W.C.A. van Geel

Nitrogen Fertilizer Replacement Value of the Liquid Fraction of Separated Livestock Slurries Applied to Potatoes and Silage Maize

Separation of livestock slurries followed by reverse osmosis yields mineral concentrates (MCs) in which almost all nitrogen (N) is ammonium (NH4)-N. The ability of MCs to substitute calcium ammonium nitrate (CAN), a common conventional mineral N fertilizer, was tested in two trials on a silty loam soil (ware potatoes, 2009 and 2010) and four trials on sandy soils (starch potatoes, 2009 and 2010; silage maize in 2010 and 2011). The N fertilizer replacement value (NFRV) of spring-injected MCs ranged from 72 to 84%, slightly less than their share of ammonium-N (90–100%). The fate of N that was apparently unavailable to crops was not fully disclosed, but there were indications that ammonia loss may have played a role.

From theory to practice: using canopy reflectance to determine sidedress N rate in potatoes

In potatoes in the Netherlands, more than 40 kg N/ha can be saved on average relative to current practice with a canopy reflectance-based N sidedress system. Farmers report several barriers to adoption of the system. The work described here seeks to remove these barriers through additional experiments. The results show that the sidedress system can be used with various cultivars of ware and starch potatoes, on sandy and clay soils. The results further show that the N-Sensor can be used as is and that the CropCircle can be used after modification of its output. Finally, on-farm comparisons show that the canopy reflectance-based N sidedress system consistently results in yields that are at least as good as those obtained in recommended practice and saves N. It is concluded that the canopy reflectance-based N sidedress system is now ready for practical use in potatoes.