Variable Rate Nitrogen Fertilisation of Winter Wheat Based on a Crop Density Sensor

Site-specific nitrogen fertilisation is important in precision agriculture. Based on positive results from a mechanical sensor (pendulum-meter) for the indirect measurement of existing plant mass in cereals, late nitrogen fertilisation in a farm scale strip trial was tested in the growing seasons of the year 2000 in one field and 2001 in two fields. The pendulum-meter was mounted at the front of a tractor. For site-specific fertilising, a tractor-mounted spreader which included an on-board computer was modified. The fertiliser rate was varied according to plant growth. In parts of the plots with low plant mass, the application rate was reduced and in parts with high mass increased. The result of site-specific fertilising was that, for the three fields calcium–ammonium–nitrate (CAN) could be saved in the range of 10–12% without reducing yields. The grain quality was not significantly influenced by low or high fertiliser rates.