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The transition from mining to agriculture is hampered by a range of abiotic challenges to crop growth, including nutritional issues and heavy metal stress. Building on our previous work showing that potassium (K) limits legume growth in post-phosphate mining substrates on tropical Christmas Island, Australia, we undertook two field trials. The first compared the efficacy of controlled release K fertilisers (CRFs: KCl 2-month release, K2SO4 3-month and K2SO4 9-month) with immediately available potassium sulfate (K2SO4) fertiliser, on the legume Lablab purpureus. The second trial tested responses of L. purpureus to different rates of K2SO4 9-month CRF, and a combination treatment (CRF and K2SO4). Both trials were undertaken to determine how CRFs compare with immediately available K2SO4 in terms of increasing biomass, reducing cadmium (Cd) concentrations, maximising plant K concentrations and maintaining K soil retention. The first trial revealed that K2SO4 3-month and 9-month CRFs were similar to the 160 kg/ha K2SO4 treatment in significantly increasing L. purpureus biomass. Plant Cd and other heavy metal concentrations were significantly lower as plant biomass increased with increasing K, including with CRFs. The second trial showed no difference between various rates of K2SO4 9-month CRF and immediately available 160 kg/ha K2SO4 to increase biomass, reduce Cd or increase K concentrations. We have shown that although post-phosphate mining substrates can limit legume growth, high biomass can be attained with some CRFs, or K2SO4 at 160 kg/ha. Optimising nutrient input in post-mining agriculture is critical for developing safe, sustainable crops.

Zeolite is an abundant potassium (K)-rich silicate mineral that could increase K supply to plants. Potassium deficiency causes lodging problems and yield reductions in paddy fields in China. However, it is unknown whether zeolite amendments alleviate K deficiency or enhance lodging-related stem morphology characteristics in rice. A 2-year field experiment was conducted to evaluate the effect of zeolite amendment (0, 5 and 10 t ha–1) and K application (0, 30 and 60 kg ha–1) on rice grain yield, stem morphology, and K nutrient status in soil and plant tissues. In both years zeolite and K application, alone or in combination, significantly increased grain yield, mainly through increased number of panicles per plant with zeolite application and number of spikelets per panicle with K application. In the top 30 cm soil layer, zeolite amendment increased cation exchange capacity by up to 31% and available K by up to 38%. Zeolite or K application alone significantly increased stem, leaf and panicle K concentrations. Zeolite promoted K allocation to rice stems, and improved stem morphology associated with lodging index. In both years, zeolite or K application alone increased stem diameter, dry weight linear density and the breaking resistance moment by up to 7.0%, 8.3% and 16%, respectively, and decreased the stem lodging index by up to 6.7%. In summary, zeolite is an alternative source of K fertiliser and can alleviate K deficiency in paddy fields in China and elsewhere.

Uptake of potassium (K) in crops depends mainly on the root system. Field, pot and hydroponic experiments were carried out to characterise root morphological traits and examine their roles in K uptake and utilisation of vegetable soybean (edamame) (Glycine max (L.) Merr.). Of 40 genotypes, two high K-efficiency (HKE) and two low K-efficiency (LKE) genotypes were identified and compared at two levels of K application: nil or 120 kg K2SO4 ha–1. HKE genotypes had shorter total root length and smaller root surface area and root volume than LKE genotypes, but responded earlier to low-K conditions by adjusting root architecture. In plants receiving nil K, total root length was increased by 10.4–21.8% for HKE genotypes but decreased by 5.5–9.5% for LKE genotypes at the V4 stage relative to plants receiving applied K. HKE genotypes were more efficient in redistributing K from source to sink tissue, especially from leaf. Of the total K in vegetative tissues, 35.0–46.4% was redistributed to seed in HKE genotypes, whereas only 19.7–28.2% was redistributed in LKE genotypes. HKE genotypes also had a higher specific K uptake rate (K uptake per unit root length), 1.6–1.7 times higher than LKE genotypes at the R5 stage. This indirectly indicated a stronger root K acquisition in HKE genotypes. This study suggests that future vegetable soybean improvement with greater K efficiency should be focused on the selection of higher K-redistribution rate and specific K-uptake rate.

Rooted single leaves of sweet potato (Ipomoea batatas L.) produce and translocate photosynthates, thus representing an ideal model for characterising the source–sink relationships and responses to various environments. A hydroponics culture study was conducted with rooted single leaves of sweet potato to determine intraspecific variation in growth, biomass partitioning, and associated physiological changes in response to variable potassium (K) supply among genotypes Ji22 (low K-use efficiency), Nan88 (high K-uptake efficiency) and Xu28 (high K-use efficiency). Potassium deficiency suppressed biomass accumulation in blades, petioles and roots in all three genotypes. Root length of diameters

The differences in the transport characteristics in planta between potassium (K+) and caesium (Cs+) was investigated using their radionuclides, 42K+ and 137Cs+. A tracer experiment using nutrient solutions supplemented with 42K and 137Cs revealed that the ratio of the root’s K+ uptake rate to its Cs+ uptake rate was 7–11 times higher than the K+ : Cs+ concentration ratio in the solution, and the number was varied depending on the K concentration in the solution and also on the growth condition. After entering through the root tissues, the 42K+ : 137Cs+ ratio in the shoots was 4.28 times higher than the value in the roots. However, the 42K+ : 137Cs+ ratio in each leaf did not differ significantly, indicating that the primary transport of K+ and Cs+ in the shoots are similarly regulated. In contrast, among the radionuclides stored in the roots over 4 h, 30% of the 42K+ was exported from the roots over the following hour, whereas only 8% of 137Cs+ was exported. In addition, within the xylem, K+ was shown to travel slowly, whereas Cs+ passed quickly through the roots into the shoots. In conclusion, our study demonstrated very different transport patterns for the two ions in the root tissues.

Potassium (K) is one of the limiting factors that negatively influenced rice growth and yield in submergence-prone soils. We conducted an experiment during the wet season of 2014–15 to achieve optimal doses of K and understand the effect of K application on submerged rice in terms of survival, chlorophyll content, non-structural carbohydrates (NSC), anti-oxidant activities and yield. Results revealed that chlorophyll and NSC content were significantly (P ≤ 0.05) lower whereas the activity of anti-oxidants (catalase, superoxide dismutase and total peroxidase) were significantly (P ≤ 0.05) higher after submergence compared with pre-submergence. Further, application of K at a higher basal dose (40 kg ha–1) was more beneficial to improve survival after de-submergence by maintaining NSC, chlorophyll content and higher activity of anti-oxidants with lower level of lipid peroxidation. Furthermore, results showed superiority of the treatments having application of higher doses with one foliar spray (T9–40 kg K2O ha–1 (basal) + one foliar spray at 0.5% K at panicle initiation (PI) stage) for grain yield. We conclude that application of a higher dose of K with one foliar application at PI stage is more beneficial to enhance plant survival, better recovery and yield gain of rice during complete submergence.

