<p>The first Nc dilution curve was based on dry matter (DM) power function. This model is limited to&#160; point of singularity near zero. Another disadvantage was that it required meaasurements of DM which is time and labor consuming. Alternatively we proposed a logistic model that starts at zero and on the abscissa assumed a linear relationship between days after emergence (DAE) and DM throughout the relevant stages of wheat growth cycle. &#160;</p><p>The Objectives of this study were to: 1) To demonstrate the feasibility of digital camera to replace laboratory tests. 2) To Determine critical N (Nc) and Nitrogen nutrition Index(NNI) of spring wheat and 3) Use N% and dry matter yield in order to calculate N uptake by wheat. This last is expected to be a tool to calculate the required amount of nitrogen to obtain maximum yield.</p><p>Wheat experiments were conducted in greenhouse lysimeters. Varied rates of N fertilizer (equivalent to 0&#8211;180 kg ha<sup>-1</sup>) and several&#160; cultivars varying from shortest to longest ripening growth period. Nc reduced gradually from about 6% to 2%&#160; ( =60-20 gr/Kg) when DM increased with DAE&#160; from 0 to 14,000 kg/ha during 80 growing days.&#160; NNI was stable and clearly distinct between &#160;&#160;maximal index (1.0 &#160;and minimal index (0.2) when (DAE) was about 60;&#160;&#160; Photographs succeeded to replicate laboratory measurements and obtained a linear regression curve with a unity&#160; slop and r<sup>2</sup>=0.93. Nitrogen.&#160; use efficiency (NUE) ranged from 50 to 65 kg&#160; DM/unit N and from 30 to 50 Kg grain /unit N&#160;.</p>
Simple Assessment of Nitrogen Nutrition Index in Summer Maize by Using Chlorophyll Meter Readings
