Studies into the effectiveness of starter band applied phosphorus to Russet Burbank potatoes grown on ferrosol soils in Tasmania
Creators: name: Johnson, PG
Publisher: name: University Of Tasmania
Year: 2023

description: A large proportion of Tasmanian and Victorian potatoes are grown on ferrosols, which have the highest Phosphorus (P) fixing capacities of any agricultural soils in Australia. Phosphorus rates well in excess of maintenance dressings are commonly used on potato crops grown on ferrosols. This is an increasing economic cost to growers and a cost to soil and potato quality because of the significant addition to soil P and cadmium (Cd) loads. Starter fertilisers have proved successful at improving the initial P nutrition and subsequent fertiliser efficiency of crops but have not been extensively trialed with potatoes. Field trials investigating the use of starter fertilisers on cv. Russet Burbank potatoes were conducted over three years on ferrosol soils on the North West Coast of Tasmania. Granular starter bands were used in the first year and liquid starter treatments were applied in the second year. In the final year granular starter bands in combination with hill-placed dripper and standard sprinkler irrigation were trialed. The distribution of potato roots was measured and correlated with soil strength and moisture properties and the fate of irrigation water applied to the potato canopy was studied on field grown plants and by a computer model. The effects of P rate and irrigation method on ground cover development were also measured. Glasshouse and laboratory trials were conducted to investigate the effects of starter fertiliser treatments and soil conditions on plant and root growth. No starter phosphorus application improved final tuber yield. Initial petiole weight and nutrient responses were found in the first year to starter P application and from drip irrigation of conventionally banded P, but not from the starter P band. Liquid starter P improved the P nutrition of glasshouse grown plants but had no effect on early plant nutrition or final tuber yield of field grown potatoes. Subsequent glasshouse experiments indicated that higher strength liquid solutions could be used without long term injury to potato plants. Ground cover development was hastened by P applications of 100 kg P ha-1 or more and by drip irrigation in the absence of applied P. Total tuber yield was moderately correlated to ground cover measurements and there were indications that higher P applications improved the utilisation of solar radiation. There was evidence of root proliferation in the region of conventionally banded fertilisers but no indications of proliferation in the region where starter fertilisers were applied. When potato plants were left unhilled roots were able to grow out to and beyond the perimeter of the canopy. There was a prominent absence of root growth in the wheel-compacted soil of both unhilled and hilled potatoes with only sparse root growth into soil regions with bulk densities of 1.05 Mg m-3 and greater. Penetration resistance of soils with bulk density&gt; 1.1 Mg m-3 increases sharply with drying to reach strengths capable of restricting root growth. Soils of lower bulk density are unable to reach penetration resistances that could inhibit potato root growth at any moisture content. Up to 20% of the water applied to the potato canopy can be displaced laterally to the furrows giving rise to an increased water application of the furrows and a corresponding decrease in water application to the hill soil. The combined effects of water shedding from the canopy, a reduction of lateral root growth from the hilling of potatoes, and furrow compaction, have implications for irrigation efficiency and phosphorus uptake of potato crops. Potatoes were able to grow a large root system before nutrients from the sett were exhausted. Conventionally banded fertiliser at 50 mm beside and 50 mm below the sett appeared to be sufficiently close to supply P before yield-limiting P deficiency occurs. Poor root contact or unfavourable soil moisture regimes may inhibit the acquisition of nutrients from fertilisers placed with or above the sett.