Field Guide. cropping and pastoral grazing on flat to rolling country.

PLANT INDICATORSSurface ponding under pasture Assess the degree of surface ponding.Base your assessment on ponding present at the time, or your generalrecollection of the time ponded water took to disappear after a wetperiod, or after heavy rainfall in the winter (see opposite). Yellow orpale patches of pasture, or pasture lying flat over the surface indicaterecent surface ponding.THE LENGTH OF TIME WATER REMAINS PONDED on the surfaceindicates the rate of infiltration into the soil, <strong>and</strong> the time the soil remainssaturated. Prolonged waterlogging depletes oxygen <strong>and</strong> causes carbondioxide to build up. Anaerobic conditions develop, <strong>and</strong> chemical <strong>and</strong>biochemical reactions produce by-products toxic to plant roots. PlantavailableN is lost through denitrification, pastures become pale oryellow, <strong>and</strong> photosynthesis declines. Root damage reduces nutrient <strong>and</strong>water uptake <strong>and</strong> plants can wilt <strong>and</strong> lie on the surface. Prolongedsurface ponding makes soil more susceptible to pugging, <strong>and</strong> pastureplants to treading damage. It decreases pasture growth <strong>and</strong> utilisation,<strong>and</strong> can alter pasture species composition.80 VISUAL SOIL ASSESSMENT: Volume 1