A test of five methods using the example of winter-wheat cultivation shows that site-specific nitrogen fertilisation enables more efficient fertilising without adversely affecting yield.
Nitrogen is an important plant nutrient whose use in plant production ensures crop yield and quality. However, the amounts used are often too high. In Switzerland, the annual nitrogen surplus is around 100,000 tonnes. The reduction of this surplus is therefore a focus topic of Swiss agricultural policy.
Adjusting fertiliser application to available nitrogen
Nitrogen loss risk in arable farming is higher when more nitrogen is available than plants can absorb. To optimise nitrogen fertilisation, Agroscope and Grangeneuve tested five site-specific fertilisation methods against controls (‘standard’, ‘zero’ and ‘plus’ fertilisation):
- Nmin method (soil mineral nitrogen content)
- ‘Adjusted N fertilization norm’ (ANFN) method, also termed the ‘estimation method’)
- N-Tester (Plant-leaf chlorophyll content)
- Nitracheck (Plant-sap nitrate content)
- Sensor-based optical method measuring plant nitrogen supply
Winter wheat was cultivated over a two-year period (2019 and 2020) on the experimental fields in Tänikon and Grangeneuve.
Steady yields and good quality
The investigated methods used between -40% and +10% of the amount of nitrogen used in the standard fertilisation protocol. In general, all methods had a higher nitrogen-use efficiency than the ‘plus’ and ‘standard’ fertilisation methods, i.e. grain yields were higher per kg of applied mineral fertiliser. There was no adverse effect on yields. Protein content was usual for the site, and was more strongly affected by the factors site, year and variety than by the different amounts of nitrogen fertiliser applied depending on the method.
Costs and workload vary
The methods tested differ in terms of cost, workload, required knowledge and seasonal application. The least expensive is the ‘Adjusted N fertilization norm’ (ANFN), which is primarily based on the data of the PEP survey. Implementation requires sound agronomic knowledge, however. Incorporating this method into field-calendar and farm-management software would be both useful and feasible.
For the other methods, either laboratory analyses (Nmin method) or more or less expensive devices were used for measurement on the farm. In these cases, regional recommendations (Nmin method) or inter-farm use of the equipment could lower costs.
Low economic incentives
To date, high technical costs as well as meagre economic benefits due to low mineral fertiliser prices have prevented wider use in Swiss agricultural practice. In addition, factors such as a higher time requirement for planning and sampling as well as insufficient knowledge make using the tested methods difficult. Furthermore, site-specific fertilisation is not a component of PEP.
- Site-specific fertilisation in winter-wheat production leads to more efficient use of nitrogen without yield losses and with yields of good quality.
- The methods run the gamut from very inexpensive and simple options such as the adjusted N fertilization norm to expensive sensor-based fertiliser optimisation, which is currently only worthwhile in the case of larger surface areas.
- Site-specific fertilisation can mitigate the trade-off between environmental protection and productivity. At present, however, there are few incentives for its use.
- Various measures such as incorporation into field-calendar and farm-management software or the inter-farm use of equipment could lower the hurdles for using the method.