The fate and availability of P derived from granular fertilisers in an alkaline Calcarosol soil were examined in a 65-year field trial in a semi-arid environment (annual rainfall 325 mm). Sequential P fractionation was conducted in the soils collected from the trial plots receiving 0-12 kg P ha −1 crop −1 , and the rhizosphere soil after growing wheat (Triticum aestivum L. cv. Yitpi) and chickpea (Cicer arietinum L. cv. Genesis 836) for one or two 60-day cycles in the glasshouse. Increasing long-term P application rate over 65 years significantly increased all inorganic P (Pi) fractions except HCl-Pi. By contrast, P application did not affect or tended to decrease organic P (Po) fractions. Increasing P application also increased Olsen-P and resin-P but decreased the P buffer capacity and sorption maxima. Residual P, Pi and Po fractions accounted for an average of 32, 16 and 52% of total P, respectively. All soil P fractions including residual P in the rhizosphere soil declined following 60-day growth of either wheat or chickpea. The decreases were greater in soils with a history of high P application than low P. An exception was water-extractable Po, which increased following plant growth. Changes in various P fractions in the rhizosphere followed the same pattern for both plant species. Biomass production and P uptake of the plants grown in the glasshouse correlated positively with the residual P and inorganic fractions (except HCl-Pi) but negatively with Po in the H 2 O-, NaOHand H 2 SO 4 -fractions of the original soils. The results suggest that the long-term application of fertiliser P to the calcareous sandy soil built up residual P and nonlabile Pi fractions, but these P fractions are potentially available to crops.

We have investigated the control preparation and aqueous stability of a potential suspension fertilizer: zinc hydroxide nitrate. We have observed that this compound can be synthesized by quick precipitation of zinc nitrate in sodium hydroxide solution under various conditions, whereas it can also be readily transformed to more stable Zn(OH) 2 or ZnO at pH >6.5 and aged at 50 °C. The transformation from zinc hydroxide nitrate to Zn(OH) 2 and ZnO has been examined with XRD/FTIR/SEM techniques and discussed in detail, presumably involving the formation and dissociation of the intermediate solution species [Zn(OH) 4 ] 2− /[Zn(OH) 3 ] − . We have also found that as-prepared zinc hydroxide nitrate crystals are very stable when they are isolated and then dispersed in aqueous solution with pH 5−9 while slightly dissolved to give zinc ion concentration of 30−50 mg/L. Such aqueous stability and solubility have thus suggested that this compound can be used as a long-term zinc foliar fertilizer of various crops.

Background, aim, and scope Despite the contribution of many sequential P fractionation schemes to the study of P transformations in agricultural soils, the nature of P in each fraction remains qualitative rather than mechanistic. This study used the sequential extraction and isotopic dilution techniques to assess the recovery of a tracer ( 32 P) in soil P fractions and to elucidate the transformation of soil P in different P pools and its lability. Materials and methods Three contrasting soils (Vertosol, Calcarosol, and Chromosol) were collected from paddocks with a long history of P fertilization and from an adjacent virgin area under native vegetation. The soils were labeled with 32 P and then incubated for differing periods before being sequentially extracted for P fractions. Recovery of 32 P in each P fraction was measured. Results The P history increased total and available P in all soils but decreased phosphorus buffering capacity only in the Calcarosol. The previously applied P was distributed into all Pi fractions, and the proportion of the P transformed into individual fractions depends on soil characteristics. Adding P significantly increased the 32 P recovery in the water-Pi fraction of the Calcarosol. In contrast, the higher proportion of the label was recovered in the bicarbonate-Pi of the Vertosol and in the NaOH-Pi of the Chromosol. Discussion The recovery of 32 P in all soil P fractions showed that 32 P had undergone exchange with the native P. The exchange reaction was most dominant in the Pi fractions. The greater level of the 32 P recovered in the water-Pi fraction of the P-amended Calcarosol indicates that the added P transformed into this fraction remains highly exchangeable. In contrast, the significantly greater amount of 32 P recovered in the NaOH-Pi fraction of the Chromosol suggests that this fraction is of great importance in P fertility of this soil type. Conclusions The transformation of soil P fraction was dependent on soil type and P fertilization history. However, during the short-term (42 days), the applied P preferably remained in the form that can be exchangeable with solution P and, therefore, can be plant-available. Recommendations and perspectives Long-term history of P fertilization has resulted in P accumulation which is associated with an increased P availability and decreased sorption. The fertilizer P is shown to distribute into all the P fractions. Further studies are warranted to examine the accessibility of these P fractions by plants. The isotopic dilution technique using 32 P has been verified to be useful for quantifying P transformation and contributes to a further understanding of P dynamics in native and farming systems.

