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Check soil moisture before applying nitrogen

C r o p p i n g To p d r e s s i n g w h e a t

There are three factors required tomaximise returns from topdressingwheat late:

• Significant plant-available water atthe time of topdressing.

• A high probability of rainfallfollowing topdressing.

• Use a diagnostic tool to identify thecrop's need for additional nitrogen.

A t a g l a n c e

by Tony Good, COWRA, NEW SOUTH WALES

and Charlie Walker,INCITEC PIVOT

Diagnostic tool Pros Cons

Pre-plant deep nitrogen soil analysis Easy to get on paddocks. Uncertainty over season.Where there is a significant nitrogen shortage, it can Significant mineralisation may occur during autumnbe applied pre-sowing or at sowing. under the right conditions.Valuable for checking a paddock before planting for Temptation to sample too early.residual nitrogen following a drought.

In-crop deep nitrogen soil analysis More clarity over season. May be difficult to apply on paddocks.Able to assess autumn mineralisation. Allow for nitrogen in the crop.Plant-available soil moisture measurements available.

Plant sap analysis In the hands of skilled operators, with optimum Inaccurate where only single samples are taken sampling conditions or multiple sample dates, may under adverse conditions.supply accurate predictions. Time-consuming when carried out properly.Quick turnaround. Diagnostic not prognostic.

Plant tissue analysis Enables additional information on other nutrients Interpretive data is specific to the crop growth stage. (for example, zinc and copper). Dry matter assessments needed for best results.

Diagnostic not prognostic.

Tiller density counts Can delay topdressing until canopy has thinned. Crop stage specific.Fast and cheap. Requires another diagnostic tool for reliable information.Complements other diagnostics. Beware of ‘false values’ during dry periods.Reveals other crop production issues (for example, pests and diseases, plant establishment).

Visual assessment Quick and cheap. Often a deficiency will not be visually noticeable until yield potential has been reduced significantly — to as low as 70% of potential.

Source: Charlie Walker, Incitec Pivot.

TABLE 1 Tools for determining if nitrogen is required

Topdressing late can bring the benefit of highergrain protein and lift yields but assess soil moistureand nitrogen needs before topdressing.

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FARMING AHEAD No. 139 August 2003

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(50% of summer rainfall + rainfall of year todate + predicted rainfall) – 110 = growingseason rainfall.

100mm + 200mm + 150mm – 110 =

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Growth Dry Nitrogen Nitrogenstage matter percentage uptake

(kg/ha) (kg/ha)

DC 1.3 150 6 9

DC 2.2 300 5 15

DC 3.0 1000 4 40

Guidelines for nitrogen uptake in wheat for400–500mm rainfall areas.Source: Tony Good, Cowra, NSW, and Charlie Walker, Incitec Pivot.

TABLE 2 Nitrogen uptake

Method 1

Deep nitrogen takenpre-plant

Regular observation

Tiller counts

Decision based on data, soil moisture,rainfall probability

and markets

Method 3

Budget based on off-takeand previous seasondeep nitrogen results

Tissue or SAP(mid-tillering)

Tiller counts


and markets

Method 2

In-crop deep nitrogen (mid-tillering)

Tiller counts


and markets

FIGURE 1 Models for determining late nitrogen strategies


Method 2 will be popular during winter with in-crop soil testing playing a valuable role. Sampling toone metre (or the depth of the wetting front) allows for nitrogen accumulated in the crop.

Soil texture Readily available soil water values (mm/m) for hardy

crops (–8 to –60kPa)

Sand 38

Sandy loam 65

Loam 74

Clay loam 65

Medium clay 57

Heavy clay 41Source: Adapted from K.G. Wetherby, Soil Description Handbook.

TABLE 4 Available soil water (wheat)

Shoot density at decimal code (DC) 3.0 Yield response Protein response 250–350mm zone 350–450 mm zone 450–650mm zone to added nitrogen to added nitrogen

Less than 250/m2 Less than 350/m2 Less than 500/m2 Positive No effect

250–350/m2 350–500/m2 500–700/m2 No effect Positive

More than 350/m2 More than 500/m2 More than 700/m2 Negative Highly positive*

* Ensure adequate moisture is available.

Note: the table is for mid-season varieties sown on break crop stubble and provided with adequateother nutrients. Source: John Angus, CSIRO.

TABLE 3 Expected response to 5kg/ha of topdressed nitrogen


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C r o p p i n g To p d r e s s i n g w h e a t

Wheat grain protein percentage (%)

Yield (t/ha) 9 10 11 12 13 14Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen

remaining required remaining required remaining required remaining required remaining required remaining required

1.0 16 32 18 35 19 40 21 47 23 59 25 71

1.5 24 47 26 53 29 60 32 71 34 88 37 106

2.0 32 63 35 70 39 80 42 94 46 115 49 141

2.5 39 79 44 83 48 100 53 115 57 147 61 176

3.0 47 95 53 105 58 120 63 141 68 176 74 212

3.5 55 111 61 125 68 140 74 165 80 206 86 247

4.0 63 128 70 140 77 160 84 188 91 235 98 282

4.5 71 142 79 158 87 180 95 212 103 265 111 317

5.0 79 158 88 175 97 201 105 236 114 294 123 353

5.5 87 174 96 193 106 221 116 259 125 323 135 388

6.0 95 189 105 211 116 241 126 283 137 353 147 423

6.5 10. 205 114 228 125 261 137 306 148 382 160 458

7.0 111 221 123 246 135 281 147 330 160 412 172 494

7.5 118 237 132 263 145 301 158 353 171 441 184 529

8.0 126 253 140 281 154 321 168 377 182 471 196 564Source: Derived from nitrogen research trials in NSW, Incitec and NSW Agriculture, 1966–1991.

