To overcome most environmental problems arising from the broadcast application of solid and liquid N fertiliszers, sub-surface placement of solid and liquid fertilizers has been proposed, and long-time research shows that there is no doubt that below surface placement of plant nutrients is most efficient way to improve the fertilizer efficiency and to minimize nutrient losses (ammonia volatilization, surface runoff). Beside the environmentally positive advantages, the subsurface placement of ammonium or ammonium/urea solutions by injection into the soil has been proposed by Sommer (2000) to supply crops in high rate with ammonium instead of nitrate under practical field conditions (known in Germany as the CULTAN cropping system; Controlled Uptake Long-Term Ammonium Nutrition). This can be achieved as the ammonium concentration at the injection spot is toxic for plant roots and soil micro-organism. Consequently, ammonium turnover in the soil is decelerated. Roots create a dense root net around the ammonium hotspots in the soil and can take up the nitrogen as ammonium before it is nitrified. Results from model experiments where total root systems were exposed to one specific inorganic nitrogen form (usually ammonium vs. nitrate) can hardly been used to explain the positive effects of injection fertilization that can be observed under field condition: Most of these growth experiments show highest biomass production and yield formation in systems where the plants are supplied with half of ammonium and nitrate But after injection fertilization, only a small part of the root systems is in contact with the ammonium hotspots (~ 5 %). Under field conditions, injection of ammonium and urea solutions opens the possibility to shift the N nutrition of the crops towards the physiologically ideal ammonium/nitrate ratio. Future investigations are essential to explain the observed positive effects on crop growth after ammonium injection and partly exposure of the root systems to ammonium. Since 2001, the Institute runs field experiments by use of a 6 m fluid fertilizer point injector which has been adapted for 3 m wide experimental plots. Experiments are carried out on the experimental farm of the FAL, or on farm fields with different crops, different liquid N fertilizers and different timing of injection. Additionally, pot experiments are carried out to investigate the effects of ammonium and urea injection on root and shoot morphology and physiology. In field experiments, cereals usually show in about half of the cases positive yield and quality response of point injection fertilization compared to conventional split surface application of fertilizers, while sugar beet yields and qualities are mainly unaffected. Significantly positive effects have been observed for potato yield and quality. Moreover, the nitrate content in vegetable is significantly decreased. Nitrate leaching measurements have shown that leaching can be minimized by 20 to 30 % in intensive cereal and vegetable production systems, and ammonia volatilization is less than 1 % of that from fertilizer surface application. Injection fertilization is recommended in areas where minimum of zero tillage is recommended. Under such conditions, fertilizer nutrients applied on the soil surface are fixed in the first few centimeters of the topsoil (e.g. phosphate). In areas with regular late spring or summer drought, the interest on injection fertilization is steadily increasing, as the effect of surface fertilizers application in dry seasons is highly critical. Additionally, liquid fertilizers have, compared to solids, the huge advantage that they can be modified easily for the demand of specific cropping conditions (e.g. adding micronutrients). Research of the Institute on point injection fertilization will focus to use the lower crop water consumption during ammonium nutrition which is reported from plant physiological studies for practical agriculture.