The effect of urea and urea with urease inhibitors on tuber yields and starch content in potatoes

Volatile losses of NH₃ originating from urea may be reduced by the application of urease inhibitors. The objective of the work was to compare the effect of three rates of nitrogen applied in two different fertilisers NDASH urea and urea with urease inhibitor (NBPT). The effect of the fertiliser on tuber yields and starch content in potatoes was monitored. Two-year small-plot field experiments were established with the early cultivar 'Red Anna'. The experiment involved seven treatments (with 4 replications), including a control unfertilised treatment. The N rates were as follows: 54, 72 and 90 kg N ha^-1. The yields differed statistically significantly in the respective years, i.e., 29.3-40.5 t ha^-1 in 2010 and 17.3-23.7 t ha^-1 in 2011. The effect of both fertilisers and/or nitrogen rates on tuber yields was irregular. Higher yields were achieved in treatments where higher rates of urea were applied as compared to the same rates of urea with the inhibitor only in 2011. On the other hand treatment with the lowest rate of urea with urease inhibitor showed yields comparable to or higher than all the other treatments in both years. The year-on-year fluctuation in the starch content of the tubers was minimal, i.e., 12.48-15.00% (2010) and 11.79-13.60% (2011). The lowest starch content in tubers was achieved with the lowest rate of N in urea. No differences in the starch content were observed in terms of the N rates applied in urea with the urease inhibitor in the two years. The results showed that the effectiveness of both fertilisers was affected primarily by the year.