FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

Top farmers achieve high profits, partly due to good management of soil water. This fact sheet looks at the ways farmers can manage soil water to improve their profits. Managing Soil Water Improves Farm Profit Key Points Top farmers focus on doing a good job storing soil water, for extra profit. An extra 20mm, • Crop yield is strongly influenced together with the improvement in water use efficiency which occurs with extra soil water, by fallow rainfall storage and soil can go close to doubling crop profit margins. moisture at sowing. This is demonstrated from results of wheat yields, modelled using APSIM, at Biloela and • Farmers can optimise fallow moisture Springsure for soils with 150 and 180mm of plant available water capacity. storage through a combination of good fallow weed control, zero- At Biloela an extra 25mm increased yield by 440kg/ha, which means an extra 20mm tillage and controlled traffic. should result in a yield increase of around 400kg/ha. At Springsure, an extra 22mm of soil • Benchmarks for Water Use Efficiency water increased WUE from 7.8 to 8.7kg/ha/mm and yield by 470kg/ha. (WUE) can be used to estimate yield Profit increases from $27/ha to $114/ha with an extra 25mm at Biloela, and with extra yield for various rainfall, soil and soil water of 0.475t/ha from an extra 22mm at Springsure, profit would rise 118% from $85 to $184/ha. scenarios. • A series of crops, grown in high TABLE 1 IMPROVED SOIL WATER STORAGE BOOSTS CROP YIELD frequency can have low margins and be less profitable than a rotation SOIL PAWC WHEAT PLANTING IN-CROP HARVEST WUE YIELD which includes some long fallow. MM MAY 30 PLANT SOIL WATER JUN - MID-OCT SOIL WATER KG/HA/MM AVERAGE • Adjusting N application is helped 150 Biloela 145 155 20 7.1 1970 by using yield estimates at planting, based on soil moisture and seasonal 180 Biloela 170 155 20 7.9 2410 outlook. Increase 25 18 440 • Huge yield reductions from planting late support investment in machines 150 Springsure 144 152 16 7.8 2160 capable of moisture seeking planting. 180 Springsure 166 152 16 8.7 2630 • Estimates of crop yield can be improved by more accurate Increase 22 21 470 measurements of soil water using an APSIM modelling by G. Mclean, DAFF Qld. 2014 EM38 machine.

TABLE 2 AN EXTRA 20MM OF SOIL WATER CAN DOUBLE WHEAT PROFIT

WHEAT AT BILOELA WHEAT AT SPRINGSURE

AVERAGE YIELD EXTRA 25MM AVERAGE YIELD EXTRA 22MM

Yield (t/ha) 1.97 2.41 2.16 2.63

Gross $/ha @ $240/t 473 578 518 631

Fertiliser, seed, pests 180 192 165 172

Fuel & Repairs 64 64 64 64

Harvest, freight, misc. 80 86 82 89

Labour & machinery 122 122 122 122

Total costs 446 464 433 447

Gross Margin 27 114 85 184

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FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

Fallow Water Storage Yield Estimates Aid Crop yield is strongly influenced by fallow rainfall storage and soil moisture at sowing. Decision Making Fallow efficiency; the amount of water stored in the soil compared to the fallow Estimates of attainable yields are rainfall, is often below 25%. Zero tillage improves moisture storage considerably over important for good decision making. cultivation and controlled traffic farming (CTF) provides further gains by improving the Benchmarks for Water Use Efficiency infiltration of rainfall and further reducing runoff. Surface cover is also important and (WUE) can be used to estimate yield with CTF and good fallow weed control it may be possible to store an extra 20mm of for various rainfall, soil and soil water soil water, and lift fallow efficiency to around 30%. scenarios. Using Orion as an example, rainfall during a summer fallow is 476mm on average, of In Central Qld, soil stored moisture is which around 25%, or 120mm is stored for the next crop. Most soils can store more important and WUE is best calculated as than this and good fallow management may increase this to 30% and the soil water to the yield divided by soil water at planting 140mm. less soil water at harvest, plus in-crop Extra soil water, not only produces more grain, it can improve the water use efficiency rainfall. on the total amount of water used by the crop. An extra 20mm of water at sowing can A deduction for evaporation distorts produce 400kg/ha of wheat and 500kg/ha of sorghum per hectare. the values for WUE. For example the Figure 1: Fallow efficiency of stubble and Figure 2: Reduced runoff with controlled WUE for a 2t/ha crop with 100mm of soil tillage options – Darling Downs 1978-83 traffic (redrawn from Li et al 2001) water and 100mm of in-crop rainfall is 10kg/ha/mm. If 100mm is deducted for evaporation, WUE is 20kg/ha/mm, giving a false impression that WUE is high in dry seasons, when it is actually low. An example of a yield target is 2.77t/ ha for Biloela in Central Queensland, where average soil water at planting time of wheat is 148mm and in-crop rainfall 122mm, of which 18mm remains as harvest soil water. The 2.77t/ha yield of wheat is produced from 252mm at a WUE of 11kg/ha/mm. WUE improves with harvest index (HI), which is the ratio of grain to total above Cover and Zero-tillage improves soil water storage by as much as 10% as shown ground biomass produced by the plant. in Figure 1. Good fallow weed control is the essential. A few days of delay or a few The harvest index increases with yield escape weeds can reduce the store of soil water. and improved accuracy results from using WUE benchmarks which are Controlled traffic further enhances the infiltration of rainfall increases soil stored water. related to the yield potential. There may be less water running from higher to lower areas in a paddock. Very little data is available on the extra water stored with controlled traffic, but one study over At yields around 2t/ha the HI of wheat is four years at Gatton showed a reduction in runoff of 30 to 50mm. (Li et al 2001). See 0.2, but this increases to 0.4 at 4t/ha. As Figure 2. more moisture is available, there is better tiller survival, more heads per hectare, more grains per head and higher grain weights. This impacts on WUE, which for wheat averages around 9kg/mm for yields below 2.5t/ha, 12kg/mm for yields in the range 3 to 4t/ha and 15 for crops above 4t/ha.

