Interception of light by model hedgerow orchards in relation to latitude, time of year and hedgerow configuration and orientation.
Light interception by model hedgerow orchards and light distribution over their surfaces were investigated using a computer for the direct light calculations and a graphical technique to study the distribution of diffuse light under both uniformly luminous and standard overcast skies. Model hedgerows of triangular, truncated triangular and rectangular section, each with 3 different ratios of hedgerow height to alley width were considered at latitudes 51.3, 45 and 34 deg N. When only half the ground area was covered with hedgerow and the hedgerow height was equal to the alley width over 80% of available light could be intercepted. As the ratio of hedgerow height to alley width was increased the direct light interception increased in much smaller proportion. Light interception was reduced with decreasing angle of the hedgerow sides to the horizontal and at lower latitudes, especially for E-W oriented hedgerows. Although there was little change in percentage interception by N-S orbited hedgerows as the season progressed, there was a marked seasonal pattern of interception by E-W hedgerows and this varied with latitude. As hedgerow height was increased so was the proportion of poorly illuminated surface, and as the angle to the horizontal was decreased the evenness of illumination over a hedgerow side was increased. The illumination of the S faces of E-W hedges was relatively evenly distributed, the uniformity being greater for short than for tall hedgerows, sloping than vertical sides and at low latitudes than at high latitudes, but it varied considerably with time of the year for some hedgerow configurations. The interception and distribution of diffuse light was rather similar to that of direct light for N-S hedgerows. The effects of latitude on light interception by and distribution over hedgerow systems of differing proportions appeared large enough to influence significantly the value of different systems of planting. This will apply to other row crops as well as hedgerow orchards.