Movement of species outside their range of distribution could be a strategy for conservation purposes, but before implementation, it is necessary to evaluate plants responses to the conditions that they will experience in new locations. We evaluated the effect of potassium fertilisation to enhance the frost tolerance of young individuals of Albizia plurijuga (Standley) Britton & Rose, Cedrela dugesii S.Watson and Ceiba aesculifolia (Kunth) Britten & Baker f., which are all common species from tropical dry forests in Mexico. Plants were propagated in a shade-house and fertilised during 9 months with different concentrations of potassium (39, 189 and 528 ppm). In frost simulations, plants were exposed to temperatures below 0°C during different time periods and frost injury was assessed by electrolyte leakage of leaf discs from young and old leaves. We observed that potassium fertilisation enhanced frost tolerance by reducing electrolyte leakage mainly in young leaves. We recorded plant re-sprouting ability after exposure to subzero temperatures over 45 days, finding notable differences among species: all individuals of C. dugesii sprouted, followed by some of A. plurijuga and finally just one of C. aesculifolia. Also, high potassium levels increased re-sprouting response. These species have a low frost tolerance, but potassium fertilisation seemed to be effective to enhance it for young individuals, increasing the probability of survival if plants are moved to colder areas than current habitats.

Cultivars with higher potassium utilisation efficiency (KUtE) are likely to have superior photosynthesis (A) under K deficiency. However, the inner link between KUtE and photosynthesis remains unclear. A quantitative analysis of stomatal (SL), mesophyll conductance (MCL) and biochemical (BL) limitations on A in response to K supplementation was performed on upper and lower leaves of Brassica napus L. Huayouza No. 9 (H9, high KUtE) and Zhongshuang No. 11 (Z11, low KUtE). Both cultivars showed remarkable improvement in leaf area and lower leaf photosynthesis with elevated K supply. The total photosynthetic limitation of Z11 in lower leaf was 51.9% higher than that of H9 under K deficiency. Most of limitation under K deficiency was dominated by MCL for Z11, yet it was equally controlled by MCL and SL for H9. Nevertheless, with increasing K supply, SL became the primary limitation for both cultivars. Z11 needed a 12.0% higher leaf K concentration to avoid A decline, and higher K-based thresholds for each limitation. Overall, cultivars higher in KUtE have improved inherent leaf photosynthesis and area, and present lower K-based thresholds for SL, MCL and BL.

The aim of this study was to determine the effect of potassium (K) supplementation on the calcium (Ca) absorption capacity from the rumen and abomasum of sheep. The Ca absorption capacity from the rumen and abomasum of sheep was measured using stable strontium (Sr) as a Ca-analogue tracer method. The sheep, cannulated at either the rumen or abomasum, were randomly allocated to one of two groups (control or K-supplemented) and fed in individual metabolism pens twice daily with a diet comprising oaten hay, lucerne chaff and barley fortified with or without potassium carbonate (K2CO3). The K content of the diet of the K-supplemented animals was 3.1% of dry matter compared with 1.4% for the control animals. The animals were fed their respective diets for a period of 2 weeks. The fractional absorption capacity (FC) of Ca was estimated before, during and after the treatment period. Supplementation with K decreased the FC of Ca in both the rumen and abomasum during treatment and increased the FC of Ca in the abomasum post-treatment. Supplementation with K also increased the fractional excretion of K in the urine, but decreased the fractional excretion of Ca and magnesium (Mg) (P < 0.05), showing that K supplementation significantly affected Ca and Mg metabolism. Results suggest that renal conservation of Ca and Mg is an important mechanism controlling the Ca and Mg pool for vital functions of the body. In times of high demand for these minerals during lactation and pregnancy, high K in the diets may predispose sheep to hypomagnesaemia and hypocalcaemia, which in turn will have a negative impact on productivity and economic returns.

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, 21918 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.

SsHKT1;1, a HKT1 homologue, was isolated from the C3 halophyte Suaeda salsa L. and its ion transport properties were investigated in heterologous systems. The expression of SsHKT1;1 suppressed a K+ transport-defective phenotype of the yeast strain CY162 (Δtrk1Δtrk2), suggesting the enhancement of K+ uptake with SsHKT1;1. However, it did not suppress the salt-sensitive phenotype of the yeast strain G19 (Δena1–4), which lacks a major component of Na+ efflux. Transgenic Arabidopsis thaliana (L.) Heynh. plants overexpressing SsHKT1;1 showed enhanced salt tolerance and increased shoot K+ concentration, whereas no significant changes in shoot Na+ concentration were observed. S. salsa was also used to investigate K+ uptake properties under salinity. The K+ transporters in the roots selectively mediated K+ uptake irrespective of external Na+ and their inhibitor did not affect Na+ uptake at low K+. Thus, both molecular and physiological studies provide strong in vivo evidence that SsHKT1;1 mainly acts as a potassium transporter in heterologous expression systems and S. salsa, and that it is involved in salt tolerance by taking part in the maintenance of cytosolic cation homeostasis, particularly, in the maintenance of K+ nutrition under salinity.

In the agricultural lands of south-western Australia, salinity severely affects about 1 million hectares, and there is also widespread occurrence of potassium (K) deficiency. This study investigated whether the effects of sodium (Na) on crop K nutrition vary with plant salt sensitivity. In a glasshouse experiment with loamy sand, two barley cultivars (Hordeum vulgare L. cv. Gairdner, salt sensitive, and cv. CM72, salt tolerant) and one wheat cultivar (Triticum aestivum L. cv. Wyalkatchem, salt tolerant) were first grown in soil containing 30 mg extractable K/kg for 4 weeks to create mildly K-deficient plants, then subjected to Na (as NaCl) and additional K treatments for 3 weeks. Although high Na (300 mg Na/kg) reduced leaf numbers, moderate Na (100 mg Na/kg) hastened leaf development in barley cultivars but not in wheat. In the salt-tolerant CM72, moderate Na also increased tiller numbers, shoot dry weight and Na accumulation, but not root growth. The positive effect of moderate Na on shoot growth in CM72 was similar to that of adding 45 mg K/kg. Root growth relative to shoot growth was enhanced by adequate K supply (75 mg K/kg) compared with K deficiency, but not by Na supply. Soil Na greatly reduced the K/Na and Ca/Na ratios in shoots and roots, while additional K supply increased the K/Na ratio with little effect on the Ca/Na ratio. The study showed that the substitution of K by Na in barley and wheat was influenced not only by plant K status, but by the potential for Na uptake in roots and Na accumulation in shoots, which may play a major role in salt tolerance. The increased growth in shoots but not roots of salt-tolerant CM72 in response to moderate Na and the greater adverse effect of soil K deficiency on roots than shoots in all genotypes would make the low-K plants more vulnerable to saline and water-limited environments.

