1 September 1995

Germans work to make yield maps worthwhile

By Andy Collings

ATTRACTIVE as it might be, a yield map is worthless unless the information can be interpreted and used to increase profits.

Research by Hydro Agri at its Dulmen centre in Germany may now be providing some pointers – albeit with straight nitrogen only.

Field trials on a 7000ha (17,500-acre) farm at Golzow – 50 miles north-east of Berlin – are claimed to have achieved a yield lift of 0.3t/ha (0.12t/acre) from 16kg/ha (13 units/acre) less nitrogen. That represents a financial gain of about £36/ha (£14.50/acre).

The winter wheat fields at Golzow allowed large-scale tests, one site measuring 37ha (92 acres) and the other 30ha (75 acres). The previous crop was sunflower on soils described as loamy sand and loamy clay.

Yield mapping equipment, office computers and an Amazone fertiliser spreader with a GPS, variable application rate system were under the control of Peter Jurschik of Germanys Institute of Agricultural Engineering.

The first step was to assess the nitrogen needs of the first application. This was done by constructing an "N" map based on the results of soil sampling to assess available nitrogen, plant density checks and estimates of yield according to soil type, prior yield mapping and available soil moisture.

Fields were split into 36m strips. Alternate strips received standard applications of 70, 36 and 42kg/ha splits to provide a total top dressing of 148kg/ha.

Variable rate strips initially received an average of 61kg/ha. But this varied according to yield potential – areas expected to yield well were given 81-110kg/ha, lower yielding areas 51-80kg/ha and the poorest areas 30-50kg/ha.

Second and third nitrogen applications were made according to information on plant need collected using the Hydro-N-Tester chlorophyll meter. A chart is used to convert values into recommended application rates.

Overall, the variable areas received a total of 132kg/ha, 16kg less than the control strips.

The trials appear to have succeeded in matching applications to the needs of specific areas, so allowing better nitrogen use. The 0.3t/ha (0.12t/acre) yield boost on the variable rate strips was accompanied by better grain quality too.

Hydro Agri admits these are the results of only one years trials. More work is to be done and plans are afoot for UK trials.

"It is a small start, but a significant one," says Hydros trials leader Michael Basten. "If GPS technology is to be exploited to the full we have to return to basics like soil testing and plant population counts. Then, and only then, is it possible to formulate plans for site specific plant production."