Farms & Farm Machinery - - SPECIAL FEATURE: PRECISION AG -

In 2016, a pad­dock of Com­man­der bar­ley near Moree, NSW was as­sessed as hav­ing high-yield po­ten­tial. Nev­er­the­less, at growth stage 30, ar­eas of crop within the pad­dock were seen start­ing to lodge.

Ap­ply­ing a growth reg­u­la­tor to the crop was a good op­tion to re­duce the lodg­ing, but ap­ply­ing the full rate to the en­tire crop was con­sid­ered un­war­ranted and ex­pen­sive at $30/hectare.

Agron­o­mist Brad Don­ald, of B&W Ru­ral Moree, es­ti­mated that ap­ply­ing a growth reg­u­lant to pre­vent lodg­ing in the high crop biomass ar­eas could po­ten­tially in­crease yields by 0.5 tonnes/ha and, with bar­ley worth $200/t, this would gen­er­ate an ad­di­tional $100/ha.

Per­sis­tent cloud cover at the time pre­vented the use of satel­lite nor­malised dif­fer­ence veg­e­ta­tion in­dex (NDVI) im­agery. In­stead, Don­ald gen­er­ated an ap­prox­i­ma­tion NDVI map of the pad­dock us­ing 700 im­ages col­lected us­ing a mod­i­fied Canon S100 cam­era with a near In­frared (NIR)/blue/green lens that fil­ters out the NIR wave­lengths, mounted on an AgEa­gle fixed-wing drone.

The im­ages were stitched to­gether us­ing off­line Agisoft Pho­to­scan soft­ware then geo­ref­er­enced to fit the co­or­di­nates of the 128ha pad­dock.

Ge­o­ref­er­enc­ing is the process of as­sign­ing real-world co­or­di­nates to each pixel of the dig­i­tal im­age. These co­or­di­nates are of­ten ob­tained by col­lect­ing co­or­di­nates with a GPS de­vice for few eas­ily iden­ti­fi­able fea­tures in the im­age. Us­ing these sam­ple co­or­di­nates, or ground con­trol points (GCPs), the im­age is warped to fit the area be­ing sur­veyed.

SMS Ad­vanced Map­ping soft­ware was then used to es­ti­mate the NDVI of each pixel in the com­pos­ite im­age, high­light­ing the high biomass zones (Fig­ure 1), which were the ar­eas of the crop at risk of lodg­ing and amounted to 72ha. Field in­spec­tion con­firmed that the ar­eas of high­est biomass in the pad­dock were also iden­ti­fied on the map as ar­eas with NDVI ≥ 0.43.

From the drone im­age, Don­ald pro­duced the vari­able rate (VR) pre­scrip­tion spray map (Fig­ure 2), which was loaded into the spray unit con­troller and used to ap­ply the growth reg­u­lant.

By vary­ing the water rate of the spray unit, the high biomass zones (green) were sprayed at the full rate of Mod­dus Evo (400 mL/ha) with a water vol­ume of 80 L/ha, and the re­main­der of the pad­dock (red) re­ceived half the rate by low­er­ing the water vol­ume to 40 L/ha.

The re­sult was a re­duc­tion in cost of the prod­uct and in­creased yield due to a re­duc­tion of lodg­ing. Ad­di­tional un-costed, but sig­nif­i­cant, ben­e­fits in this case from the ap­pli­ca­tion of growth reg­u­lant in­cluded ease of har­vest and im­proved stub­ble man­age­ment for the next sea­son.

The ad­van­tages of us­ing a drone in this in­stance were:

• Rapid cap­ture of im­ages, which were un­avail­able from other sources due to cloud cover

• Timely pro­cess­ing of im­ages and crit­i­cal de­ci­sion-mak­ing • Mak­ing ob­ser­va­tions at a time when the pad­dock was un­traf­fi­ca­ble due to wet con­di­tions.

Left: This pad­dock of Com­man­der bar­ley near Moree was sprayed with two dif­fer­ent rates of growth reg­u­lant Mod­dus Evo to avoid yield losses to lodg­ing. A strip down the cen­tre of the pad­dock was left un­sprayed and clearly stands out in this photo, show­ing a much greater level of crop lodg­ing than the rest of the pad­dock.

Above, Fig­ure 1: NDVI-ap­prox­i­ma­tion map gen­er­ated from 700 im­ages taken with a drone-mounted cam­era us­ing an NIR/B/G lens that fil­ters out the NIR wave­lengths to show vari­abil­ity in crop biomass.

Above, Fig­ure 2: Spray ap­pli­ca­tion map show­ing high (80 L/ha, green) and low (40 L/ha, red) ap­pli­ca­tion rate zones.

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