The effectiveness of exogenous application of K in ameliorating the adverse effects of waterlogging on cotton plants was assessed under greenhouse conditions. Forty-day-old plants were subjected to continuous flooding for 1 week and then K (60 kg ha–1) was applied either as soil application, foliar spray, or in combination. The waterlogging treatment significantly reduced plant height and fresh and dry biomass, photosynthetic pigments, gas exchange parameters and nutrient accumulation (N, K+, Ca2+) in stem, root and leaves of cotton plants, Although Mg2+ content in roots increased significantly due to waterlogging, it was not affected in stem or leaves. In contrast, Mn2+ and Fe2+ contents generally increased under waterlogged conditions. All water relation parameters were also significantly influenced by waterlogging stress. Waterlogged plants supplemented with K showed a significant improvement in growth, photosynthetic pigments and photosynthetic capacity. Potassium supplementation also improved nutrient uptake of waterlogged plants and resulted in significantly higher accumulation of K+, Ca2+, N, Mn2+ and Fe2+ than those plants not supplied with K. Although all modes of K application were effective in mitigating the inhibitory effects of waterlogging, the combined application through soil + foliar spray yielded the best results and the foliar application (alone) being the least effective.

A novel approach to the sustainable management of potassium (K) resources in agro-ecosystems is through better exploitation of genetic differences in the K efficiency of crop plants. Potassium efficiency is a measure of genotypic tolerance to soils with low potassium availability and can be quantified as the K efficiency ratio (the ratio of growth at deficient and adequate K supply). This study investigated the magnitude of variation in K efficiency among wheat (Triticum aestivum L.) genotypes grown in a glasshouse and in the field. Genotypes differed significantly in response to low soil K availability in terms of shoot biomass during the vegetative growth phase and grain yield at maturity under glasshouse (144 genotypes) and field (89 genotypes) conditions. K-efficient and K-inefficient genotypes were identified. The main factor determining K efficiency for grain yield was the capacity of genotypes to maintain a high harvest index (grain yield/total shoot weight) at deficient K supply. Genotypes that had reduced harvest index under deficient K supply were K-inefficient. Capacity to tolerate low concentrations of K in shoot tissue where K supply was deficient was also important in determining K efficiency for grain yield. Potassium-efficient genotypes have the potential to enhance the productivity and sustainability of cereal cropping systems.

Most soils used for agriculture in south-western Australia are sandy and are now deficient in both potassium (K) and nitrogen (N) for cereal and canola (oilseed rape; Brassica napus L.) grain production. However, the effect of applying different levels of both fertiliser K and N on grain yields of these crops is not known. We report results of 10 field experiments, conducted on sandy soils in the region, to measure the effects of applying both K and N on canola grain yields and concentration of oil and protein in grain. Four levels of K (0–60 kg K/ha as potassium chloride) and four levels of N (0–138 kg N/ha as urea) were applied. Significant grain yield responses to applied N occurred in all experiments for the nil-K treatment and each level of K applied, with responses increasing as more N was applied. For all levels of N applied, significant grain yield responses occurred when up to 30 kg K/ha was applied, with no further significant grain yield responses occurring when 60 kg K/ha was applied. The K × N interaction was always significant for grain production. Application of K had no effect on the concentration of oil and protein in grain. Application of N consistently decreased concentration of oil and increased concentration of protein in grain. The K × N interaction was not significant for concentration of oil or protein in grain, but application of up to 30 kg K/ha significantly increased canola grain and so oil yields (concentration of oil in grain multiplied by grain yield). Our results are likely to be relevant for all acidic to neutral sandy soils worldwide used for growing canola crops.

Salinity is a problem facing many crop and livestock producers in southern Australia. One management option is to revegetate with salt-tolerant plants suitable for animal production. These plants are often halophytic shrubs containing up to 30% ash, predominantly as sodium, potassium, or chloride. This experiment examines the consequences of a high intake of sodium and potassium separately or together on feed intake, digestibility, liveweight change, and wool growth. Twelve groups of 6 weaner wethers were allocated to treatments according to a balanced 3 × 4 factorial design with 3 levels of added potassium (0, 0.38, and 0.77 mol/kg DM equivalent to 0, 15, and 30 g/kg DM) and 4 levels of added sodium (0, 0.87, 2.18, and 3.48 mol/kg DM, equivalent to 0, 20, 50, and 80 g/kg DM) as the chloride salts. The treatment diets were fed to sheep for 6 weeks. Increasing sodium in the diet significantly decreased feed intake, digestibility, liveweight gain, and wool growth either as a main effect or through an interaction with potassium. Organic matter intake was reduced from 1.35 kg at the lowest levels of sodium and potassium to 0.67 kg at the highest levels. Comparing the same 2 groups, liveweight gain was reduced from 144 to 0 g/day, organic matter digestibility from 59.1% to 57.3%, and wool growth from 1.21 to 1.04 mg/cm2.day. The response surfaces indicate that production was depressed even at the lower levels of sodium, whereas high potassium depressed intake, digestibility, and liveweight gain at high levels of sodium only. The interaction between sodium and potassium was always negative at high levels of sodium, indicating that manipulation of the proportions of the 2 elements is unlikely to provide benefits for animal production when total salt levels are high. Although wool growth was depressed at high sodium and potassium, the efficiency of wool growth increased from 10.0 to 15.4 g/kg organic matter intake when the lowest and highest levels of the sodium and potassium were compared. This result may present significant opportunities for the use of saline land to grow fine wool.

Dairy and beef pastures in the high (>800 mm annual average) rainfall areas of south-western Australia, based on subterranean clover (Trifolium subterraneum) and annual ryegrass (Lolium rigidum), grow on acidic to neutral deep (>40 cm) sands, up to 40 cm sand over loam or clay, or where loam or clay occur at the surface. Potassium deficiency is common, particularly for the sandy soils, requiring regular applications of fertiliser potassium for profitable pasture production. A large study was undertaken to assess 6 soil-test procedures, and tissue testing of dried herbage, as predictors of when fertiliser potassium was required for these pastures. The 100 field experiments, each conducted for 1 year, measured dried-herbage production separately for clover and ryegrass in response to applied fertiliser potassium (potassium chloride). Significant (P100 mg/kg soil. There was always a clover-yield increase to applied potassium for Colwell potassium at 50 and

Summary. Critical potassium (K) concentrations for the diagnosis of K deficiency were determined in various shoot parts of faba bean (Vicia faba L. cv. Fiord) and chickpea (Cicer arietinum L. T1587) plants grown at K rates of 0–240 mg K/kg in a K-deficient soil in the glasshouse. Shoot growth of both species increased with rates of K applied and with plant age but faba bean was more responsive to K application than chickpea. Potassium concentrations in plant parts greatly increased with increasing K supply. In faba bean, K concentrations in all shoot parts decreased with plant age irrespective of K supply while in chickpea K concentrations in leaves of K-deficient plants increased with plant age but those in stems decreased. For both species, young leaves had higher K concentrations than old tissues, especially in K-deficient plants. A greater proportion of leaf K was stored in the petioles when K supply was adequate than when K was deficient. Critical K concentrations were determined using the hand-fitted curve and Mitscherlich model at 90% maximum shoot weight and the 2-phase linear model. The critical concentrations varied between plant parts and among the methods used. Critical values decreased with leaf age and were higher in leaf petioles than in leaf blades. Critical K concentrations, developed from hand-fitted curves, in the 1st plus 2nd and 3rd plus 4th leaf blades of faba bean, and leaf petioles below the youngest fully expanded leaf (YFEL) of chickpea were similar between days 48 and 73 for faba bean and between days 55 and 80 for chickpea. It is recommended that the critical values for the diagnosis of K deficiency at 7–8-leaf stages are 1.3–1.5% in YFEL, 1.1–1.2% in the 1st plus 2nd leaf blades below the YFEL and 1.8–2.0% in whole shoot of faba bean, and 1.4–1.5% in YFEL, 2.7–2.8% in the 1st plus 2nd leaf petioles and 2.1–2.2% in whole shoot of chickpea. The gradient of K concentration between young and old leaves occurred before a decrease in shoot growth and may be used for the prognosis of K deficiency.

