GROWTH OF FIELD PEA ON RED-BROWN EARTH SOILS IN A YEAR WITH HIGH RAINFALL

A study of 4 commercial crops of peas was conducted in the Lower North of South Australia during 1992 to assess the importance of waterloggi ng on growth and yield. The area chosen for the survey has a high prop ortion of red-brown earth soils that slake and seal, have poor interna l drainage, and are prone to transient waterlogging. Rainfall in the y ear of the survey was above average, particularly during September and October, and waterlogging and disease were common in pea crops throug hout the region. Based on air-filled porosity and soil water tension, waterlogging occurred in each of the survey paddocks. Differences in v egetative growth and grain yields within and between paddocks could be related to the severity of waterlogging. There were differences betwe en the 4 survey paddocks for concentrations of potassium, sodium, iron , and manganese in pea shoots, and these differences appeared to corre spond to differences in the severity of waterlogging. Nutrient concent rations were, however, confounded by differences in soil pH and soil f ertility. Despite adequate to high levels of available phosphorus (P) in each of the 4 paddocks, concentrations of P in shoots were generall y low and, in 2 cases, indicated P deficiency. Phosphorus concentratio ns were not related to the concentration in the soil or to the severit y of waterlogging. In field experiments conducted over 2 seasons (1991 , 1992), peas were grown in raised hill plots to promote drainage arou nd the upper root system. The method significantly increased plant est ablishment in both years, and in 1992, a year of record high rainfall, grain yields from the drained plots were 5-64 times greater than thos e from undrained plots. In 1991, a year with lower rainfall, drainage improved pod yield by 13%. Observations during the survey suggested th at disease was worse in the paddocks that were severely affected by ex cess water.