Grazing cereal and canola crop nutrition

Take home message

• Sample surface soils 0-10cm and deep to a minimum of 60cm 3/4 weeks before planting
• Manage fallows to maximise early crop emergence opportunities
• Early availability to phosphorus is crucial.  Phosphorus deficiency limits wheat grain yield principally by depressing early growth, leaf emergence rate and maximum rate of tiller emergence
• Confirm any suspected in crop macro or micro nutrient deficiency or toxicity with tissue testing

Phosphorus

Apply recommended phosphorus rates based on mg/kg Colwell P and phosphorus buffering index (PBI) from recent or this season’s soil test results and yield expectations for your area. 43% of central NSW soil tests sampled January to June 2018 were less than 35mg/kg Colwell phosphorus. Normally starter fertiliser rates as MAP or DAP are recommended banded with the seed considering seed bed utilisation (SBU)% and soil moisture at planting. Canola is more sensitive than cereals to nitrogen placed with the seed.

When sowing forage cereals and especially canola, it is important to accurately assess planting soil moisture and soil temperature to maximise early emergence and time to first graze. Phosphorus banded with the seed at planting encourages early root development, increasing root area to access soil moisture and soil phosphorous through the growing season.

Table 1. Distribution of results from Colwell P tests conducted for the central NSW region.  From 1897 soil samples, 0-10cm depth.  Results from Nutrient Advantage Laboratories Jan-June 2018

Western Australian field trials showed a trend towards higher critical Colwell P for cereals on canola with PBI>70 (Andreas Neuhaus et al, 2015). When sowing cereals following canola in the rotation, additional phosphorus at planting should be budgeted for.

Remember with phosphorus there is no second chance.

Nitrogen

If deep N soil test results are showing >120kg/ha nitrogen in the profile, or coming out of an early fallowed pasture phase with >30% productive legume component, or following a high biomass grain legume, then no additional nitrogen may be required.

If deep N soil test results are <60kg/ha (and that was 65% of soil samples in 2018), nitrogen is required and rates will be dependent on the starting soil nitrogen levels, paddock history, organic carbon percentage, rainfall and expected grain yield targets. Assume wheat needs to see 40 kg N/ha for every 1 t/ha of grain yield.  Canola needs ~80 kg N/ha. The primary objective when growing forage crops is to maximise dry matter production and efficiently utilise that dry matter.

Table 2. Distribution of results from Deep N tests conducted for the central NSW region.  (769 soil samples,  0-60cm depth).  Results from Nutrient Advantage Laboratories Jan-June 2018

Early nitrogen and time to first graze is the key with nitrogen. Apply nitrogen on low nitrogen paddocks at rates of 35-50kg/ha/N broadcast and incorporated at planting.

Rates of N loss from urea post broadcasting without incorporation through volatilisation can be 5.4-19% on northern soils (Schwenke et al, 2014).

Additional nitrogen can be applied post grazing through the growing season dependent on seasonal conditions. “Lock up time” can also be managed depending on commodity prices, residual biomass targets and seasonal conditions.

Nitrite/nitrate levels in forage may be an issue in both canola and wheat if; the crop is immature, growth has been slow due to frosts, weather has been cold and cloudy or there has been intermittent water logging. Plants will continue to take up and accumulate nitrate during periods of slow growth and most of that plant nitrate is also located in the bottom third of the stalk. Allow cereals and canola to regain leaf area before reintroducing stock if urea has been top-dressed post grazing.

Manage the risk of high nitrate with controlled grazing, including carbohydrate in the diet.  Avoid grazing with hungry stock. Risk is further reduced by grazing actively growing crops.

Potassium

Cropping soils in the central west generally have more than adequate soil potassium levels, with only 8 out of 1930 samples received at Nutrient Advantage Laboratories January to June 2018 below the critical soil potassium level of 60mg/kg available potassium for wheat/canola.

Wheat forage has a high potassium (K) content – about three to four per cent of dry matter – and a very low sodium (Na) content, often less than 0.02 per cent of dry matter. This can result in a very high K:Na ratio in wheat forage, which can reduce absorption of magnesium (Mg) in the gut of livestock and limit liveweight gains.

The high K and low Na contents in the wheat tissue sample from the Incitec Pivot grazing trial at Millvale in 2018, resulted in K:Na ratios in that forage of 460-500.

This compares with an implied required ratio of 5-7. (Dove et.al, 2009). Most current wheat varieties have similar K:Na ratios to this Kittyhawk sample and supplementation with 1:1 Causmag and sodium chloride mix is recommended to improve animal productivity.

Table 3. Nutrients in Kittyhawk wheat tissues, Millvale grazing trial 2018 sampled 6/6/2018

Sulphur

As sulphur is a dynamic nutrient, in that it is a mobile nutrient in soil and additional sulphur can come into the soil pool through mineralisation during the season.  It is recommended to include testing for sulphur when sampling for deep nitrogen. In most areas, soil sulphur levels at depth are more than adequate for cereals. Additional sulphur may be required for canola.

Table 4. Distribution of results from sulphur tests (KCL40S) conducted for the central NSW region.  (1786 soil samples,  0-10cm depth).  Results from Nutrient Advantage Laboratories Jan-June 2018

Trace elements

There have not been any documented responses in dry matter and/or grain yield to trace element application in grazing cereals or grazing canola in the central west. Zinc deficiency has been confirmed with tissue testing in main season wheat plantings on alkaline soils during cold wet conditions. Manganese toxicity is often seen in the leaves of early sown canola when surface soils are warm and dry. Frost damage in cereals is often misdiagnosed as copper deficiency. Confirm any observed symptoms with tissue testing before undertaking any remedial action. Withholding periods will need to observed if foliar application is undertaken.

References

Neuhaus A, Easton J and Walker C (2015) Phosphorus requirements for cereals: what role does crop rotation play?  Proceedings of the 17th ASA Conference, 20 – 24 September 2015, Hobart, Australia

Rodriguez D, Andrade FH and Goudriaan J (1999) Effects of phosphorus nutrition on tiller emergence in wheat. Plant and Soil 209, 283-295

Schwenke GD, Manning M and Haigh BM (2014) Ammonia volatilisation from nitrogen fertilisers surface applied to bare fallows, wheat crops and perennial-grass based pastures on Vertosols, Soil Research, 2014, 52, 805–821

Dove H and McMullen KG (2009) Diet selection, herbage intake and liveweight gain in young sheep grazing dual-purpose wheats and sheep responses to mineral supplements. Animal Production Science, 49

Contact details

Jim Laycock
Incitec Pivot Ltd
Ph: 0427 006 047
Email: jim.laycock@incitecpivot.com.au