: Allan Mayfield, 0418 818 569, firstname.lastname@example.org; Yvette Oliver, 08 9333 6469, email@example.com PHOTO: NICOLE BAXTER Soil test: collect the soil core by pushing and twisting the tool until it penetrates the soil to the right depth, usually the footrest. Take a spread of samples between or across rows of the previous crop stubble and avoid sampling directly over the row.
Ground Cover 072 January-February 2008 - North
Ground Cover 074 May-June 2008 - North