Development of key soil health indicators for the Australian banana industry

To improve the sustainability and environmental accountability of the banana industry there is a need to develop a set of soil health indicators that integrate physical, chemical and biological soil properties. These indicators would allow banana growers, extension and research workers to improve soil health management practices. To determine changes in soil properties due to the cultivation of bananas, a paired site survey was conducted comparing soil properties under conventional banana systems to less intensively managed vegetation systems, such as pastures and forest. Measurements were made on physical, chemical and biological soil properties at seven locations in tropical and sub-tropical banana producing areas. Soil nematode community composition was used as a bioindicator of the biological properties of the soil. Soils under conventional banana production tended to have a greater soil bulk density, with less soil organic carbon (C) (both total C and labile C), greater exchangeable cations, higher extractable P, greater numbers of plant-parasitic nematodes and less nematode diversity, relative to less intensively managed plant systems. The organic banana production systems at two locations had greater labile C, relative to conventional banana systems, but there was no significant change in nematode community composition. There were significant interactions between physical, chemical and nematode community measurements in the soil, particularly with soil C measurements, confirming the need for a holistic set of indicators to aid soil management. There was no single indicator of soil health for the Australian banana industry, but a set of soil health indicators, which would allow the measurement of soil improvements should include: bulk density, soil C, pH, EC, total N, extractable P, ECEC and soil nematode community structure

Measuring geometric phases of scattering states in nanoscale electronic devices

We show how a new quantum property, a geometric phase, associated with scattering states can be exhibited in nanoscale electronic devices. We propose an experiment to use interference to directly measure the effect of the new geometric phase. The setup involves a double path interferometer, adapted from that used to measure the phase evolution of electrons as they traverse a quantum dot (QD). Gate voltages on the QD could be varied cyclically and adiabatically, in a manner similar to that used to observe quantum adiabatic charge pumping. The interference due to the geometric phase results in oscillations in the current collected in the drain when a small bias across the device is applied. We illustrate the effect with examples of geometric phases resulting from both Abelian and non-Abelian gauge potentials.Comment: Six pages two figure

Comparative soil phosphorus requirements of four field crops

A range of soil phosphorus levels was established at one site on a euchrozem near Kingaroy in south-east Queensland, by dispersing rates of triple superphosphate (0-480 kg P/ha) through the 0-100 mm layer. Following two cover crops to allow equilibrium between fertiliser and soil, successive crops of barley, soybean, sorghum and peanut were grown. For each plot and each crop, Mitscherlich equations were fitted to relative seed yield versus extractable soil phosphorus levels determined on soil samples taken prior to planting. Bicarbonate extractable P levels corresponding to 90% maximum seed yield for sorghum, barley, soybean and peanut were 34, 29, 18 and 10 mg/kg respectively. Relative seed yields at the low bicarbonate extractable P levels (6-8 mg/kg) of the nil applied phosphorus plots decreased in the order: peanut > > soybean > sorghum > barley. In terms of increasing ability to utilise banded phosphorus fertiliser, the crops ranked: peanut < soybean < sorghum <barley

Phosphorus sorption and phosphorus requirements of major tobacco soils in north Queensland

From phosphorus sorption curves a supernatant solution phosphorus concentration of 0.11 ppm corresponded to 90% maximum yield of field-grown tobacco. Nineteen virgin sites in the Mareeba-Dimbulah area were sampled to cover the range of major tobacco soils

Soil phosphorus tests and grain yield responsiveness of maize (Zea mays) on Ferrosols

The grain yield response of maize (Zea mays) to various rates of applied phosphorus (P) was measured at each of 17 sites in the South Burnett region of south-eastern Queensland. The soils at all sites were Ferrosols. Relative grain yield of the nil applied P treatment [100 × (yield at nil applied P/maximum yield)] was related to Colwell (0·5 M NaHCO3) extractable P (PB), CaCl2-extractable P, and equilibrium P concentration and P buffer capacity calculated from P sorption curves. Of these P measurements, PB was most highly correlated with relative grain yield (R2 = 0·94 for a linear response and plateau fit, R2 = 0·92 for a Mitscherlich fit), and the PB values at 90% maximum grain yield were 20 mg/kg for the linear response and plateau model and 32 mg/kg for the Mitscherlich equation