Ninety-two healthy Friesian cows were used to determine the concentration of calcium (Ca), zinc (Zn), magnesium (Mg), potassium (K) and sodium (Na) in bovine cervical mucus and to compare these concentrations in cervical mucus collected during spontaneous and induced oestrus. Cows were assigned to four groups: (1) no treatment (2) PRID for 12 days plus pregnant mare's serum gonadotrophin (PMSG; 1000 IU, i.m.) at the removal of the PRID (3) PGF2α , two doses (6 mg, i.m.) 11 days apart, and (4) PRID for 7 days plus one dose of PGF2α (6 mg, i.m.) 24 h before removal of the PRID. The cows of the three induced-oestrus groups received two artificial inseminations (AI), whereas those in the spontaneous-oestrus group received only one. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. The results of this study can be summarized as follows: (1) viscosity was significantly lower (P

The effect of potassium bicarbonate application to floodwater on the survival and growth of submergence-tolerant (FR13A) and -intolerant (IR42) rice cultivars during complete submergence was investigated. Potassium bicarbonate, applied at different rates to enhance floodwater carbon dioxide concentrations, increased the floodwater oxygen concentration. The treatment that had CuSO4, added alone to reduce algal growth showed the lowest O2 concentration at the time of submergence and after 10 d of submergence. Potassium bicarbonate at higher rates tended to maintain the floodwater pH near neutrality while copper sulfate affected pH increase during a 10-day period of complete submergence. Potassium bicarbonate addition led to 100% survival of tolerant FR13A. Potassium bicarbonate, even at 0.01 mol m–3 enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0 mol m–3, the survival was above 85%. Dry weights of submerged plants showed increases in both rice cultivars in floodwater treated with potassium bicarbonate. The dry weight and leaf chlorophyll concentration of both cultivars increased with increasing rates of potassium bicarbonate. Algal chlorophyll concentration of floodwater treated with potassium bicarbonate was comparable to that of the control without copper sulfate. The findings suggest a possibility of environmental manipulation of floodwater by potassium bicarbonate application to enhance the survival and growth of rice cultivars during complete submergence.

Pyrethrum (Tanacetum cinerariifolium), a small perennial plant, has been commercially grown for production of pyrethrins (Py) in Tasmania since 1983. Two field experiments were conducted on clay loam and sandy clay loam krasnozem soils at Harford and North Motton in the northern region and a two-year experiment on an alluvial sandy loam at Ouse in the southern region of Tasmania to study its potassium (K) requirements. Potassium, at rates up to 200 kg K ha-1, was band-placed at planting (basal K) of pyrethrum splits. At Ouse in the spring of the following year up to 100 kg K ha-1 was side-dressed in the subplots. No achene yield response was observed at Harford with the soil Colwell K (Kc) of 80 mg K kg-1 and North Motton (Kc = 132), but at Ouse (Kc = 50) in the first year a maximum increase of 86% in the achene yield was attained at 50 kg K ha-1. In the second year at Ouse, the achene yield response occurred with residual basal K up to the 200 kg ha-1 rate, where the achene yield was 3.9-fold greater than the control. In addition to the increase gained from the residual K in the second year, 50 kg side-dressed K ha-1 increased the achene yield by a maximum of 50%. Basal K did not have any effect on the Py concentration of the first year crops, but it increased the Py concentration in the second year crop at Ouse. Side-dressed K also increased the Py concentration. The Py yield at the highest rate of 200 kg basal and 25 kg side-dressed K ha-1 was more than 6.5-fold that in the control treatment. The Kc and the concentration of K in apical tissues were correlated to the rates of applied K, achene yield and Py yield, and their potential as techniques to predict pyrethrum response to K application is discussed.

The effects of nitrogen (N) and potassium (K) on leaf colour, vase life of flowering stems, and soil pH and electrical conductivity (conductance) were investigated for Australian waxflowers. Experiments were conducted on commercial plantings of Chamelaucium uncinatum cvv. Alba and Purple Pride, and a Chamelaucium hybrid (C. floriferum x C. uncinatum) known locally as Walpole wax, at 3 sites in South Australia. Nitrogen (as NH4NO3) and K (as K2SO4) were applied at rates up to 160 g N/plant and 80 g K/plant over several side dressings during the growing season. Application of N significantly (P0.05) at any site. For cv. Alba, application of N significantly increased vase life by 5 days in 1992 and 3 days in 1993. For Walpole wax, the effect of N was not consistent between years. Each year, the vase life of flowering stems from cv. Alba were consistently greater compared with stems from Walpole wax. Application of K did not significantly (P>0.05) effect vase life at any site. Annual applications of 80 or 160 g N/plant, as ammonium nitrate, significantly decreased soil pH by 0.3-1.4 units after 2-3 years, whereas application of K, as potassium sulfate, did not affect soil pH. The effect of applied N on soil conductance, although significant, was not consistent between sites. For example, at site 1, increasing the rate of applied N from 0 to 80 g N/plant increased conductance from 0.04 to 0.08 mS/cm in 1992. However, in 1993 it decreased from 0.04 to 0.02 mS/cm. The low conductance values (0.02-0.09 mS/cm) in the 0-60 cm soils, show that fertiliser salts did not accumulate over the course of the study to concentrations which adversely affect plant growth and yield. We conclude that N stress was a significant factor in the occurrence of poor leaf colour, and may be a major factor in the occurrence of defoliation during the flowering period. Optimising N nutrition improved leaf colour, vase life and, depending on the rate, did not significantly increase soil acidity or conductance after 2-3 years.

