Total number of plots = 24Crop: grain sorghum (variety MR Buster)Row spacing: 0.75 mPlant population: 75,000 plants/ha (Target), 68,000 plants/ha (Actual)Treatments: There were 7 treatments = 0, 20, 40, 80, 120, 160, 200 kg N/ha all applied at sowing. Fertiliser used was urea. Application was in a band 0.1 m to the side of the plant row and 0.05 m below the soil surface. Automatic GHG-measuring chambers were situated on treatments 0, 40, 120 and 200 kg N/ha only.The other 3 plots within the overall trial area were used for an N mass balance experiment which had 3 x 15N miniplots within each of the three plots. The three miniplots had three rates of 15N-labelled urea applied (40, 120, 200 kg N/ha)Basal Fertiliser: 180 kg/ha of single superphosphate fertiliser applied in the seed rowSowing: 23/10/2012Flowering: 18/01/2013Harvest: 21/03/2013

In order to equalise the trial area for soil nitrogen (after the previous year had had either legume or cereal plots) we grew an interim crop of barley during 2012 that used up most of the soil nitrate N. This crop was mulched before grain-filling and all aboveground plant material removed from the site. Therefore the soil at sowing had minimal soil nitrate N and was quite N-deficient for the sorghum test crop. As a result of growing the barley “catch-crop” the soil was also very depleted in stored soil water, so prior to sowing the sorghum we watered the trial area thoroughly with a travelling irrigator.

After sowing, very little rain fell in the first month, so between 19th and 21st November 2012, we used a soaker hose to water the plots and enable the struggling crop to establish. Some areas were resown by hand before watering where the intial germination was patchy.