Nearly all cropping soils in Australia are susceptible to problems of high soil strength. It is widely accepted that high soil strength leads to a reduction in crop rooting depth and access to nutrients and water, but it can also reduce early branching of shoots, independent of water and nutrient supply. Current understanding about effect of high soil strength on different crop species is poor, with no published guidelines and just a one size fits all approach.
This paper reports on the response of 4 field crops in 2024 to a sandy soil of high strength at Avon, in South Australia. The four crops were wheat, canola, lentils and tillage radish. Each were grown on unamended or deep ripped (to relieve high soil strength) plots with 4 replicates. Wheat was also grown with two N regimes to investigate the impact of high soil strength on early branching.
Deep ripping reduced soil strength in the top 40 cm of the soil profile from penetrometer resistances well above 3,000 kPa to less than 1,500 kPa. Growth of lentils and tillage radish were most affected by high soil strength (measured as the reduction in growth from ripped to unamended situations) followed by canola and low-N wheat. Wheat with a high N regime was least affected by high soil strength.
High soil strength reduced early branching in wheat and lentils but there was little evidence that it decreased the depth or extent of root systems at maturity of any crops. Soils after harvest under all 3 grain crops were almost as dry in unamended soils as they were after ripping. Wheat was generally more tolerant of high soil strength than broad-leafed crops. The trial will be seeded to wheat in 2025 to investigate legacy effects from treatments imposed in 2024.