COMPARISON OF THE EFFECT OF NO3- AND NH4-N ONGROWTH, YIELD, AND YIELD COMPONENTS OF MANITOU SPRING WHEAT AND CONQUEST BARLEY

Abstract

The objective of this study was to compare the effects of NO3 and NH4 forms of nitrogen on the growth and yield of spring wheat and barley. Two growth-room experiments were carried out using spring wheat (Triticum aestivum L. ’Manitou’) in both experiments and barley (Hordeum vulgare L. ’Conquest’) in the second. NO3 or NH4-N plus the nitrification inhibitor nitrapyrin were applied at rates from 23 to 360 kg N/ha. Temperatures were 27/12 °C (day/night) and soil moisture was maintained at between −0.05 and −1.0 bars by frequent watering. NO3-N-treated plants were taller, and had thicker stems and more spikelets/spike than NH4-N-treated plants. The NH4-N-treated plants produced more spikes and matured faster initially, although by anthesis stage there was little difference in maturity between the NO3- and NH4-N-treated plants. There was no differential effect of nitrogen source on total dry matter at maturity, although dry matter increased in proportion to nitrogen rate. Grain yield of the NH4-N-fed plants was higher than that of the NO3-N-fed plants, especially at the higher nitrogen rates. This was due primarily to the effect on number of spikes produced and secondarily on seed set. It is suspected that denitrification losses of nitrogen from the NO3-N-treated soil contributed to the differential response to the two sources, but there was circumstantial evidence to suggest that some of the difference may have been due to the inherent nature of the two sources which might have affected their ease of metabolism by the plant.