Ageing of pastures is likely to affect the degree of potential water repellency in the long term, whereas seasonal variation on a shorter term affects the actual repellency of soils. A 1-year study on two pastures of different ages was conducted on a sandy soil to assess changes in the degree of potential and actual water repellency in relation to different levels of applied nitrogen (N). Sampling was carried out on four dates (April, June, August and October) to determine soil moisture content and both potential and actual water repellency at three depths (0¿25, 25¿50 and 50¿75 cm). The relative number of potentially wettable samples for the young pasture (5 years) ranged from 64% (0¿25 cm) to 96% (25¿50 cm) to 100% (50¿75 cm). For the old pasture (38 years) this ranged from 29 to 66 to 94%. The transition zone in which topsoil samples could be either wettable or water repellent ranged from 18 to 23% (v/v) for the young pasture compared with a range from 29 to 32% (v/v) for the old pasture. Thus, ageing pastures may result in both moving as well as decreasing transition zones over time. A positive relationship between increased inputs of fertilizer N, higher DM yields, lower soil water contents and higher degrees of water repellency was found for the old pasture for the August series. This suggests that seasonal variation in water repellency can be further re-enforced through nutrient management.
- sandy soil
- preferential flow