Spatial analysis of nitrogen strip trials in sugarcane

Anthony Webster1, Rob Bramley2

1 CSIRO Agriculture, McGregor Road, Smithfield, Qld, 4878,

2 CSIRO Agriculture, Waite Campus, Urrbrae, SA, 5064


Nitrogen losses from sugarcane farms pose a threat to the Great Barrier Reef. Applying differential rates of nitrogen within blocks is one proposed management practice to reduce this threat by matching nitrogen rates to crop demand at the within-block scale. Farmers need practical methods to determine the appropriate nitrogen rate to apply to differing yielding parts of their blocks when employing variable rate application. We implemented a nitrogen strip trial with rates of 37, 132, and 170 kg N/ha in a plant crop of sugarcane, in comparison to the farmers normal rate of 153 kg N/ha. The block was harvested with a yield monitor fitted harvester. From the resultant yield map, yield values were extracted every three metres along the centre line of each strip. Rolling groups of ten extracted yield values were compared for each test strip to an adjacent area that received the farmer’s normal application via a paired two tail t-test. Yield was found to be significantly different for portions of each test strip and the normal N application rate. This information, used in conjunction with the yield map, was able identify areas of the block where lower application of N could be justified. In different parts of the block each of 37, 132 and 153 kg N/ha would achieve maximum yield. The farmer could use this information to apply lower than normal rates to areas where these lower rates do not compromise yield. Applying N differentially at the within-block scale at rates that match crop demand would be the optimal strategy in this block, and will lead to reduced N losses to the Great Barrier Reef.