Soil water effects on growth and nutrition in upland pastures.

Abstract

Normally the oceanic climate of Scotland maintains soils at low levels of soil water deficit. Field data for such a year are presented and compared with those for an unusually dry year, with the objective of assessing to what degree dry spells might limit herbage production in upland pastures. One meter square plots were sampled on selected dates on reseeded pastures growing on each of 3 cambisols, each derived from different parent materials. The swards were unfertilized and maintained at nominal heights of 2, 4, 7, and 10 cm by cutting every 2 or 3 weeks to manipulate growth and demand for P and N. Overall yield was 25 to 50% lower in the dry year compared with an average year. Peaks and troughs in growth rates, measured as yield at each cutting, and in P and N content, corresponded to changes in soil water deficit in the top meter of soil. The linear correlation coefficient between soil water deficit and growth rate was -0.894 (P = 0.001). Although there was some variation in volumetric water content between soils, soil water deficits were similar in all the cambisols. Yields and nutrient contents were generally similar for herbage harvested from the 2 soils having basic parent material (one a eutric and one a dystric cambisol) and lower on the dystric cambisol derived from schists. The effects of water content largely over-rode cutting treatments, demonstrating that dry spells occasionally occurring in the oceanic climate of Scotland can significantly affect grassland production.