Soil Monitoring Methods to Assess Immediately Available Soil N for Fertigated Sweet Pepper

Excessive N application occurs in greenhouse vegetable production. Monitoring methods of immediately available soil N are required. [NO3−] in soil solution, sampled with ceramic cup samplers, and [NO3−] in the 1:2 soil to water (v/v) extract were evaluated. Five increasing [N], from very N deficient (N1) to very N excessive (N5) were applied throughout three fertigated pepper crops by combined fertigation/drip irrigation. The crops were grown in soil in a greenhouse. Soil solution [NO3−] was measured every 1–2 weeks, and extract [NO3−] every 4 weeks. Generally, for treatments N1 and N2, both soil solution and extract [NO3−] were continually close to zero, and increased with applied [N] for treatments N3–5. The relationships of both methods to the nitrogen nutrition index (NNI), an indicator of crop N status, were assessed. Segmented linear analysis gave R2 values of 0.68–0.70 for combined data from entire crops, for both methods. NNI was strongly related to increasing [NO3−] up to 3.1 and 0.9 mmol L−1 in soil solution and extracts, respectively. Thereafter, NNI was constant at 1.04–1.05, with increasing [NO3−]. Suggested sufficiency ranges were derived. Soil solution [NO3−] is effective to monitor immediately available soil N for sweet pepper crops in SE Spain. The extract method is promising.

Using simple RGB Camera to estimate Nitrogen Uptake, Nitrogen Nutrition Index (NNI) and critical Nitrogen: Spring wheat case study.

<p>The first Nc dilution curve was based on dry matter (DM) power function. This model is limited to  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.  </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 0–180 kg ha<sup>-1</sup>) and several  cultivars varying from shortest to longest ripening growth period. Nc reduced gradually from about 6% to 2%  ( =60-20 gr/Kg) when DM increased with DAE  from 0 to 14,000 kg/ha during 80 growing days.  NNI was stable and clearly distinct between   maximal index (1.0  and minimal index (0.2) when (DAE) was about 60;   Photographs succeeded to replicate laboratory measurements and obtained a linear regression curve with a unity  slop and r<sup>2</sup>=0.93. Nitrogen.  use efficiency (NUE) ranged from 50 to 65 kg  DM/unit N and from 30 to 50 Kg grain /unit N .</p>