Effect of nitrogen fertilization management on mineral nitrogen content in soil and winter wheat productivity

In recent years farmers must use integrated crop growing principles. One of the mostimportant principle isto balance usage of mineral elementsin crop cultivation, especially nitrogenmanagement. Excessive and unbalanced usage of nitrogen fertilizer reduces nitrogen useefficiency and increases nitrate leaching in surface and groundwater. The dynamics of nitrogenforms in soil at different depths and different plant growth stages are studied to increase theproductivity of winter wheat, promoting nitrogen uptake in plants and reducing nitrogen leachingduring the vegetation period. Field experiments were carried out at the Research and TrainingFarm Vecauce of the Latvia University of Life Science and Technologies from 2012 till 2015.Researched factors were nitrogen (N) fertilizer rate: 0 – control, 85, 153, 187, and N ratedetermined by chlorophylmeter (Yara N-tester) 180 (2012/2013), 150 (2013/2014), 205(2014/2015) N kg ha-1, nitrogen and sulphur (S) fertilizer rate – N175+S21 kg ha-1, andconditions of the growing seasons: 2012/2013, 2013/2014 and 2014/2015. The content of nitrate(NO3–N) nitrogen and ammonium (NH4–N) nitrogen was determined in the soil layers 0–20 cm,20–40 cm and 40–60 cm at the growth stages (GS) 30–32, 49–51, 69 and 90–92. All trial yearsthe amount of nitrate nitrogen and ammonium nitrogen in soil decreased during vegetation, butincreased with increasing fertilization dose. Nitrate nitrogen content was significantly influencedby year in 0–40 cm soil layer (P < 0.01) and by nitrogen fertilizer in the 20–40 cm soil layer.Ammonium nitrogen content had significant influence only on nitrogen fertilizer at 20–40 cmsoil layer (P < 0.05). Average grain yields did not show significant correlation with the nitratenitrogen and ammonium nitrogen in different soil layers and plant growth stages, except nitratenitrogen content in soil layer 40–60 cm at GS 30–32 and ammonium nitrogen content in soil layer40–60 cm at GS 69 and GS 90–92.