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

PLANT INDICATORSCrop emergence Assess the degree <strong>and</strong> uniformity of crop emergence within a monthof sowing by comparing the number <strong>and</strong> height of established plantswith the three photographs provided.GOOD SEED GERMINATION AND PLANT EMERGENCE depend onfactors that include the quality of soil tilth at the time of sowing <strong>and</strong>during the weeks immediately following. Soils that have poor structurethrough compaction <strong>and</strong> over-cultivation can resettle <strong>and</strong> consolidaterapidly after the seed bed has been prepared. Impeded water <strong>and</strong> airmovement through the soil can give rise to small areas low in oxygen(anoxic zones). These produce chemical <strong>and</strong> biochemical reductionreactions, the by-products of which are toxic to plants. These anoxiczones <strong>and</strong> poor soil aeration reduce seed germination <strong>and</strong> plantemergence. As a result, bare patches <strong>and</strong> poor <strong>and</strong> uneven early growthare commonly observed throughout paddocks that have poor soilstructure. Young plants can also show off-colouring of leaves <strong>and</strong>moisture stress.The loss of soil structure can reduce crop establishment of barley from315 to 131 plants/m 2 , <strong>and</strong> grain yields from 6.7 to 3.9 t/ha. Corngermination slows, <strong>and</strong> plant populations also decrease. Seedlingmortality of winter cereals can be high if the soil is waterlogged formore than 3 to 4 days between germination <strong>and</strong> emergence.34 VISUAL SOIL ASSESSMENT: Volume 1