On the basis of field experiment carried out in 2008 at Experimental Sta-tion in Jadwisin Polish early potato cultivar Owacja was grown on sandy loam in 2 treatments embraced T0 (control) and T1 with water drip irrigation and nitro-gen (N) fertigation. Irrigation and N fertigation was conducted by Decision Sup-port System. Dry matter of leaves, stems and tubers was measured in the course of growing period at three different dates: 17, 28, 42 days after emergence (DAE). For these dates leaf area was estimated with use of leaf area meter LICOR 3100 and values of leaf area index (LAI) and specific leaf area (SLA) were calculated as well. Content of total nitrogen (Kjeldahl method by means of Kjeltec 2200 Foss Tecator ) in potato tubers was measured at 28, 42 DAE and at the death of foliage, 75 DAE. For these terms protein, dry matter yields and har-vest index were also calculated. Precise application of water and mineral nitrogen (T1) ensured very high yielding by early potato variety: almost 30 t•ha-1 at 42 DAE and 50 t•ha-1 at the end of growing period, that is at 75 DAE or 103 days after planting (DAP). Sup-plementary water and mineral nitrogen increased both final yields: dry matter by 4 t•ha-1 and protein by 230 kg•ha-1 in comparison with control, T0. It was shown the strong linear relationship between values of LAI for 42 DAE and final tuber yield. Both applied agents had positive influence on biomass distribution increas-ing harvest index by 0,05 compared to control, with its HI amounted to 0,78.
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