The energy balance approximation of Penman, used to estimate potential evapotranspiration, was tested for daily estimates on 37 days during 1956 and 1957. Though the Penman estimates were highly correlated with those obtained from detailed energy balance measurements, the absolute values of the Penman estimates were much too small. In order to obtain suitable daily estimates of evapotranspiration with the Penman method, a wind function that accounts for surface roughness and direct measurements of radiation energy were found necessary. The stomatal and daylength factors proposed by Penman and Schofield appeared to have little basis for general application.

Synopsis Measurements of potential evapotranspiration indicate that mean temperature cannot be relied upon for general use in estimating evapotranspiration during short‐periods. Mean temperature methods can be used with limited success for long‐period (growing season and annual) estimates of potential evapotranspiration, but energy balance methods are preferable if radiation data are available.

Spring wheat seeding rates of 22, 45 , 6.7 , and 101 kg/ha were compared in a field expenment otr a -"diu--textured soil at Swift CJirent, Saskatchewan, over the peiiod tloo-te68. Data

The plots were harvested with a combine and the yield/ha was calculated; 1,000-seed weights were obtained and samples were analyzed for oil content.

Yields within the sheltered area ransed from 2-l'to 437" abole check yields' Maximum grain production was obtiined in the area of maximum 'uvind and evaporation-reduction. Hou.ever, yields in general were extremely variable throughout the test area during individual yea'rs, and from year to 1'ear. The wide i-ariatior-rs in yield suggesithat the effects of u'indbreaks on other en\:ronmental factors should be considered in srudies of this nature.