Growth and Root Morphology of Corn as Influenced by Nitrogen Form

Abstract

Public concern about NO‐3 levels in potable waters, together with improving techniques for maintaining NH4+ availability in soils, has renewed research interest in the effects of N form on crop growth. The effects of NO‐3 versus NH+4 on growth and morphology of juvenile corn (Zea mays L.) were investigated in two experiments. In Exp. 1, 16‐d‐old, solution‐grown plants produced less shoot fresh weight when grown with NH+4 than with NO‐3 nutrition. Root fresh weights were similar, but elongation of the primary root axis and its longest first order lateral was less with NH+4 nutrition. Under NH+4 nutrition, apparent thickness (grams per meter) of primary roots was 54% greater, and the frequency of first order laterals with second order laterals was 65% greater, than under NO‐3 nutrition. In Exp. 2, plants were grown in the greenhouse until 40 d after emergence in a slightly alkaline 3:1 sand:soil mix. Nitrogen (75 mg N kg−1) was supplied as either Ca(NO3)2 or (NH4)2SO4 plus nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine]. Ammonium‐grown plants produced 2.3 times the dry matter and had higher concentrations of N in both stems (18.5%) and leaves (27.5%) compared to NO‐3‐ grown plants. Tillering was increased by NH+4‐ nutrition. Apparent root thickness was again greater under NH+4 nutrition, but the difference between N regimes was only 15%. Results indicate that under conditions of course‐textured soils and slightly alkaline pH an enhanced NH+4‐ N regime may be advantageous for growth of corn. Differences in pH regimes between the hydroponic and soil‐based experiments may account for the contrasting results.

Nitrogen form effects on early corn root morphological and anatomical development

“…Stelar area tended to be greater under N03-N and cortical area tended to be greater under NH4-N. As a result of these trends, the percent of total area occupied by cortex was significantly greater under NH4-N (Table 4). DISCUSSION Superior growth in a strict NH4-compared to a strict NO3-N regime observed in this experiment (Table 1) contrasts with other controlled environment corn growth studies (4,8,13). We believe our results are due to maintaining pH with MES buffer in a range where NH4 is the preferred N form (12,21).…”

“…Since roots are not able to penetrate soil pores of smaller diameter (15), root thickening may be particularly detrimental in compacted or fine textured soils. Shorter roots due to NH4-N nutrition has also been reported (8,11,13,16). This Downloaded by [Cornell University Library] at 21:49 17 November 2014 effect of NH4-N can limit the soil volume exploited by roots.…”

“…Calculated root thickness (g/m root) for the primary root system of corn grown in weakly buffered hydroponic culture was 54% greater under NH4-N compared to NO3-N nutrition (13). Under conditions favoring the enhanced NH4 regime (coarse textured, slightly alkaline soil) a similar tendency towards thicker roots with NH4-N was seen for the entire root system of 38 d plants, although the difference between N-regimes was only 15% (13).…”

“…Increasing the pH from 5 to 7 with CaCO3 in sand culture improved corn growth under enhanced NH4 supply (12). In a pot experiment using a light textured, slightly alkaline soil Teyker and Hobbs (13) found that an enhanced NH4 regime (NH4SO4 plus Nitrapyrin) produced 2.3 times as much dry matter and higher shoot N concentrations compared to Ca(NO3)2-N. Dibb and Welch (14) showed that adequate potassium fertilization was important to maximizing growth under enhanced NH4 supply.…”

The Influence of Nitrogen Nutrition on the Carbohydrate and Nitrogen Status of Emergent Macrophyte Acorus calamus L.

“…A correlation between NH þ 4 -N nutrition and a high tissue N content was also detected in non-wetland species (e.g. wheat Lewis, 1993a andmaize Teyker &Hobbs, 1992;Cramer & Lewis, 1993a). Although an increase in both total C and N was found in the tissues of Acorus plants under both high N and pure NH þ 4 -N nutrition, more dramatic changes in tissue N rather than tissue C content resulted in a significant shift in tissue C/N balance towards N metabolism, like in Carex rostrata (Saarinen, 1998).…”