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While soil salinization is a major concern for agriculture worldwide, the application of sodium (Na) can stimulate growth in many plant species, due to its ability to replace potassium (K) in some physiological functions. We present an overview of the potential and risks associated with replacing KCl fertilizer with a mixture of KCl and NaCl in tropical plantations, with a focus on Eucalyptus. A wide range of responses of Eucalyptus species to the salinization of the soil is well documented and the planting of Eucalyptus rows in salinity-damaged landscapes has been used in Australia to lower the water table and reduce soil salinization. A positive effect of NaCl application on Eucalyptus growth in K-deficient environments has been demonstrated in hydroponics, which is consistent with comprehensive studies conducted on entire rotations in Brazil. The addition of NaCl to K-deficient soils increased above-ground biomass at harvest in E. grandis plantations by a factor of 1.4, whereas the addition of the same amount of KCl increased biomass by a factor of 2. A comparison between KCl and K 2 SO 4 applications suggested a positive response of E. grandis to Cl, in addition to the response to Na. The effects of Na application on the physiology of E. grandis support the hypothesis of a functional role for Na in K-deficient soils. Consistent results have been reported on the physiology of olive tree, coconut palm and cocoa tree. Atmospheric inputs of Na depend on the distance from the ocean, ranging from approximately 30 to 5 kg ha-1 yr-1 in coastal and inland forests, respectively. Na is an essential nutrient for animals, maintaining homeostasis and playing a crucial role in neural networks. Substantial quantities of Na are routinely fed to animals in extensive livestock farming. A growing body of evidence suggests that a shortage of Na can limit the activity of insects, particularly plant decomposers. The application of Na in tropical plantations could therefore accelerate the release of nutrients during litter decomposition, thereby promoting tree growth. However, Na application could also stimulate herbivory and lead to leaf area losses. We recommend setting up multi-location experiments covering a wide range of soils and climates in tropical regions, for perennial species of commercial interest. In-depth studies should be carried out on certain sites to understand how tree physiology, soil functioning and herbivory are influenced by the addition of NaCl. • The application of NaCl greatly enhances Eucalyptus growth in K-deficient soil. • Consistent results were reported for Eucalyptus , coconut, olive and cocoa trees. • A shortage of Na can limit insect activity and influence litter decay and herbivory. • Multi-site experiments are needed to understand the response of perennial species. [ABSTRACT FROM AUTHOR]

An improved ability to predict pasture dry matter (DM) yield response to applied phosphorus (P), potassium (K) and sulfur (S) is a crucial step in determining the production and economic benefits of fertiliser inputs and the environmental benefits associated with efficient nutrient use. The adoption and application of soil testing can make substantial improvements to nutrient use efficiency, but soil test interpretation needs to be based on the best available and most relevant experimental data. This paper reports on the development of improved national and regionally specific soil test–pasture yield response functions and critical soil test P, K and S values for near-maximum growth of improved pastures across Australia. A comprehensive dataset of pasture yield responses to fertiliser applications was collated from field experiments conducted in all improved pasture regions of Australia. The Better Fertiliser Decisions for Pastures (BFDP) database contains data from 3032 experiment sites, 21 918 yield response measures and 5548 experiment site years. These data were converted to standard measurement units and compiled within a specifically designed relational database, where the data could be explored and interpreted. Key data included soil and site descriptions, pasture type, fertiliser type and rate, nutrient application rate, DM yield measures and soil test results (i.e. Olsen P, Colwell P, P buffering, Colwell K, Skene K, exchangeable K, CPC S, KCl S). These data were analysed, and quantitative non-linear mixed effects models based upon the Mitscherlich function were developed. Where appropriate, disparate datasets were integrated to derive the most appropriate response relationships for different soil texture and P buffering index classes, as well as interpretation at the regional, state, and national scale. Overall, the fitted models provided a good fit to the large body of data, using readily interpretable coefficients, but were at times limited by patchiness of meta-data and uneven representation of different soil types and regions. The models provided improved predictions of relative pasture yield response to soil nutrient status and can be scaled to absolute yield using a specified maximal yield by the user. Importantly, the response function exhibits diminishing returns, enabling marginal economic analysis and determination of optimum fertiliser application rate to a specific situation. These derived relationships form the basis of national standards for soil test interpretation and fertiliser recommendations for Australian pastures and grazing industries, and are incorporated within the major Australian fertiliser company decision support systems. However, the utility of the national database is limited without a contemporary web-based interface, like that developed for the Better Fertiliser Decisions for Cropping (BFDC) national database. An integrated approach between the BFDP and the BFDC would facilitate the interrogation of the database by advisors and farmers to generate yield response curves relevant to the region and/or pasture system of interest and provides the capacity to accommodate new data in the future. Optimising phosphorus, potassium and sulfur fertiliser applications to pasture will improve the productivity of grazing industries as well as environmental outcomes. The compilation and utilisation of extensive national field studies has enabled soil test interpretation to be based on the best available and most relevant experimental data. The derived critical soil test P, K and S targets have improved fertiliser recommendations for improved pastures in Australia. [ABSTRACT FROM AUTHOR]

