You can manage bookmarks using lists, please log in to your user account for this.
Media type:
E-Article
Title:
Nitrogen Requirements and N Status Determination of Lettuce
Contributor:
Bottoms, Thomas G.;
Smith, Richard F.;
Cahn, Michael D.;
Hartz, Timothy K.
imprint:
American Society for Horticultural Science, 2012
Published in:HortScience
Language:
Not determined
DOI:
10.21273/hortsci.47.12.1768
ISSN:
0018-5345;
2327-9834
Origination:
Footnote:
Description:
<jats:p>As concern over NO<jats:sub>3</jats:sub>-N pollution of groundwater increases, California lettuce growers are under pressure to improve nitrogen (N) fertilizer efficiency. Crop growth, N uptake, and the value of soil and plant N diagnostic measures were evaluated in 24 iceberg and romaine lettuce (<jats:italic>Lactuca sativa</jats:italic> L. var. <jats:italic>capitata</jats:italic> L., and <jats:italic>longifolia</jats:italic> Lam., respectively) field trials from 2007 to 2010. The reliability of presidedressing soil nitrate testing (PSNT) to identify fields in which N application could be reduced or eliminated was evaluated in 16 non-replicated strip trials and five replicated trials on commercial farms. All commercial field sites had greater than 20 mg·kg<jats:sup>−1</jats:sup> residual soil NO<jats:sub>3</jats:sub>-N at the time of the first in-season N application. In the strip trials, plots in which the cooperating growers’ initial sidedress N application was eliminated or reduced were compared with the growers’ standard N fertilization program. In the replicated trials, the growers’ N regime was compared with treatments in which one or more N fertigation through drip irrigation was eliminated. Additionally, seasonal N rates from 11 to 336 kg·ha<jats:sup>−1</jats:sup> were compared in three replicated drip-irrigated research farm trials. Seasonal N application in the strip trials was reduced by an average of 77 kg·ha<jats:sup>−1</jats:sup> (73 kg·ha<jats:sup>−1</jats:sup> vs. 150 kg·ha<jats:sup>−1</jats:sup> for the grower N regime) with no reduction in fresh biomass produced and only a slight reduction in crop N uptake (151 kg·ha<jats:sup>−1</jats:sup> vs. 156 kg·ha<jats:sup>−1</jats:sup> for the grower N regime). Similarly, an average seasonal N rate reduction of 88 kg·ha<jats:sup>−1</jats:sup> (96 kg·ha<jats:sup>−1</jats:sup> vs. 184 kg·ha<jats:sup>−1</jats:sup>) was achieved in the replicated commercial trials with no biomass reduction. Seasonal N rates between 111 and 192 kg·ha<jats:sup>−1</jats:sup> maximized fresh biomass in the research farm trials, which were conducted in fields with lower residual soil NO<jats:sub>3</jats:sub>-N than the commercial trials. Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha<jats:sup>−1</jats:sup>·d<jats:sup>−1</jats:sup>. N uptake then increased linearly until harvest (≈9 weeks after planting), averaging ≈4 kg·ha<jats:sup>−1</jats:sup>·d<jats:sup>−1</jats:sup> over that period. Whole plant critical N concentration (N<jats:sub>c</jats:sub>, the minimum whole plant N concentration required to maximize growth) was estimated by the equation N<jats:sub>c</jats:sub> (g·kg<jats:sup>−1</jats:sup>) = 42 − 2.8 dry mass (DM, Mg·ha<jats:sup>−1</jats:sup>); on that basis, critical N uptake (crop N uptake required to maintain whole plant N above N<jats:sub>c</jats:sub>) in the commercial fields averaged 116 kg·ha<jats:sup>−1</jats:sup> compared with the mean uptake of 145 kg·ha<jats:sup>−1</jats:sup> with the grower N regime. Soil NO<jats:sub>3</jats:sub>-N greater than 20 mg·kg<jats:sup>−1</jats:sup> was a reliable indicator that N application could be reduced or delayed. Neither leaf N nor midrib NO<jats:sub>3</jats:sub>-N was correlated with concurrently measured soil NO<jats:sub>3</jats:sub>-N and therefore of limited value in directing in-season N fertilization.</jats:p>