Effect of the Weather on Hay Production

Although the average maximum soil moisture deficit (SMD) at Cockle Park is small (80 mm) its variation from year to year has a major impact on hay production. There is a significant negative correlation between maximum SMD and hay yield but the relation is strongest on the lower yielding plots, possibly because these have the poorest root growth and soil conditions (Table 1). The plots can be separated into two groups (the higher yielding(1-5) and the lower yielding(6, 7, 9 and 11)) which have yields which inter-correlate well with others within the group but not with those in the other group (Table 2). This indicates that good soil conditions and manuring mitigate the adverse impacts of extreme weather, including increased droughtiness, and have a clear relevance if the regional climate is to be come drier in summer in the future. Counter-intuitively the lower yielding plots are more adversely affected by dry conditions. For more details see Coleman, Shiel and Evans (1987). In recent years the rainfall distribution has been advantageous for hay production, with relatively wet conditions occurring in May - the individual month whose water deficit is best related to hay yield.

Table 1. Yield of hay and the correlation between it and the Maximum SMD for each plot over the years 1898-1980

Table 2. Correlation coefficients between hay yields (1898-1980) for plots placed in decreasing order of yield. All are significant at P<0.001.