Key insights from N rich and poor strips
Tom Batters and his colleagues from AGRIvision Consultants, Swan Hill, Victoria have been using nitrogen-rich test strips (N-rich strips) informally for many years. Last season they took a more formal approach and followed the test strip progress with photos and NDVI images. The strips are a real time, low-cost visual tool to support the usual pre-season nutritional plans, modelling and soil testing. They show how responsive a paddock may be to N applications throughout the year.
A range of strips
During the 2018 winter cropping season, AGRIvision consultants set up strips on about 15 client properties across their network. Locations ranged from Ouyen to Nhill, across to Marnoo and Wycheproof and many locations between. Some strips were planned while others were opportunistically created from mistakes made during operations. The strips ranged from no fertiliser at sowing, top-dressing zero and double rates of N in-crop, high rates of urea prior to or straight after sowing and even small-scale hand spreading of nutrients.
The strips were generally applied as either a zero rate or double rate to the rest of the paddock. For example, in a paddock where 50 kg/ha of urea was applied, a zero strip and a 100 kg/ha strip were put in to compare to the rest of the paddock.
There was below average rainfall during the 2018 growing season across most of the Wimmera and Mallee. This produced mixed results from the strips. The best visual results came from the zero fertiliser strips at sowing. These showed a very clear and obvious difference in the crop growth, as seen in the photo and NDVI image below. But it can be hard to determine which nutrient has driven the change in crop growth, as there is often more than one nutrient in a starter fertiliser package.
In late August 2018, the N-rich strips applied at top-dressing started to show a difference in paddocks. Another rain event to stimulate more growth would have helped make them clearer. Some of the strips applied just prior or just after sowing showed better responses. But they were still not as clear as expected. The lack of rainfall and crop growth throughout the region limited N responses severely.
To help assess and monitor the strips, the AGRIvision consultants used a combination of visual assessment and free NDVI imagery. The NDVI imagery showed effects that may not have been obvious to the human eye. In some cases, they found hidden strips in paddocks where there was a mistake at sowing not initially picked up.
Despite the poor season in 2018, the N-rich strips provided a low cost, simple tool to help the grower and their adviser to make decisions on N. The strips do not, however, replace good management or agronomics. A full N budget and ongoing review should also accompany the N-rich strip process.
The consultants also advise following strips through to harvest, to add yield data from the paddocks. This is essential to get a full understanding of how much the nutrients contributed to yield in each paddock.
Originally published by the GRDC.
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