Pasture growth and soil fertility

Spring‐sown maize, marrow‐stem kale. and potatoes, followed by autumn‐sown Italian ryegrass. were grown for four years on land previously under good pasture for 14 years. High crop yields were maintained over the four years if fertilisers were applied. Inadequate nitrogen limited production of maize and potatoes after the first year. and inadequate nitrogen and po~sibly sulphur limited the production of kale after the first year. There was no evidence that cropping produced physical deterioration of the soil sufficient to affect growth of any of the crops. Soil organic matter was decreasing at the rapid annual rate of about 5 per cent when the soil was kept fallow but to a smaller extent when plants were grown. Discrepancies between the amounts of nitrogen mineralised and used by the crops and ryegra~s suggest that losses of available nitrogen occurred. Exchangeable cations decreased significantly and the use of urea was accompanied by a considerable drop in exchangeable calcium. base saturation. and pH.