TABLE 5 Nitrogen required to produce certain wheat yields and protein percentages

Decimal code (DC) to 1.3 Ensure crop has 70% of predicted requirements for the (planting to three-leaf) target yield.

DC3.0–3.1 (fully tillered to first node) Tiller counts: 1. If below target, top-up immediately. 2. If on target, hold. 3. Above — no further action.

DC4.1 (flag leaf present, boot stage) Last chance for yield gain in average seasons. Top up to hold low tiller numbers. Contributions can be made to protein.

DC6.1–6.5 (early- to mid-flower) Opportunity to boost protein (and occasionally) yield in above average rainfall seasons.


TABLE 6 Critical stages for nitrogen in cereals

Zero 50kg/ha of 100kg/ha of 50kg/ha ofnitrogen nitrogen nitrogen

mid-row banded mid-row banded mid-row banded at planting at planting + 50kg/ha

nitrogen DC3.2

Yield (t/ha) and protein(%) 4.10 (10.2) 6.08 (11.1) 6.57 (12.9) —

50kg/ha nitrogen (urea) on October 1 6.65 (11.5) 7.11 (12.9) — 6.04 (13.9)

50kg/ha nitrogen (nitram) on October 1 5.95 (12.3) 7.48 (12.7) — —

* Nitrogen was measured at Ariah Park, NSW, during 1995 on Janz at 235 kilograms of nitrogen per hectareapplied in a deep bulge. Source: Charlie Walker, Incitec Pivot.

TABLE 7 Response to nitrogen timing (profile mineral nitrogen at 235kg/ha)


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Nitrogen application Zero 50kg/ha nitrogen 100kg/ha nitrogenmid-row banded mid-row banded

at planting at planting

Yield (t/ha) and protein (%) 5.72 (12.9) 6.6 (13.3) 5.68 (13.2)

50kg/ha nitrogen (urea) on October 24 6.3 (13.5) 5.7 (13.7) —

50kg/ha nitrogen (nitram) on October 1 6.8 (13.5) 5.9 (13.8) —

* Nitrogen was measured at Wallendbeen, NSW, during 1995 on Janz at 250 kilograms of nitrogen perhectare applied evenly through the profile 0–600mm. Source: Charlie Walker, Incitec Pivot.

TABLE 8 Response to nitrogen timing (profile mineral nitrogen at 250kg/ha)

‘Stolen’ return on investment calculator

Multi-V Base rate 225$/t

Nominal protein 12% Discount 206$/t

Target protein 14% Premium 233$/t

Difference = 27$/t

Target yield 5t/ha

Likely yield increase 0.5t/ha

Protein increase (target) 2%

Nominal nitrogen efficiency 30 (range 0–80%)

Additional nitrogen required 29kg/ha

As urea As nitram

Nitrogen cost ($/kg) 1.1 (by air) 1.6 (by air)

Cost per hectare $32 $47

Product rate 65kg/ha 88kg/ha

Nett return/ha $219 $205

Return on investment 7:1 4:1Source: Charlie Walker, Incitec Pivot.

TABLE 9 Estimating the cost of applied nitrogen and return on investment

About the authorsTony Good farms at Cowra, NSW, and formerly workedas an agronomy consultant. Charlie Walker is anagronomist with Incitec Pivot. Contact Tony Good on:

Email: [email protected]: (0427) 429 241, Fax: (02) 6342 9250.


� Reduce root diseases and nematodesby growing wheat after a breakcrop,winter-cleaned pasture or early fallow.At least 18 months grass-free isrequired to starve crown rot. Test fornematodes and take-all.

� Drought is not a break crop.

� Select paddocks with above averagefertility, considering fallow, previouscrop and its fate, time of lucerneremoval and in-fallow rainfall.

� Reduce weeds by ensuring herbicide-resistant weeds do not set seed in theprevious season.

� Control summer weeds, which reducemoisture, increase disease and delaysowing. Do not miss the second orthird fallow spray in wet summers.

� Avoid areas that waterlog. Applygypsum and use beds or drains.

� Avoid paddocks with subsoilconstraints such as salinity, borontoxicity, dense B-horizons, acid-chokesor hard pans. Carry out soil tests.

� Where possible fix soil constraints. Donot lime and grow wheat in the sameyear as the risk of take-all skyrockets.

� Cultivate before sowing or below theseed at planting on hard settingRhizoctonia-prone soil.

� Select quality seed of locally adaptedPrime Hard varieties. Plant selectedvarieties in their timing window withadequate phosphorus, sulfur, zinc andother trace elements required.

� Apply nitrogen in bands before or atsowing using a rate determined bydeep nitrogen testing and nutrientbudgets for 11 per cent protein.

� Monitor plant density, pests anddiseases. Control weeds and insects.

� Monitor shoot density and check itagainst targets.

� Measure soil water with push probe.Monitor long-term weather forecasts.

� Carry out cost–return budgets.

� Consider the risk of lodging andseptoria. Apply growth regulators andflag-leaf protecting fungicides if needed.

� Calculate additional crop nitrogenneeds on the basis of boosting proteinto 13%+. Use urea on acid soils andammonium nitrate on neutral toalkaline soils.

� Only topdress late (up to flowering) ifthe soil moisture profile is full andfollow-up rainfall is expected.

� Harvest wheat before canola if it ripens first.

� Remember industry obligations andonly deliver quality grain.

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