Native plants are increasingly being grown in Western Australia to produce flowers for export and the nutritional requirement of some of these species is not known. The nitrogen, phosphorus and potassium requirements for optimum growth of seedlings of one such species, Ptilotus exaltatus Nees., were measured in the glasshouse experiment reported here. There was a significant (P

Although soil salinity and potassium (K) deficiency are widespread in agricultural lands, there is a paucity of knowledge about the interactive effects of sodium (Na) and K on the growth and yield of major grain crops. In pot experiments, we examined salt tolerance of canola (Brassica napus L.), narrow-leafed lupin (Lupinus angustifolius L.) and wheat (Triticum aestivum L.), and crop K requirement under Na supply ranging from low to high. Plant growth and seed yield of all three crops were lower at 40 mg K/kg than at 100 mg K/kg soil. Although 100 mg Na/kg (4 dS/m in soil solution) had little effect on canola cv. Boomer and wheat cv. Wyalkatchem, the salt-treated narrow-leafed lupin cv. Mandelup died at 47 days after sowing, regardless of amount of soil K. In low-K soils, canola with 100 mg Na/kg and wheat with 50 mg Na/kg did not show K-deficiency symptoms and produced greater seed yield than plants with nil Na addition. At 100 mg K/kg, Na-induced reduction in growth and yield occurred only to plants with 200 mg Na/kg. However, at 160 mg K/kg, 200 mg Na/kg did not have an adverse effect. In canola and wheat, shoot K concentration increased and shoot Na concentration decreased with increasing amount of soil K; however, high soil K did not reduce shoot Na concentration in narrow-leafed lupin. The study showed that narrow-leafed lupin was very susceptible to salinity, whereas canola and wheat plants were relatively salt-tolerant. The stimulation of growth and yield in canola and wheat by low–moderate Na in low-K soils suggests partial K substitution by Na, and that adaptation of canola and wheat to salt-affected soils can be enhanced by high K supply.

Potassium diformate (KDF), as an acidifier, has been shown to improve growth performance in pigs, but it is not yet known whether KDF regulates gastric function. Thus, the objective of the present study was to investigate the effects of dietary KDF on gastric function in weaning piglets. One hundred and eighty Landrace × Large White piglets (bodyweight = 5.80 ± 0.15 kg) were weaned at 28 days old and randomly allocated into two groups, with six pens in each group and 15 piglets in each pen. Piglets in the control group were fed the basal diet, whereas the KDF-treated group was fed the basal diet supplemented with 10 g/kg KDF. After 35 days of feeding, the KDF treatment improved the bodyweight (P = 0.034) and reduced the relative weight of stomach (P = 0.050), decreased the hydrochloric acid concentration (P = 0.016) in the gastric digesta and the pepsin activity in the gastric oxyntic mucosa (P = 0.001) and increased the lactic acid concentration (P = 0.001) in the gastric digesta. Furthermore, KDF treatment increased the level of somatostatin (SS) (P = 0.009), but did not change the concentration of gastrin (P = 0.497) and the activity of H+-K+-ATPase (P = 0.575) in the gastric oxyntic mucosa. However, KDF treatment downregulated the expression of SS mRNA in the gastric oxyntic mucosa (P = 0.031) and upregulated the mRNA expression of gastrin (P < 0.001) and H+-K+-ATPase (P < 0.001) in the gastric oxyntic mucosa. These results suggest that the effects of KDF on weaning piglets may be related to the regulation of gastric function gene expression.

Six field experiments were conducted where Russet Burbank potatoes were grown with banded fertilizer consisting of diammonium phosphate (DAP) and either potassium sulfate (K2S04) or potassium chloride (KCl). At each site, rates of nitrogen (N), phosphorus (P) and potassium (K) were matched as closely as possible for each K fertilizer treatment. At four of the six sites, potatoes grown with K2S04 had tuber and petiole cadmium (Cd) concentrations 20-30% lower than did potatoes grown with KCl. The use of K2S04 instead of KCl appears to offer considerable promise as a means of decreasing tuber Cd uptake. Sulfate ions presumably promote increased soil adsorption of soil and/or fertilizer Cd compared with chloride ions, and so decrease Cd availability. We attributed the lack of difference in tuber and petiole Cd between K sources at two sites to either leaching, chloride in irrigation water, or at one site to a higher than desired rate of NPK fertilizer with the sulfate treatment. Any one of these may have offset decreases in Cd uptake due to the presence of sulfate ions.

When a high-affinity K + transporter, HKT1, was cloned from the roots of K + -starved wheat and characterized, it seemed that the wheat high-affinity K + -uptake mechanism had been found. We review the present status of HKT1 as a putative component of the wheat root high-affinity mechanism, concluding that its role remains unclear, as it also does in barley. We describe a new attempt to find its role. High-affinity K + transport in K + -starved wheat seedling roots was studied by measuring K + -evoked depolarization. A single dominant transport system was shown to carry K + , Rb + and Cs + , with a binding site selectivity of about 1:1:0.15, respectively. We showed that the small effect of 1 mM Na + on K + -evoked depolarization could be inhibition under some conditions and stimulation under others. We confirmed that the effect of 1 mM Na + was to raise the K + affinity and to reduce transport velocity. In 0 Na + , high pH greatly reduced the K + -affinity, but in 1 mM Na + , high pH had no effect. So, in a given test, the effect of Na + was to increase or decrease K + -evoked depolarization, depending on the test [K + &rsqb; and the pH. We discuss simplified, but plausible, kinetic models for this interaction of pH and Na + . The simplest model includes a K + symporter driven by H + or Na + depending on their relative concentrations and affinities, with random binding order for the two possible driver ions. This symporter would differ from HKT1 in its selectivity for Rb + vs K + and in its inability to carry Na + alone. No role has been found for a symporter resembling HKT1 as it is presently characterized by heterologous expression.

Sodium is a beneficial mineral for some plant species when external concentrations are low. The role of Na+ in energising K+ acquisition in terrestrial plants has recently been suggested because of evidence demonstrating that wheat root cells express a high-affinity Na+-energised K+ symporter. To determine whether low concentrations of Na+ improve the K+ nutrition and growth of wheat, long-term growth and short-term tracer flux experiments were conducted. Long-term growth experiments were conducted over a range of K+ concentrations, at acidic and alkaline pH, with and without 500 µM NaCl. Plant biomass and tissue Na+ and K+ content was measured. Short-term experi-ments were conducted using tracers to determine whether low concentrations of Na+ or K+ stimulate Rb+ or Na+ uptake, respectively. Sodium stimulated the growth of wheat only at low (20 µM) external K+ in one of the long-term experiments, but not in two other experiments. Na+ did not stimulate Rb+ uptake, but K+ stimulated Na+ uptake in short-term tracer flux experiments. The results suggest that low concentrations of Na+ do not increase K+ uptake to a large extent, and only when light levels are low does Na+ have a beneficial effect on the growth of wheat.