Highlights-Zn uptake by N. caerulescens tranlocated to leaves.-Great ability of young N. caerulescens plants to accumulate Zn in shoots.-Decrease of Ca and P concentration with increasing amount of Zn treated.-Zn crystals found in leaf epidermal cells and root cortex of N. caerulescens.-In the plant tissues, P and S co-localized while Ca localized with Zn. AbstractUnderstanding the uptake mechanisms of heavy metals by hyperaccumulators is necessary for improving phytoextraction options to reduce metal toxicities in contaminated soils. In this study, the capacity of Zn uptake by the hyperaccumulator Noccaea caerulescens was investigated and compared to the non-hyperaccumulator Thlaspi arvense. The plants were grown under hydroponic conditions in a glasshouse. The distribution of Zn in the roots and leaves of these species was investigated by scanning electron microscopy with energy-dispersive X-ray analysis. Compared with the control with no Zn added, it was shown that prolonged Zn treatments decreased the biomass of both N. caerulescens and T. arvense. Since N. caerulescens requires Zn for growth, no Zn toxicity symptoms were observed, even when the Zn A C C E P T E D M A N U S C R I P T concentration in shoots reached 2.5% dry mass. T. arvense showed serious Zn toxicity only after two weeks of Zn treatment. Zn uptake by N. caerulescens was mainly translocated to the leaves while almost all of the Zn taken-up by T. arvense was retained in the roots. In N. caerulescens, increased concentrations of Zn in the shoots resulted in reductions in Ca and P concentrations by up to 50% and 35%, respectively. Zn-containing crystals were abundant in both the upper and lower epidermal cells of the leaves and in the cortex of the roots during the later growth phase.Co-localization of Ca and Zn, P and S were found in leaf and root tissues. The results suggest that Zn-rich crystals with an abundance of the Zn ligand in the roots and shoots, and colocalization and interaction between Zn and other ions, may have functional significance with respect to conferring particular attributes to N. caerulescens that are not present in the nonhyperaccumulator counterpart. An understanding of these species-specific differences has relevance from the perspective of offering some insight into how particular species could contribute to a strategy for the detoxification of Zn-contaminated sites.

Major changes in tillage practices have occurred over the past 2 decades across the diverse range of soil types and rainfall zones that characterise cropping systems in southern Australia. However, there has been little corresponding change in the management of nutrients, especially phosphorus (P). This study investigated the effects of tillage and crop rotations on the stratification and transformation of P in soil profiles from 3 tillage/rotation trials encompassing 3 agro-ecological zones of southern Australia. Soil samples were collected from field trials at Longerenong (Vertosol, average rainfall 420 mm), Walpeup (Calcarosol, rainfall 325 mm), and Rutherglen (Chromosol, rainfall 650 mm) in Victoria. Soil samples from various depths were sequentially analysed for organic and inorganic P fractions. Phosphorus accumulated in the surface soil (0–0.1 m) across all sites and tillage practices/rotations studied but the proportion of P in different chemical fractions varied markedly among soil types and tillage practice/rotation. In the sandy Calcarosol, a greater proportion of fertiliser P was transformed into labile (resin-P) forms, whereas it tended to accumulate in non-labile pools in the finer textured Vertosol and Chromosol. The effects of tillage and crop rotation were generally confined to the topsoil with P strongly stratified in the topsoil in direct-drill and zero-tillage treatments compared with conventional tillage. The implications for management of P fertilisers in Victorian cropping systems are discussed.