Spring Wheat Response to Enhanced Ammonium Supply: II. Tillering

Spring wheat ( Triticum aestivum L.) grain dry matter (DM) is increased by increasing the proportion of fertilizer N as NH 4 in the presence of a nitrification inhibitor (enhanced ammonium supply, EAS). This yield increase is manifest in increased heads plant −1 . The objective of this study was to determine the effects of EAS on the number and origin of vegetative and headed tillers and on the number of fertile spikelets and kernels of each tiller. Knowledge of these effects will aid in determining when and how EAS increases grain DM. Increased grain DM with EAS in this study resulted from an increase in the number of headed tillers plant −1 , which, for the most part, resulted from an increase in the number of vegetative tillers plant −1 . Increases in vegetative tillers plant −1 were detectable within several days after the onset of tillering and were similar for a low‐tillering and a high‐tillering cultivar. The rate of mainstem development was not affected by EAS, but several tillers appeared earlier with EAS. For some tillers, EAS also increased the proportion of vegetative tillers forming heads. Increased grain DM was not proportional to increases in heads plant −1 , because the additional headed tillers produced with EAS treatments were primarily T0 (coleoptilar mainstem) tillers and subtillers that had fewer spikelets head −1 and kernels head −1 . The number of fertile spikelets head −1 of several tillers was increased by EAS treatments, but the number of kernels head −1 was increased for the T1 and T20 tillers, only. Negative effects of EAS treatments on late‐appearing tillers (T4, T5, and T22) were thought to result from increased self‐shading, increased plant wilting, and reduced soil‐N supply occurring at anthesis and resulting from the much greater plant DM prior to anthesis in EAS treatments. However, in general, increased spring wheat grain DM with EAS can be ascribed to the positive effects of EAS on tiller development.