Heritabilities of Quantitative Attributes of Oats ( Avena sp.) at Varying Levels of Environmental Stress 1

We grew 27 oat cultivars at 3 levels of soil nitrogen, 4 levels of soil phosphorus, and 3 planting dates to examine the reactions of several agronomic characters to degrees of environmental stress. Each environmental factor was varied in a separate experiment. The experiments were grown in split‐plot designs in which wholeplots were levels of the environmental variables and subplots the cultivars planted in hills spaced 1 foot apart in perpendicular directions. The degree of stress imposed by a certain level of environmental factor was measured by the relative productivity of the attribute in question. For most attributes, stress was reduced with increasing increments of nitrogen and phosphorus and with earlier plantings. However, adding nitrogen increments increased the stress for 100‐seed weights, and early planting increased stress for number of spikelets per panicles and 100‐seed weights. Intraplant competitive, caused by the increased numbers of panicles produced per plot when nitrogen was applied or the oats were planted earlier, may have induced stress on spikelet and seed development. In general, genotypic variances among the oat cultivars increased as the environmental stresses were reduced. Environmental variance, however, also tended to increase so that heritabilities did not always increase with reduced environmental stress.