Screening species and cultivars for their tolerance to acidic soil conditions.

The major phytotoxins in acid soils are aluminium and manganese. Tolerances to Al and to excessive Mn are independently inherited and Al and Mn solubilities in soils vary. In this work, the response of pasture grasses and legumes to soil acidity was studied on three soils with different Al and Mn concentrations. One provides moderate concentrations of Al with little Mn; one provides high concentrations of both Al and Mn and another provides a very high concentration of Mn at relatively low concentrations of Al. The response of a plant cultivar to changes in the soil acidity induced by lime or acid additions reflects the degree of Al and/or Mn stress provided by a particular soil, and the ability of the cultivar to tolerate those stresses. Examples are given of the way cultivars with different tolerances to Al and Mn toxicity respond to changes in acidity on the soils with different Al and Mn solubility characteristics. The utility of this screening technique to define the tolerance of cultivars to acidity on classically different soils is highlighted.     

Biological amelioration of subsoil acidity through managing nitrate uptake by wheat crops

Subsoil acidity occurs in many agricultural lands in the world, and is considered to be an irreversible constraint due to amelioration difficulties. This field study aimed to develop a biological method to ameliorate subsoil acidity through the root-induced alkalisation resulting from nitrate uptake. Aluminium (Al)-tolerant wheat variety Diamondbird and Al-sensitive variety Janz (Triticum aestivum L.) were grown at two contrasting field sites with mild and severe subsurface acidity, respectively, and were supplied with either Ca(NO₃)₂ at the soil surface, Ca(NO₃)₂ at 10 cm depth or urea at 10 cm depth. Application of nitrate increased rhizosphere pH up to 0.5 units and bulk soil pH to 0.3 units, and to a depth >30 cm in the Kandosol. The placement of nitrate at 10 cm increased subsoil pH more than the surface application. Nitrate application increased nitrate concentration in soil profiles as expected, whereas urea application increased NH ₄ ⁺ concentration which in turn favored acidification processes. Diamondbird generally produced more tillers and shoot biomass at anthesis but the two varieties did not differ in grain yield or rhizosphere alkalisation. Similar grain yields were achieved under supply of nitrate and urea. The results suggest that biological amelioration through managing nitrate uptake is possible as part of an integrated approach to combat subsoil acidity in farming systems.     

Direct determination by 2H-NMR of the ionization state of phospholipids and of a local anaesthetic at the membrane surface

Protonation and deprotonation of the primary amino group of phosphatidylethanolamine, and of the lipid phosphate groups of phosphatidylethanolamine with phosphatidylcholine, have been observed directly and isothermally in equimolar mixed fluid bilayers of the two phospholipids. In addition, the acid-base titration of the secondary amino group of the local anaesthetic, tetracaine, whilst partitioned into the bilayers, has also been determined. Here we show how studies by deuterium nuclear magnetic resonance of non-perturbing deuterons, specifically placed at the membrane polar-apolar interface, can give direct information about the electrostatics at a membrane surface.     

A combination of biological activity and the nitrate form of nitrogen can be used to ameliorate subsurface soil acidity under dryland wheat farming

The management of subsurface soil acidity remains a challenge. We tested the ability of calcium nitrate fertilization to force net anion uptake by wheat within acidic subsurface layers and hence its ability to increase, or at least maintain, soil pH within the acidic layer. The trials were conducted at two field sites: the moderately acidic site ran for 3 years (2006?C08) while the trial at the most acidic site was conducted for 2 years (2006?C07). Five treatments (nitrogen form and application method) were compared. Uptake efficiency of nitrogen (N) as measured by ¹⁵N was similar (at ~40 to 70%) for both urea and nitrate sources at both sites. The urea source acidified the soils (up to 0.2 pH in 3 years) whilst the nitrate form resulted in increases in soil pH (up to 0.3 pH). The increases in pH were of a similar magnitude to the acidification rate measured in a nearby long-term trial. The dry matter production and grain yield in our trials were compromised by the decade long drought in our region, so the work should be repeated during wetter seasons. Calcium nitrate fertilization is a useful tool for at least maintaining soil pH, and even reversing soil acidification, in acidic subsurface soil layers.