Response of soil fertility indices to a short phase of Australian woody species, continuous annual crop rotations or a permanent pasture

Roots modify the environment in which they grow and can be tactically used to condition the soil for the benefit of following generations of plants. In this study, we evaluated changes in selected nutritional and biological properties of the soil after growing a range of plant types as treatments that modified soil structure through creation of biopores. The plant types were: (i) 6 years of a mixture of Australian native woody species grown in belts followed by 1 year of cereal crop (belt-soil); (ii) rotation of annual crops (cropping-soil); (iii) a permanent pasture (pasture-soil). Although the number of biopores found in the A-horizon was similar for the belt-soil and cropping-soil, the former had larger air-filled porosity. Differences in fertility indices of the A-horizon amongst the treatments were, however, not associated with those in structure, but were linked to conservation of organic matter. The short phase of woody perennials restored both total C and total N in the top 0.1 m of the soil profile to 93% that found under a 25-years-old permanent pasture, without the fall in pH found in the latter. Increases in total C were primarily associated with high input of organic matter in the belt-soil where the organic matter was also protected from possible losses by oxidation and physical removal due to absence of tillage for 6 years. There was no evidence that the woody species enhanced cation cycling between the topsoil and subsoil, because exchangeable Ca was similar in the A-horizon of the belt-soil and cropping-soil, although this cation was lower in the B-horizon of the belt-soil. The 6 years phase of native woody species reduced inoculum level of root pathogen Rhizoctonia solani Kuhn. Compared to the bulk soil, the area bordering the biopores (biopore-sheath) in the belt-soil was richer in nutrients (total C and total N) and so supported a larger microbial population, which was dominated by cellulolytic fungi. This study showed the potential for short phases of woody perennials in soil management and the attraction for their incorporation in designing new cropping systems for sustainability.