Establishment of Continuous Critical Levels for Indices of Plant and Presidedress Soil Nitrogen Status in the Potato Crop

Abstract

Critical levels for six plant and pre-sidedress soil nitrogen indices were established for the growing season and their relative accuracy to diagnose the need for supplemental sidedress N was also compared. Field trials were conducted from 1996 to 1998 with irrigated potato in North-eastern Portugal. Fertilizer treatments included several pre-plant and sidedress N rates. Petiole nitrate concentrations (determined by a standard laboratory method and with the portable RQflex reflectometer), leaf N content, leaf greenness (SPAD-502 chlorophyll meter), pre-sidedress soil NO 3 -N and pre-sidedress soil inorganic-N (NO 3 -N + NH 4 -N) were selected as N indicators. The Cate-Nelson graphical method and an analytical procedure using Mitscherlich type curves were used to determine critical levels. In both cases, a yield reduction of 10 % was accepted. The accuracy of the diagnostics was estimated from the Cate-Nelson graphical method, quantifying the point percentage that appears in negative quadrants (the error rate). The graphical method yielded lower critical levels, appearing as the The N indicators with lower error rate were the pre-sidedress soil NO 3 -N and pre-sidedress soil inorganic-N (both showing an error rate of 8.3 %), followed by petiole nitrate concentration (determined in laboratory, 12.0 %, and with RQflex reflectometer,12.5 %), leaf N content (13.0 %) and leaf greenness (14.6 %). Error rates were similar throughout the growing season, meaning that is possible to get information about the need for supplementary N in the very early growth stages.

Soil‐ and Plant‐Based Indices in Potato Production in Response to Polymer‐Coated Urea

“…6f). This observation was also reported in other studies for potato (Bélanger et al, 2001b; Rodrigues, 2004; Wilson et al, 2009). However, unlike Bélanger et al (2001b), our critical value was considerably increased when soil NH 4 –N was included in the model (85–132 kg N ha −1 ).…”

Potato Response to a Polymer‐Coated Urea on an Irrigated, Coarse‐Textured Soil

“…Belanger et al (2001) and Rodrigues (2004) also found that soil NO 3 –N was the best method for potato, and that the inclusion of NH 4 –N did not improve the test. Meisinger et al (1992), however, found that the addition of soil NH 4 –N was advantageous to determining the CV for corn yields and suggested that it more accurately represented the total availability of N to the crop.…”

“…Petiole NO 3 –N concentration is a widely accepted method to determine potato plant N status during the growing season (Porter and Sisson, 1991; Belanger et al, 2003; Rodrigues, 2004). Rosen and Eliason (2005) have listed optimal ranges for petiole NO 3 –N concentrations in the Upper Midwest depending on the growth stage of the potato plant and are highlighted in gray in Fig.…”

“…3). The critical value (CV) is defined as the point on a curve that relates the soil N to the yield; below or above this point there is a high probability that the crop responds (below) or not (above) to supplementary applications of N (Rodrigues, 2004). This point on a quadratic plateau model is where the quadratic line intersects the linear line.…”

A Review of Methods to Improve Nitrogen Use Efficiency in Agriculture

“…This indicates that estimation of yield and potential for N response in relative terms is possible. Several studies were conducted to improve the relationship between crop yield and sensor readings [65,106,107,[131][132][133], however, their practical application is still in question due to their inconsistent results.…”