Best bet management of ameliorated non-wetting soils for the Geraldton Port Zone (GPZ)

Commencement date: July 2016

Completion date: July 2018

Funding: GRDC-RCSN project

Location: Marchagee, Eneabba, Irwin

Collaborators: DAFWA, CSBP, Liebe Group, Mingenew Irwin Group (MIG)

Project Aim: This project aims to investigating the best way to apply nutrients on a cultivated non-wetting soil.

Background:

Water Repellence is a significant constraint to production in Western Australian broadacre farming systems. It is estimated that 6.9 million hectares are considered at moderate risk of water repellence, whilst 3.3 million hectares are considered at high risk, based on the area of coarse sands with low clay content (van Gool 2008). In the Geraldton Port Zone, approximately 52% of the arable soils are at moderate to high risk of water repellence, with the Shires of Irwin (87%), Coorow (67%), Northampton (66%), Three Springs (62%), Carnamah (53%), and Perenjori (50%) all having over 50% of their soils at medium-high risk.

Water repellent soils are defined by having slow permeability to water, characterised by uneven wetting at the surface, water run-off and ponding and/or flow through the soil via preferential pathways leaving surrounding soil dry (Roper et al. 2015). The consequential impact on the crop is uneven germination, poor crop establishment, reduced nutrient use efficiency and reduced yields. The opportunity cost of the constraint is an estimated $250 m for WA agricultural production, $68.8 m for the northern agricultural region (Herbert 2009).

This project will be looking closely at the impact of soil cultivation practices, which have been adopted to mitigate water repellency, on the interactions of potassium and nitrogen within the soil profile. Sites were selected based on prior farmer knowledge that non-wetting was an issue at the site and, have used a cultivation practice to mitigate this. The sites selected have either been mouldboard ploughed or spaded, approximately 2-4 years prior to establishment of this trial. The purpose of this cultivation time gap is to investigate the effects of a settling cultivated soil on nutrient availability. It is understood that cultivation practices can release an uneven ‘burst’ of nutrients throughout the soil profile, leading to potential nutrient deficiencies or toxicities in the first season after cultivation. While this is widely understood, yet difficult to measure, it is the settling period greater than one season out of cultivation, which requires further research and development.

The outcomes of this trial will provide new rules of thumb on nutrition rates and application methods, on a range of soil types, influenced by cultivation practice.

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