Summary. Native plants are increasingly grown in Western Australia to produce flowers for export. The nitrogen (N), phosphorus (P) and potassium (K) requirements for optimum production of one of these species, Geleznowia verrucosa (Yellow Bells), was measured for 17-week-old seedlings in a glasshouse experiment reported here. There was a significant (P

Five field experiments were conducted over 3 years in the Mt Lofty Ranges (4 sites) and the Upper South East (1 site) to examine the significance of main effects and interactions between nitrogen (N, up to 360 kg N/ha), phosphorus (P, up to 320 kg P/ha), and potassium (K, up to 480 kg K/ha) on total yield, yield of 80-350 g size grade, specific gravity, crisp colour, and chemical composition of tubers of potato cv. Kennebec. There were significant (P

Data are presented from 3 field experiments that studied the effects of nitrogen (N) up to 360 kg N/ha, phosphorus (P) up to 100 kg P/ha, and potassium (K) up to 480 kg K/ha on tuber yield and the concentration of N, P, and K in petioles of youngest fully expanded leaves (P-YFEL) of potato cvv. Kennebec and Atlantic sampled when the length of the longest tubers was 10-15 mm. Data on the significance of relationships between total N and P, total N and nitrate-N, and chloride and nitrate-N in P-YFEL are also presented. At 1 site, Atlantic yielded 18% higher than Kennebec; at another, it yielded 21% less. Significant K x cv. and N x cv. interactions occurred at some sites. Increasing rates of applied N significantly increased total N concentrations in P-YFEL at all sites and nitrate-N concentrations at sites that were N-deficient. At 1 site, increasing the rate of applied P from nil to 100 kg P/ha significantly increased total N concentration from 2.8 to 3.4%. Total N concentrations in P-YFEL of Atlantic were significantly lower than Kennebec. For total N, there were significant N x K and P x cv. interactions. There was no significant interaction between N, P, and K in their effects on nitrate-N concentration in P-YFEL. At all sites, the application of N and P significantly increased P concentrations in P-YFEL, and mean concentrations were significantly greater in Kennebec than Atlantic. At sites deficient in K, the application of K significantly decreased P concentration. Significant N x cv. and P x cv. interactions occurred at 2 sites. At both K-deficient and non-responsive sites, increasing rates of applied K significantly increased K concentrations in P-YFEL. Differences between cultivars in K concentration were not significant at 2 sites, and although significant at the third, the difference (0.2%) was of little practical importance. At 2 sites, significant N x K and K x P interactions were found. Significant positive linear relationships were found between total N and P concentrations in P-YFEL for both the experimental sites (r = 0.46-0.84) and commercial crops (r = 0.43-0.61). Except at site 1 (r = 0.85), total N and nitrate-N concentrations were not highly correlated. For 1 experimental site and for all the growing regions, there were significant negative linear relationships between nitrate-N and chloride concentrations in P-YFEL (r = -0.38 to -0.83). We suggest that the synergism between total N and P and the negative correlation between nitrate N and chloride are important factors to be considered to ensure reliable interpretation of early-season, petiole plant test data for these nutrients in potato crops; that the critical P and total N concentrations are different for Kennebec and Atlantic; and that when K is not yield-limiting, the main effects and interactions between K and total N, P, or nitrate-N do not confound the use of these nutrients in P-YFEL to assess the P, N, or K status of potato crops.

Potassium (K), calcium (Ca) and magnesium (Mg) are three macro-elements essential for plants and animals. The ratios K : Mg or K : (Ca + Mg) are viewed as indices of physiological status in livestock animals. In plants, Ca, Mg and K concentrations can vary with climate in terrestrial ecosystems. Here, with a widespread tree species (Chinese cork oak, Quercus variabilis Blume) and an acorn predator (the weevil Curculio davidi Fairmaire), we investigate how K, Ca and Mg vary in soils, plant tissues (leaves and acorns) and a consumer (herbivore insects) with climatic variables induced by latitude (LAT) across the temperate–subtropical areas of eastern China. Concentrations of K, Ca and Mg in soils, leaves, acorns and weevil larvae showed different degrees of variation across the study area, but only Mg concentration increased significantly with rising LAT across all four trophic levels, albeit with varying slopes. With rising mean annual temperature (MAT) and precipitation (MAP), soil Ca significantly decreased, as did leaf and acorn K concentrations, whereas all four tropic levels showed significant decreases in Mg content with both MAT and MAP (P

The effects of nitrogen (N) and potassium (K) on coffee (Coffea arabica L.) growth and yield in a shallow sandy soil in North Queensland were studied over 5 years following field establishment. High rates of N (416 and 624 kg/ha) applied frequently were necessary for rapid growth and yield of cvv. Kairi Typica (K2), Caturra Rojo (CR33), Catuai Rojo (CR35), and Bourbon Red (B61). Although data were not significant, mean yields with 416 and 624 kg N/ha were greater than with 208 kg/ha by 124 and 145% in 1986, by 12 and 26% in 1987, and by 38 and 31% in 1988. Increasing rates of K (63, 126 and 189 kg K/ha) did not affect growth and did not significantly increase yield in the later stages of the experiment. Neither N nor K had any affect on green bean size or time of berry maturity. CR35 was the highest yielding cultivar (3752 kg/ha of green bean in 4 years of cropping) and B61 the lowest (2067 kg/ha). Height and girth were ranked K2 > CR35 > CR33 > B61. B61 also had significantly fewer and shorter longest primary laterals. CR35 ripened later than other cultivars, while B61 produced the highest percentage of large beans, and K2 the highest percentage of small beans. Preliminary recommendations for coffee growers in this region are 100 kg N/ha in year 1, increasing to 400 kg/ha in year 4; and 80 kg K/ha in year 1, increasing to 320 kg K/ha in year 4. Monthly, rather than quarterly, applications are recommended.

The effects of 3 nutrient solution formulations on the production and quality of the Sim carnation varieties, Raggio d'Sole, White Sim, Manon and Doria grown in rockwool substrate were evaluated over 12 months in northern New South Wales. The solutions were: a standard (Std) formulation with a K:N ratio of 1.29:1.00, approximating that in mature carnations with N supplied as NO3-; the standard solution with 10% of the N as NH4+ (Std + NH4+); and a formulation with increased Ca and reduced K (High Ca). Production peaks occurred in March and October when the substrate was sampled for leachate nutrient composition and the flowers were assessed for quality. Total flower production from the Std + NH4+ (9.9/plant) and High Ca (9.7/plant) treatments exceeded (P0.05) (mean of 10.3/plant) from August to December. Over February-December, production from the Std + NH4+ treatment (20.8/plant) exceeded (P0.05) by nutrient solution formulation. Stem diameter, stem strength and vase life were unaffected by nutrient formulation while flowers produced in March had thinner (3.11 v. 5.24 mm diameter) and weaker (139 v. 42 mm deflection from horizontal) stems than those produced in October. The pH in rockwool slabs was stable over time and compared to the standard treatment (7.17), it was lower (P

Fruit yield, leaf nutrient concentrations and growth response of young Valencia orange trees to 4 rates of nitrogen (N, 75-450 kg/ha), phosphorus (P, 0-180 kg/ha) and potassium (K, 0-360 kg/ha) were studied using 2 soil management systems (sod-sown and bare ground) and 2 rootstocks (Troyer Citrange and Sweet Orange). Eight-year-old Sweet Orange produced maximum yield at the higher rates of applied N and P and medium level of K, but at 12 years of age, highest yields occurred at the lowest rate of applied N, medium P and nil K. High N without P at year 12 strongly depressed yield especially on bare soil. Phosphorus application at high rates of N greatly increased yield but had no effect at lower rates of N. The effect of nutrients on yield was smaller on Troyer than on Sweet Orange rootstock. Leaf N concentration increased with amount of N applied and slightly increased with K applications but not with applied P. Leaf P concentrations increased with higher rates of applied P, especially in year 12 and at the lowest rate of applied N. Both rootstock and management affected leaf P concentration. Leaf K increased with amount of applied K. Highest concentrations of leaf K were from Troyer trees under bare soil management but this trend declined with time. The effects of fertilisers on tree size were small and varied with rootstock and management.