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FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

To improve the estimate of attainable yield, the WUE value can Activity Does Not Mean Profitability be adjusted according to the anticipated water supply to the A series of crops, grown in high frequency can have low crop; a combination of soil water and possible rainfall. margins and be less profitable than a rotation with some long fallow. The crop yields shown below are from a Dalby farm in TABLE 3 BENCHMARKS FOR WATER USE EFFICIENCY AT LOW, MEDIUM AND HIGH YIELDS 2013-14, where chickpea was planted in June as a double-crop on limited soil water after a sorghum crop harvested in January. WHEAT LOW MEDIUM HIGH Wheat grown in the following year, after the chickpea, yielded 2.5t/ha compared with 3.7t/ha for other wheat grown on a long Yield Range <2.5t/ha 2.5-4t/ha >4t/ha (16 month) fallow after sorghum. Available water (mm) 150-250 250-350 350+ TABLE 4 MARGINS FROM A DOUBLE-CROP SEQUENCE COMPARED TO A LONG Benchmark WUE 9 12 15 FALLOW

SORGHUM LOW MEDIUM HIGH CHICKPEA WHEAT WHEAT ON CHICKPEA DOUBLE AFTER A LONG DC AT HIGH Yield Range <3t/ha 3-5t/ha >5t/ha CROP CHICKPEA FALLOW PRICE

Available water (mm) 200-300 300-400 400+ Yield (t/ha) 1 2.5 3.7 1

Benchmark WUE 9 12 15 Price 520 250 250 800

CHICKPEA LOW MEDIUM HIGH Gross $/ha 520 625 925 800

Yield Range <1.5t/ha 1.5-2.5t/ha >2.5t/ha Fertiliser: 24 56 70 24

Available water (mm) 150-250 250-350 350+ Seed 40 34 34 40

Benchmark WUE 6.5 8.5 10.5 Fallow sprays 24 48 60 24

Weeds, Pests 72 15 15 72

Fuel & Repairs 42 52 60 42

Harvest costs 55 50 55 55

Freight & Misc. 53 70 88 53

Labour & machinery 84 100 118 84

Total costs 394 425 500 394

Gross Margin 126 200 425 406 The double-crop of chickpea with a yield of 1t/ha following sorghum, followed by wheat yielding 2.5t/ha produced a combined margin of $326/ha. The wheat crop on a long fallow after sorghum with a yield of 3.7t/ha, produced a margin of $425/ha. Price affects the outcome of double cropping and can change the risk profile of planting on limited soil moisture. In the above example, the combined margin from a chickpea double crop, with chickpea at $800/t would be $532/ha compared with one wheat crop on a long fallow of $425/ha. Yield projections, based on soil water and WUE benchmarks should therefore be taken one step further and margins calculated to estimate the financial outcome.

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FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

Practical Use of Yield TABLE 5 SORGHUM NITROGEN AT ORION; DEMAND VARIES WITH SOIL MOISTURE AND SOI

