Ground Cover Supplement : GC Supplement - Profit from crop nutrition 2013
7 Western region by Janet Paterson DePARTMeNT OF AGRICulTuRe and Food, Western Australia, research officer Dr Craig Scanlan says most soils across the WA wheatbelt now exceed critical levels for soil phosphorus. “Our modelling work suggests many growers can start to reduce phosphorus inputs without any impact on yields,” Dr Scanlan says. Workshops run using Dr Scanlan’s phosphorus model through the More Profit from Crop Nutrition (MPCN) program in the eastern wheatbelt of WA have resulted in growers having the confidence to lower their phosphorus applications by 20 to 30 per cent. “But it’s important to qualify that any adjustments to phosphorus rates need to be done in relation to soil pH and other production constraints because phosphorus requirements will be higher on acid and non-wetting soils and in areas prone to root disease,” Dr Scanlan says. The addition of lime to increase soil pH has been found to improve crop response to nutrients such as phosphorus (Figure 1). It is the relationship between soil pH and phosphorus availability that is underpinning Dr Scanlan’s research in the second phase of the MPCN program. “We’ve known for a long time that soil pH impacts phosphorus availability but what we want to do now is develop practical guidelines to enable growers to make the most profitable fertiliser and liming decisions on acid cropping soils.” The project will quantify the impact of soil pH on critical phosphorus levels, from which updated fertiliser guidelines will be developed. The new guidelines will be delivered to growers via a paddock-based extension program. sOIl ph lImItIng CrOp YIeld While most cropping paddocks in the western region have sufficient phosphorus levels, more than three-quarters have surface pH levels that affect grain yield potential. A large number have a subsoil pH below the critical level of 4.8. “Once surface soil pH drops below 5.5, soil test saves on Fertiliser dollars With soil tests indicating ample phosphorus availability across his north-east wheatbelt property, Western Australian grower Stuart McAlpine decided to lower his 2012 phosphorus application rate to a minimal amount of 1.6 kilograms per hectare. “The decision increased our profits by about $25/ha,” Mr McAlpine says. “Below-average rainfall across the eastern WA wheatbelt in recent years stimulated us to examine ways to lower our input costs and lift profits.” Colwell-P values on the McAlpines’ deep yellow sands indicated they exceeded critical values for near maximum wheat production. “We harvested 2.5 tonnes of wheat per hectare with 10.8 per cent protein and 0.3 to 0.5 per cent screenings in 2012,” Mr McAlpine says. The wheat harvest was estimated to remove about 7.5kg phosphorus/ha. Taking into account the initial application of 1.6kg phosphorus/ha, Mr McApline calculated they had removed 5.9kg phosphorus/ha of their soil phosphorus reserves. “We will continue to soil test and monitor our phosphorus and pH levels and adjust our inputs accordingly,” he says. soil orGanic carbon and nitroGen Soil organic carbon generates increasing production and environmental benefits through its impact on soil structure and fertility and greenhouse gas emissions. A new More Profit from Crop Nutrition project is examining how an increase in soil organic carbon affects fertiliser nitrogen requirements and nitrous oxide emissions in the north-eastern wheatbelt of Western Australia. University of WA soil scientist Associate Professor Louise Barton is leading the project to determine whether increasing soil carbon alters nitrogen fertiliser requirements for crops and raises the risk of nitrous oxide emissions in cropping systems. The project aims to equip growers across all grain-growing regions with knowledge and strategies to reduce overall nitrogen use and increase fertiliser use efficiency. An automated gas chamber system for measuring nitrous oxide emissions from high and low-carbon-content soils was installed at the research trial site in 2012. The site will be cropped continuously until 2014 and record emissions from a commercial rotation of canola, barley and lupins. Associate Professor Barton will assess whether increasing soil carbon makes a difference to the amount of nitrogen required to produce a crop. The team will then quantify crop yield response to various nitrogen rates so that an optimum nitrogen rate for the specific year and location can be calculated. phosphorus availability is compromised – even in soils with more than the critical level of phosphorus,” Dr Scanlan says. The problem is that fixing acid soils is relatively expensive – especially for growers in the eastern WA wheatbelt who operate under very tight profit margins. Dr Scanlan says one solution could be for growers to divert money they might have spent on phosphorus applications into targeted liming of acid soils to boost yield potential. □ Grdc research codes daW00223, uWa00156 More information: Dr Craig Scanlan, DAFWA, 08 9368 3333, firstname.lastname@example.org; Associate Professor Louise Barton, UWA, 08 6488 2543, email@example.com “our modelling work suggests many growers can start to reduce phosphorus inputs without any impact on yields.” – DR CRAig SCANLAN Note: ALL pH QUoteD IS MeASUReD IN CALCIUM CHLoRIDe.
GC Supplement - Farm business management 2013
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