Use and understanding of organic amendments in Australian agriculture: a review

Abstract

A wide range of organic amendments (OA) is currently available to Australian farmers. These products have numerous agronomic applications, including the supply of plant nutrients, control of pests and diseases, and in management of soil health. Several of these products are also used in contaminated and degraded land remediation. The most commonly identifiable groups of OA in Australia are composts, compost teas, vermicasts, humic substances, meat, blood and bone meal, fish hydrolysates, seaweed extracts, bio-inoculants, biodynamic products, and biochars. Many of these OA contain nutrients within organic molecular structures; these nutrients are usually not immediately available to plants and must first be mineralised. Mineralisation often occurs as OA are consumed by microbes, thereby stimulating soil microbial activity. The application of OA such as bio-inoculants, humic substances, and seaweed extracts can potentially stimulate crop growth and development through the actions of plant growth-promoting hormones, including cytokinins, auxins, and gibberellins. Yet despite these apparent benefits, the widespread adoption of OA in Australia has been limited, due in part to the high application rates required to produce agronomic benefits, a lack of consistency in the composition of some products, a poor public perception of their utility, and a lack of unbiased scientific research into the agricultural potential of these products.

Agricultural uses of plant biostimulants

“…Their modes of action are not yet well understood, but the application of new analytical and molecular tools is providing new insight into their effects on gene expression, biochemical pathways, and physiological processes Nair et al 2012;Jannin et al 2013;Wally et al 2013). Greater understanding of the modes of action of this renewable resource will be helpful in optimizing its use in the sustainable management of agricultural and horticultural systems (Khan et al 2009;Quilty and Cattle 2011).…”

Utilization of crops residues as compost and biochar for improving soil physical properties and upland rice productivity

“…It is widely known that organic amendments such as plant residues, manure or compost maturity should be used to improve soil quality. Compost contains significant amounts of valuable plant nutrients including N, P, K, Ca, Mg and S and a variety of essential trace elements (Smith a n d Collins, 2007;Quilty and Cattle, 2011;Fisher and Glaser, 2012). Thus, compost can be defined as an organic multi nutrient fertilizer (Smith and Collins, 2007;Amlinger et al, 2007).…”

Can Organic Amendments Support Sustainable Vegetable Production?

“…The wide-ranging benefits to agricultural soils that are reported worldwide from OA application studies are often associated with application rates that are many times larger than what is necessary to supplement N chemical fertilizer (Quilty and Cattle, 2011). The +CONV treatments included in this study that represent the OA standard farm practice, showed no improvement in crop biomass production when compared to the +Rd N fertilizer treatments.…”

“…This trend was already visible in the field study after 3 yr of the OA treatment. A common research finding is an increase of soil C following repeated application of OA, however, there is also evidence that reductions in soil C can occur due to increased C mineralization (Quilty and Cattle, 2011). For our study, the relatively small amount of Ma applied annually (average of 2.08 t ha -1 ), combined with an average C/N ratio of 3.3 could have promoted a priming effect on the native soil C. Differences between Co and Ma could, however, be attributed to the net amount of C applied and its stability (resistance against degradation), which the amount of C applied was on average six times higher in the Co treatment than Ma.…”