Distances are found by measuring the difference in signal travel time between a satellite and receiver by means of accurate, synchronized clocks installed within a satellite and receiver. An unknown earth surface position can be calculated by triangulating the range distance to three or more satellites of known positions. Conventional uniform application leads to over fertilization of the unproductive areas of a field and under fertilization of the more productive areas. Variability in dryland grain yield is largely determined by differences in available soil moisture. Yields tend to be lower in knolls due to low soil moisture versus depressions where yield tends to be higher due to high soil moisture.
Variable application leads to adequate fertilization of the productive areas of a field.
This boosts grain yield and protein in these areas. Local base station method of providing differential GPS in real time via radio link. Farmers now have the capability of measuring crop yield with combines equipped with a GPS receiver and continuous grain yield sensor. Impact-type sensors are available that mount in the clean grain elevator. They measure grain yield by means of a tiny load cell that is sensitive to changes in the mass of grain impacting a plate situated in the grain flow stream inside the elevator.