The influence of phosphate fertilizer on the growth and yield of wheat in soil infested with cereal cyst nematode (Heterodera avenae Woll.)

Abstract

In a field experiment, the numbers of immature females of cereal cyst nematode (Heterodera avenae Woll.) on roots of wheat at anthesis were 14 1, 220 and 324 per plant with 0, 100 and 400 kg/ha superphosphate respectively. The field site, with an average annual rainfall of 450 mm, was located at Coonalpyn, S.A. (35¦4 1'S., 139¦ 52'E.) on a grey-brown, calcareous, loamy earth. Wheat seedlings were grown under controlled environment conditions in two soils with identical chemical and physical properties, but with initial populations of H. avenae of 1.1 and 5.8 eggs/g soil to study the response in shoot and root growth to superphosphate either mixed through the soil or banded with the seed. Using aldicarb, it was shown that H. avenae reduced the length of seminal root axes per plant by 33% in soil containing 1.1 eggs of H. avenae/g and by 74% in soil containing 5.8 eggs/g. Length of seminal root axes was not affected by superphosphate. The length of lateral roots per plant was increased by controlling H. avenae with aldicarb in soil containing 5.8 eggs/g but not in soil containing 1.1 eggs/g. When superphosphate was banded with the seed, the length of lateral roots per plant increased by 33% in soil containing 1.1 eggs/g and by 55% in soil containing 5.8 eggs/g. In soil containing the lower initial population of H. avenae, shoot dry weight was increased by 97% when superphosphate was mixed through the soil and 100% when banded with the seed. However, in soil containing the higher initial population of H. avenae, the responses were 48 and 94% to mixed and banded superphosphate respectively, indicating that plants severely infected with H. avenae are less able to utilize phosphate distributed through the soil. The results have practical implications in that the method of application and amount of superphosphate in fields infested with H. avenae will affect the build-up of the nematode when cereals are grown; furthermore, in infested soils, the plant response to superphosphate would be greater when the fertilizer is banded with the seed.