Response of Potassium Uptake via Co-Placement with Phosphorus and Soil Amelioration with Gypsum

Abstract

<p>To investigate the impact of co-placement of K fertiliser with P fertiliser, a paddock trial and glasshouse trial were conducted using soil from two sites with sodic subsoil constraints. It was hypothesised that as plant roots proliferate around P bands in soil, placing K fertiliser in these bands would increase K uptake. In soils with sodic subsoil constraints root proliferation may be compromised. We therefore created a second hypothesis that addressing these constraints with gypsum would further increase K recovery when co-located with P.</p> <p>However, the addition of gypsum may inadvertently reduce the availability of P in bands due to precipitation of calcium phosphate in alkaline soils. Fertilisers used were mono-ammonium phosphate (MAP), potassium chloride (KCl) and calcium sulfate (gypsum). Wheat was grown as the test species. Both sites were near Croppa Creek in Northern New South Wales (NNSW). The paddock trial was run in site I, and the glasshouse trial used soil from site I and site II. Site I responded more to the treatments than site II.</p> <p>Arbuscular mycorrhizal fungi (AMF) responses were measured in the glasshouse trial along with plant growth parameters such as root growth, tiller count and shoot weight. There was no significant response of P or K on AMF colonisation. There was a decrease in AMF colonisation in relation to gypsum application in site I, however, it was not significant. Site II had a significant positive response to gypsum application. There was no correlation between AMF and root growth found. Root weight was responsive to P and K application for site II with a decrease in root weight, but no significant response occurred for site I. There was a significant response of tiller count to treatments for both sites, with an increase in tillers in the treated verses the control fertiliser pots. There was no statistical trend between the treatments for shoot weight, however, the control pots had the lowest shoot weight. There was no impact of gypsum on shoot weight found.</p> <p>Both sites were sampled during a drought period and the field trial was run in the break year of the drought period, so there was likely a high release of nutrients and changes in soil biology that changed the environment since the time of soil testing. Following the trial through to chickpeas, which are expected to be a more responsive crop to P and K, would be a recommended future step to build on knowledge from this trial site.</p>