Effect of banded fertilizers on soil solution composition and short-term root growth. Ii. mono- and di-ammonium phosphates

A layer of mono- or di-ammonium phosphate (MAP and DAP, respectively) was placed in contact for 5 days with duplicate columns of soil at a water content equivalent to 10 kPa matric suction. This was designed to simulate the effects of banded fertilizer on soil solution composition. Five soils were used: 0-10 cm samples from a Kurosol, a Ferrosol, a Vertosol and a Kandosol, and a 50-60 cm sample from the Kandosol. After the contact period, soil sections were recovered at successive 5 mm intervals from the fertilizer layer, the last section being 45-50 mm from the layer. Soybean (Glycine max (L.) Merr.) seedlings were grown for 48 h in each section and relative root elongation was determined. Soil solution was then extracted from each section and analysed. The amount of inorganic P in the soil solution (Pi) was summed over all soil sections for each soil and each P source and was found to be correlated with distance of P movement from the simulated band (r = 0-792, P < 0-01). Of several soil chemical parameters of the control (unfertilized) soils regressed against Pi, the following showed significant (P = 0-05) negative correlations: Ca and Mg concentrations in the soil solution for Pi from both MAP and DAP, exchangeable Ca and Mg for DAP, and citrate-dithionite extractable Fe and A1 for MAP. These results suggest that adsorption (and possibly precipitation) reactions with Fe and A1 hydrous oxides contributed to the removal of Pi from solution in the presence of MAP. However, with DAP as the fertilizer source, precipitation reactions involving Ca and Mg were the predominant factors. Dissolved organic C in the soil solution increased adjacent to both DAP and MAP, with larger amounts in proximity to DAP being a consequence of the higher soil solution pH («7). Soil solution Si increased in all soils adjacent to both DAP and MAP, with concentrations being higher in the MAP treatments. Dissolution of aluminosilicates in the acidic conditions near MAP (pH˜5) was the probable cause. Relative root elongation (RRE) of soybean was restricted in soil sections close to the fertilizer. When RRE was plotted against each of soil solution EC, NH3 activity, and calcium activity ratio (CAR), a single curvilinear function described the relationship between RRE and CAR for all soils and both P sources. It is concluded that a salt-induced Ca deficiency was the cause of restricted root growth in proximity to DAP and MAP, rather than an osmotic effect or NH3 toxicity

High input sugarcane production systems can mask the adverse effects of poor soil health

Breaking the sugarcane monoculture or fumigating long-term sugarcane land enhances crop establishment. In many situations, enhanced establishment is instrumental in ultimately producing higher cane and sugar yields. However, recent studies in rotation experiments in the Burdekin have shown that with full irrigation and high inputs of nitrogen fertiliser, tillering can be increased to the extent that poor primary shoot establishment can be compensated by the production of more tillers. This results in the ultimate yield difference between breaks/fumigation and sugarcane monoculture being substantially reduced. The relatively good yields that can be produced with sugarcane monoculture in the Burdekin has led to a general conclusion that yield decline (poor soil health) is not an important issue in this region. However, research by the SYDJV has shown that soil health is as much an issue in the Burdekin as anywhere else, but the ultimate effect on crop yield can be masked by irrigation and high inputs of nitrogen fertiliser. The results of this research emphasise several important implications associated with management of high input systems. Although the adverse effects of poor soil health can be masked, the long-term consequences of ignoring soil health need to be seriously considered. Further, the excessive use of resources such as nitrogen fertiliser and irrigation water, have both economic and environmental consequences. In this paper we demonstrate that yields can be maintained with lower inputs in situations where soil health has been maintained through rotation breaks and the build-up of soil carbon (organic matter) levels. Further, it is argued that substituting high inputs to mask the effects of poor soil health is very much against the development of more sustainable sugarcane farming systems