Grain yield increases (responses) of canola (oilseed rape, Brassica napus L.) and spring wheat (Triticum aestivum L.) to application of nitrogen (N) and potassium (K) fertilizers were compared in the same experiment at eight field sites over three years (2000-2002) in southwestern Australia. Four rates of N (0-138 kg N/ha as urea) and four rates of K (0-60 kg K ha-1 as potassium chloride) were applied. Significant grain yield responses to applied N and K occurred for both crop species at all sites of the experiment, and the NxK interaction was significant. Canola required an average of 26% more applied N and 32% more applied K than wheat to produce 90% of the maximum grain yield. Applying increasing rates of K increased the rate of N required for 90% of maximum grain yield. Likewise, applying increasing rates of N increased the rate of K required for 90% of the maximum grain yield. Fertilizer K had no significant affect on the concentration of oil in canola grain or concentration of protein in both canola and wheat grain. Application of increasing rates of N decreased the concentration of oil while increasing the concentration of protein in canola grain, and increased concentration of protein in wheat grain. The NxK interaction was not significant for concentration of oil or protein in grain. [ABSTRACT FROM AUTHOR]

Rain-fed dairy pastures on sandy soils common in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise the annual species subterranean clover (Trifolium subterraneumL.) and annual and Italian ryegrass (Lolium rigidumGaud. and L. multiflorumLam.). In wet years, clover becomes potassium (K) deficient and shows large dry matter (DM) responses to applied fertiliser K due to leaching of K in soil by rainfall. In contrast, ryegrass rarely shows DM responses to applied K. Many dairy pastures in the region are now intensively grazed to maximise pasture use for milk production, and nitrogen (N) fertiliser is applied after each grazing. It is not known if frequent applications of fertiliser N to these pastures changes pasture DM responses to applied K. Therefore, a long-term (2002–07) field experiment was undertaken on an intensively grazed dairy pasture in the region to quantify pasture DM responses to applied fertiliser K with or without applications of adequate fertiliser N (141–200 kg N/ha per year). Soil samples (top 10 cm of soil) were collected from each plot of the experiment each February to measure soil test K by the standard Colwell sodium bicarbonate procedure used for both K and phosphorus soil testing in the region.When no N was applied, pasture comprised ~70% (dry weight basis) clover and 25% ryegrass, compared with ~70% ryegrass and 25% clover when adequate N was applied. Significant linear responses of pasture DM to applied K occurred in 3 of the 6 years of the experiment only when no N was applied and clover dominated the pasture. The largest response varied from ~1.7 to 2.0 t/ha DM consumed by dairy cows at all grazings in each year, giving a K response efficiency of between 8 and 10 kg DM/ha per kg K/ha applied. Significant pasture DM responses to applied N occurred at all grazings in each year, with ~2–3 t/ha extra DM consumed by dairy cows at all grazings in each year being produced when a total of 141–200 kg N/ha was applied per year, giving an N response efficiency of ~7–19 kg DM/ha per kg N/ha applied. Soil test K values were very variable, attributed to varying proportions of soil samples per plot collected between and within cow urine patches, containing much K, arbitrarily deposited on experimental plots during grazing. Soil test K values were not significantly affected by the rates of K applied per year. A re-evaluation of results from the major soil K test study conducted for pastures in the region confirm that ryegrass rarely showed DM responses to applied K, and that for clover, soil K testing poorly predicted the likelihood of K deficiency in the next growing season. [ABSTRACT FROM AUTHOR]