Efficient and effective nutrient management decisions are critical to profitable and sustainable milk production on modern Australian dairy farms. Whole-farm nutrient balances are commonly used as nutrient management tools and also for regulatory assessment on dairy farms internationally, but are rarely used in Australia. In this study, nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) imports and exports were measured during a standardised production year on 41 contrasting Australian dairy farms, representing a broad range of geographic locations, milk production, herd and farm size, reliance on irrigation, and soil types. The quantity of nutrients imported varied markedly – with feed and fertiliser generally the most substantial imports – and were principally determined by stocking rate and type of imported feed. Milk exports were the largest source of nutrient exports. Nitrogen balance ranged from 47 to 601 kg N/ha.year. Nitrogen-use efficiency ranged from 14 to 50%, with a median value of 26%. Phosphorus balance ranged from –7 to 133 kg P/ha.year, with a median value of 28 kg P/ha. Phosphorus-use efficiencies ranged from 6 to 158%, with a median value of 35%. Potassium balances ranged from 13 to 452 kg K/ha, with a median value of 74 kg K/ha; K-use efficiency ranged from 9 to 48%, with a median value of 20%. Sulfur balances ranged from –1 to 184 kg S/ha, with a median value of 27 kg S/ha; S-use efficiency ranged from 6 to 110%, with a median value of 21%. Nitrogen, P, K and S balances were all positively correlated (P < 0.001) with stocking rate and milk production per ha. Poor relationship between P, K and S fertiliser inputs and milk production from home-grown pasture reflected the already high soil fertility levels measured on many of these farms. The results from this study demonstrate that increasing milk production per ha will be associated with greater nutrient surpluses at the farm scale, with the potential for greater environmental impacts. We suggest that simplified and standardised nutrient balance methodologies should be used on dairy farms in Australia to help identify opportunities for improvements in nutrient management decisions and to develop appropriate industry benchmarks and targets.

The potassium (K) status of 5 major soil types, under sugar beet cultivation for 35–40 years, and adjoining virgin lands were compared. Fifty-nine paired surface soil samples belonging to 24 soil series from the major sugar beet growing areas in Western Azarbaijan province located in the north-west of Iran were studied to ascertain whether relative K form sizes and K adsorption behaviour of the soils are being changed by long-term cropping. The samples were analysed for soil physical and chemical properties, mineralogy of clay fraction, different forms of K, and K adsorption characteristics. The soils are alkaline and calcareous. The K-bearing mineral illite is the dominant clay mineral in Typic calcixerepts, Typic haploxerepts, and Typic endoaquepts, whereas in Vertic calcixerepts and Vertic endoquepts, the clay mineralogy is dominated by smectite. A highly significant relationship (r2 = 77, P ≤ 0.001) was observed between CEC and smectite content. No changes in K-bearing minerals were detected due to cropping and K depletion. Soil solution K (So-K) constituted 1.7% of exchangeable K (Ex-K) and 1.4% of non-exchangeable K (NEx-K) for the cultivated soils and 1.8% of Ex-K and 2% of NEx-K for the adjacent virgin land. A pronounced significant decline (P ≤ 0.001) in the Ex-K content from 507 to 270 mg/kg (a drop of 45%) and a less significant degree (P ≤ 0.05) in the So-K content from 28 to 12 mg/L (a drop of 55%) were detected in the soil series of Typic calcixerepts as a result of long-term cropping. Continuous sugar beet cropping did not result in changes in the NEx-K contents in any soils except in Vertic endoaquepts containing low illite. A highly significant positive relationship (r2 = 0.79, P ≤ 0.001) was observed between values of NEx-K and illite contents, indicating that this form of K is mainly released from the frayed edges of illite. Paired t-test revealed that continuous sugar beet cultivation increased significantly (P ≤ 0.01) K adsorption in Typic calcixerepts, Typic haploxerepts, and Vertic endoaquepts, where exchangeable K was decreased as a result of intensive cultivation.

Cystic ovarian follicle (COF) is one of the most frequently diagnosed ovarian diseases and a major cause of reproductive failure in cattle. Despite an abundance of reports on this subject, the exact pathogenesis of COF still remains unclear. It is generally accepted that disruption of the hypothalmo-pituitary-gonadal axis, by endogenous and/or exogenous factors, causes cystic formation. We here examined whether ion concentration and expression of ion channels are altered in the follicle fluid derived from a Korean native cow with COF. In an ovary with a cystic follicle, granulosa cell layers were exfoliated; the theca interna was thinner than that in an ovary without cystic follicle, based on histological examination. Concentrations of K+, Na+, and Cl- in COF fluid (COFF) were 10.4 � 3.5 mM, 138 � 12 mM, and 104.9 � 7.0 mM, respectively. In COFF, K+ concentration showed a significant difference from the value observed in normal follicle fluid (NFF) (P < 0.05; NFF: 10.4 � 3.5 mM vs. COFF: 6.2 � 0.8 mM). The total numbers of follicles observed (normal, 3–5 mm in diameter vs. COF, 20–30 mm in diameter) were 200 and 20 in normal and COF, respectively. To compare mRNA expression of K+ channels, we performed semiquantitative RT-PCR using follicle fluid and ovaries with or without cystic follicles. RT-PCR showed that mRNA levels of TASK channels (TASK-1, TASK-3, and TASK-5) decreased by 50% in COFF and an ovary with cystic follicles compared to NFF and a normal ovary. TASK channels are involved in apoptosis of mammalian cells. Our results suggest that potassium may play an important role in the pathogenesis of COF.

