Successful fertiliser decisions require robust information about a crop’s likely yield potential, background soil nutrients, paddock history, soil type and rainfall patterns.
This year’s good early rains, followed by a mid-late autumn and early winter drought in many areas will impact on the expression of crop nutrient deficiencies at different stages of the growing season, highlighting the need for careful monitoring, diagnosis and treatment.
Nitrogen (N) can be wasted – even on deficient soils – if levels of other macro and micro nutrients, such as potassium (K), phosphorus (P), copper (Cu), sulfur (S) and zinc (Zn), are not adequate.
Tips for optimising fertiliser programs to meet crop micronutrient requirements include:
- Determine any likely nutrient deficiencies at various crop growth stages and plan ahead to tissue test for diagnosis and then treatment
- Use objective information, such as plant tissue analysis from accredited/certified laboratories
- The best window to tissue test cereals suspected of having a nutrient deficiency is between the start of tillering (about four weeks after sowing) and early jointing (about 12 weeks after sowing)
- Use the same test method/supplier consistently across paddocks and across years to build a database and enable valid comparisons of soil nutrient levels.
Monitoring and diagnosing deficiencies
Target micronutrients for WA grain production are Cu, Zn, manganese (Mn) and molybdenum (Mo).
Through the GRDC’s More Profit from Crop Nutrition (MPCN) project, Department of Agriculture and Food (DAFWA) researcher Ross Brennan has recently updated the MyCrop website information to assist with diagnosing deficiencies of these micronutrients. This can be found on the DAFWA website.
It also outlines the recommended minimum plant micronutrient levels for cereal, pulse and canola crops at various growth stages.
Ross stresses the importance of tissue testing to monitor crop growth and performance, in light of potential yield losses if there are undiagnosed micronutrient deficiencies when crop symptoms are not obvious.
With micronutrients, it is often the case that a deficiency observed in-season through tissue tests may not be completely rectified in the same season.
Current research indicates that about 10% yield losses can occur, even when foliar sprays are used in-season, where tissue tests have indicated deficient levels in plants.
However, plant testing is an invaluable tool to guide micronutrient applications the following year, particularly if the following crop is sensitive to micronutrient deficiencies.
Even if soil tests at other times of the year show adequate levels of micronutrients, there is no guarantee a crop will able to access these elements during key times of the growing season.
This will depend on rainfall patterns, the soil moisture profile and other factors affecting rooting depth - such as subsoil constraints.
Other useful resources outlining micronutrient sampling guidelines and critical levels to help with deficiency diagnosis, analysis and decision-making include:
Treating micronutrient deficiencies
Dr Brennan says foliar sprays and liquid micronutrients are highly effective during the growing season to correct any micronutrient deficiencies and the best bet is the least expensive source per unit of micronutrient.
He says foliar application of Cu and Zn is an emergency procedure when deficiency in cereals has been observed by visual symptoms and/or diagnosed by means of tissue testing.
This could be supplemented by a follow-up soil application before next season.
Potassium (K) - helping crops under stress
Potassium is central to many crop physiological processes, including water relations, sodium uptake and photosynthesis.
Through MPCN, researchers from Murdoch University and DAFWA are investigating whether improving K status can, therefore, increase the resilience of crops exposed to drought, frost and salinity.
Recently released results from trials in 2011 and 2012 highlight that K applied early in the growing season on K-deficient soils can lift wheat yields in crops suffering early drought conditions.
Led by Murdoch University researcher Professor Richard Bell, these trials were set up at Dowerin, Bolgart and Borden on sites with soil Colwell-K levels less than 40mg/kg in the 0-30cm soil profile (levels considered to be K deficient for wheat).
Significantly higher uptake of K, dry matter production and wheat grain yield occurred at the Dowerin site in 2011 - with K fertiliser added - when a long dry spell occurred from stem elongation to grain development.
This was in contrast to a lack of grain yield response to extra K in 2011 at trial sites in Bolgart and Borden (where rain fell regularly during the growing season).
Prof Bell says the application of K at seeding or five weeks after seeding at the Dowerin site in 2011 increased wheat grain yields – with little difference between rates of 20, 40 or 80kg/ha – but the yield improvement was less with late applications of K at 10 or 15 weeks after sowing.
At Dowerin, there was further yield improvement when K was applied with 100kg/ha of gypsum five weeks after sowing.
The lack of yield response to K rate and timing at the Bolgart and Borden sites in 2011 was attributed to a continuously moist soil profile during the year, allowing for better root uptake of K.
Prof Bell says the trial results highlight the importance of testing to a depth of 30cm when soils are at levels considered to be K deficient for cereals to improve predictions of crop response from adding K.
The results also showed the importance of the crop having early access to K in dry years.
Results from this research were presented at recent K seminars held in Northam, Katanning and Albany, supported by GRDC and the Belgium-based Sulfate of Potash Information Board.
More information about K wheat nutrition and fertiliser is available in the GRDC’s Wheat GrowNote
Liam Ryan, MPCN & DAFWA
0401 503 143
Ross Brennan, MPCN & DAFWA
08 9892 8474
Professor Richard Bell, Murdoch University
Melissa Williams, Cox Inall Communications
042 888 4414
GRDC Project Code
DAW00222, DAW00239, UMU00042, UMU00045, UQ00063, DAN00168