Estimates - Varying the IN-CROP AVERAGE IN-CROP SOIL WATER EXPECTED WUE YIELD ESTIMATE NITROGEN Rate of Nitrogen RAINFALL EXPECTED RAINFALL MM KG/HA/MM T/HA** REQUIRED KG/HA Adjusting N application at planting or SOI <-5* RAINFALL SOI >+5* topping up the N after planting is helped 80 144 9 2.0 34 by using yield estimates at planting, based on soil moisture and seasonal 80 202 11 3.1 53 outlook. 80 253 12 4.0 68 Nitrogen demand calculations can be made using the projected yield and 160 144 12 3.65 62 protein levels. Dividing protein by six provides an estimate of nitrogen. For 160 202 14 5.07 86 example, wheat grain with 12% protein 160 253 15 6.20 105 will have 2% nitrogen or 20kg N/t of grain. If we assume that the nitrogen *SOI is for August and September prior to a Sept 30 sowing, with data from Rainman recycled from crop residue will supply **Water use efficiency rises from 9 to 15 with increasing yield the next crop residue, then the nitrogen required is the amount which will be removed in the grain. Rules of thumb for TABLE 6 NITROGEN REQUIRED BY WHEAT AT ORION, AS YIELD INCREASES WITH SOIL MOISTURE N demand for wheat around 12% protein are 20kg N/t, while grain sorghum at 10% IN-CROP AVERAGE IN-CROP EXPECTED SOIL WATER YIELD ESTIMATE NITROGEN RAINFALL EXPECTED RAINFALL WUE KG/HA/ protein will have a N demand of 17kg N/t. MM T/HA** REQUIRED KG/HA SOI -VE* RAINFALL SOI RISING* MM

80 120 9 1.8 36

120 120 11 2.64 52

160 120 13 3.77 75

200 120 14 4.8 96

*SOI for April and May prior to a May sowing, does not help predict rainfall in Central Queensland according to data from Rainman **Water use efficiency rises from 9 to 15 with increasing yield

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FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

Moisture Seeking Planting Figure 3: Yield of wheat at four sowing times, Narrabri 2014 (redrawn from Graham et al 2015) An important determinant of wheat yield is planting time. The WUE of wheat declines around 0.5kg/ha/mm for each week of delay past the optimum time around mid-May, increasing to 0.8kg/ha/ mm after mid-June. Yield loss from late planting is worst in dry years with a hot finish. If WUE is 12 for wheat at Dalby, planted in mid-May, it will decline to around 8-9kg/mm for wheat planted in early July. Some varieties are not impacted as much by later planting times, but data below shows the decline in yield is similar for two of the main wheat varieties. For EGA Gregory the gross return from a 15th May planting was $1,442/ha, some $292/ ha or 25% up on the return from wheat planted on 12th June and 85% above the gross return of wheat planted on 4th July (Graham et al 2015). This reduction in profit provides a strong incentive to TABLE 7 EFFECT OF PLANTING TIME ON WUE, YIELD AND PROFIT OF WHEAT invest in planter technology which allows DARLING DOWNS NW NSW CENTRAL QLD moisture seeking, several weeks after rain. PLANTED PLANTED PLANTED PLANTED PLANTED PLANTED WHEAT END OF END OF END OF MID MAY MID MAY MID APRIL JUNE JUNE MAY

Average water (mm) 295 295 250 250 275 275

Water use efficiency 12.8 9 11 7.5 11 7

Yield (t/ha) 3.78 2.66 2.75 1.88 3.03 1.93

Gross $/ha ( at $250/t) 944 664 688 469 756 481

Total costs 661 600 476 433 519 463

Gross Margin 283 64 211 35 237 19

Data from Agripath benchmarking

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FACT SHEET MANAGING SOIL WATER TO IMPROVE GRAIN CENTRAL QUEENSLAND PROFITS

Better Monitoring of Soils and Soil Water Estimates of crop yield to make good decisions on such things as crop and variety choice or nitrogen fertiliser rate will be improved by more accurate measurements of soil water. Soil push rods are not accurate because the soil may not be at field capacity all the way to the bottom of the ‘wet’ profile. Capacitance probes measure soil water at one point in a paddock and are not able to provide an estimate of soil water left at harvest time, when the soil is dry and cracked. Soil water can be monitored quickly and easily using EM38 equipment, according to farm manager, Byron Birch of Moree (Birch 2016). The EM38 can take multiple readings across a paddock, and once calibrated for a soil type can provide accurate estimates for soils which are in various degrees of empty to full. EM38 machine measures soil water The cost of an EM38, at around $20,000 is a deterrent, but when we consider most farmers have more than a million dollars of machinery, an EM38 may one day be regarded as one of the cheapest and most useful pieces of machinery. Calibration of an EM38 is described by Huth (2014), who says the EM38 can provide similar accuracy to neutron moisture probes. Storing water in the soil is such an important part of farming in the Northern Grains Region, that farmers should seriously consider improved methods of determining soil moisture. The EM38 may provide a practical answer to that problem.

More Information Simon Fritch, Agripath Pty Ltd: 0428 638 501, [email protected] Useful Resources Birch B., Smart A., and Huth N. 2016. https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2016/02/Accurate-and- efficient-measurement-of-soil-water-in-dryland-systems-with-EM38 Graham R. 2015. Wheat variety response to sowing time. GRDC Grains Research update Goondiwindi. Huth N. 2014 https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2014/07/Rapid-soil-water-monitoring-using-EM38 GRDC Project Code RDP00013

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