SOIL-WATER EFFECTS ON GROWTH AND NUTRITION IN UPLAND PASTURES

Normally the oceanic climate of Scotland maintains soils at low levels of soil water deficit. Field data for such a year are presented and c ompared with those for an unusually dry year, with the objective of as sessing to what degree dry spells might limit herbage production in up land pastures, One meter square plots were sampled on selected dates o n reseeded pastures growing on each of 3 cambisols, each derived from different parent materials, The swards were unfertilized and maintaine d at nominal heights of 2, 4, 7, and 10 cm by cutting every 2 or 3 wee ks to manipulate growth and demand for P and N. Overall yield was 25 t o 50% lower in the dry year compared with an average year. Peaks and t roughs in growth rates, measured as yield at each cutting, and in P an d N content, corresponded to changes in soil water deficit in the top meter of soil, The linear correlation coefficient between soil water d eficit and growth rate was -0.894 (P = 0.001), Although there was some variation in volumetric water content between soils, soil water defic its were similar in all the cambisols, Yields and nutrient contents we re generally similar for herbage harvested from the 2 soils having bas ic parent material (one a eutric and one a dystric cambisol) and lower on the dystric cambisol derived from schists, The effects of water co ntent largely over-rode cutting treatments, demonstrating that dry spe lls occasionally occuring in the oceanic climate of Scotland can signi ficantly affect grassland production.