The Better Fertiliser Decision for Crops (BFDC) National Database holds historic data for 356 potassium (K) fertiliser rate experiments (431 treatment series) for different rain-fed grain crops and soil types across Australia. Bicarbonate-extractable K (Colwell soil-test K) is the most extensively used soil test reported in the database. Data are available for several crop species grown on a range of soil types from all states except Tasmania. Species represented and number of treatment series in the database are: wheat (Triticum aestivum L.), 254; barley (Hordeum vulgare L.), 5; canola (Brassica napus L.), 130; lupin (Lupinus angustifolius L.), 32; sunflower (Helianthus annuus L.), 10; sorghum (Sorghum bicolor L.), 5; and faba bean (Vicia faba L.), 2. About 77% of the available soil-test K (STK) data on wheat, canola, and lupin are from Western Australia. The usual sampling depth of 0–10 cm is recorded for all treatment series within the database, while 68% of experiments have STK information from other soil horizons down the profile, usually in 10-cm increments. The BFDC Interrogator, a comprehensive data search and calibration support tool developed for use with the BFDC National Database, was used to examine STK–yield relationships for each crop across Australia, with more detailed analysis by state/region and then by soil type if data were available. The BFDC Interrogator was used to determine a critical STK concentration to achieve 90% of the maximum relative yield (90%RY) for each crop species, with a critical range (determined by the 70% confidence limit for the 90%RY) also reported. The STK for 90%RY for wheat was 40–41 mg/kg on Tenosols and Chromosols, ~49 mg/kg on Kandosols, and ~64 mg/kg on Brown Ferrosols. There was some evidence of critical values increasing with increasing crop yield and on soils with no acidity constraints to root growth, with effects presumably driven by increased crop K demand. The STK for 90%RY for canola, grown mainly on Tenosols, was similar to that for wheat, ranging from 43 to 46 mg K/kg, but for lupin, also grown mainly on Tenosols, the STK for 90%RY was a relatively low ~25 mg K/kg. Data for sunflower were limited and the STK for 90%RY was poorly defined. A comparison of critical STK concentrations for different crops grown on Tenosols suggested that critical ranges for 90%RY of lupin (22–27 mg K/kg) were significantly lower than that for wheat (32–52 mg K/kg) and canola (44–49 mg K/kg). Critical STK values were not determined for sorghum and faba bean.

Potassium (K) is the principal mineral solute contributing to osmotic adjustment (OA) in many crop species, and the magnitude of OA under drought stress may be increased by application of K fertilisers. Genotypic differences in either the capacity for OA under drought stress or the efficiency of K uptake and utilisation by wheat have been separately documented. However, it is not known whether genotypic differences in K uptake and utilisation are linked to differences in OA under drought stress. In this study, we quantified changes in OA in response to variable K fertilisation among five wheat genotypes with contrasting efficiency of K uptake and utilisation. Fertilisation with K increased OA for most genotypes by increasing K+ uptake and translocation into shoots and its subsequent accumulation in young leaves when drought stress was imposed. Accumulation of K+ in young leaves accounted for 36–51% of OA among the genotypes. The magnitude of OA achieved by genotypes under K fertilisation was highly correlated with the net content of K accumulated in shoots. With K fertilisation, differences in shoot K+ content accounted for 84% of the difference in OA among wheat genotypes. By comparison, for plants without K fertilisation, K+ accumulation in young leaves contributed only 17–28% of OA. At low K supply, the magnitude of OA achieved by genotypes was independent of the content or concentration of K+ in shoots. Under K-fertilised conditions, genotype Nyabing achieved the highest OA under drought stress, accumulated the highest concentration of K+ in young leaves (–0.87 MPa, accounting for 51% of OA), and had the greatest net K+ content in shoots. Genotype Wyalkatchem accumulated the smallest content of K+ in shoots and the lowest K+ concentration in young leaves (–0.40 MPa, accounting for 38% of OA), and achieved the lowest OA under drought stress. The greatest OA was achieved where high genotypic capacity to take up K was paired with conditions of high soil K availability.

Most sandy soils used for cropping in south-western Australia (SWA) have now become potassium (K) deficient due to removal of K in hay and grain, so it is now profitable to apply K fertiliser to most barley (Hordeum vulgare L.) crops in the region. Leaf diseases of barley crops in the region have increased in recent years particularly in the in medium to high (350–600 mm annual average rainfall) areas of SWA. Seventeen field experiments were undertaken to determine the effect of applications of K fertiliser, either the chloride (KCl) or sulfate source (K2SO4), on grain yield increases and on the percentage leaf area diseased (%LAD) when diseases were controlled or not controlled by fungicide sprays. Maximum grain yield of barley was achieved where adequate K fertiliser (~8–22 kg K/ha) was applied and leaf diseases were controlled by fungicide. Applying increasing amounts of applied K fertiliser (0–120 kg K/ha) to barley decreased the %LAD by powdery mildew (Blumeria graminis f. sp. hordei Syn.) and spot-type net blotch (Pyrenophora teres f. maculata (Sacc.) Shoem.) and increased grain yield. By contrast, when leaf rust (Puccinia hordei G. Otth) was present the %LAD was unaffected by K application. When powdery mildew was the major disease, larger increases in grain yields and larger reductions in %LAD were obtained when KCl was used instead of K2SO4. About twice as much K fertiliser as K2SO4 was required for 90% maximum grain yield compared with KCl where powdery mildew was present. Applying larger amounts (>40 kg K/ha) of K fertiliser than required to achieve maximum grain yields did not further reduce %LAD by powdery mildew. There were no significant differences between the 2 sources of K fertiliser on the %LAD by spot-type net blotch. Generally, the percentage protein content and hectolitre weight of grain were unaffected by K fertiliser. Potassium fertiliser decreased the percentage grain < 2.5 mm (known locally as screenings) and control of the foliar leaf diseases by applications of fungicide resulted in a decrease in protein content and screenings and increased hectolitre weight of barley grain. The concentration of K in dried shoots that was related to 90% of the maximum shoot yield (critical diagnostic K) decreased as the plant matured, and was ~41 g/kg at Z22, ~30 g/kg at Z32, ~20 g/kg at Z40, and ~15 g/kg at Z59. The concentration of K in dried shoots which was related to 90% of the grain yield (critical prognostic K) decreased as plant matured, and was similar to critical diagnostic K values. Leaf disease had little effect on critical concentrations of K at early growth stages (Z22 and Z32).

The objective of the study was to compare the effect of 2 free serum chemically defined media, synthetic oviduct fluid medium (SOF) and optimized simple potassium medium (KSOM) on embryo development of in vitro-produced embryos. Bovine ovaries were collected from a local abattoir. Cumulus oocyte complexes (COC) were obtained by follicular aspiration of 3- to 6-mm follicles and in vitro-matured in TCM-199 for 24 h at 39°C, 5% CO2, and high humidity. After IVM, COC were co-incubated with sperm at a concentration of 1.5 × 106 spermatozoa per mL in TALP medium for 18 h at 39°C, 5% CO2, and high humidity. Presumptive zygotes were randomly assigned to SOF (n = 312) or KSOM (n = 290) media, both supplemented with essential and nonessential amino acids plus 0.6% BSA. Zygotes were cultured at 39°C, 5% CO2, 5% O2, 90% N2, and high humidity for 9 days. Cleavage rate was evaluated on Day 2 (Day 0 = day of insemination) and the number of blastocysts and hatched blastocysts were recorded on Days 8 and 9. Expanded blastocysts from Day 8 (n = 45/per culture medium) were fixed and stained with bisbenzimide (Hoechst 33242), and the total number of embryonic nuclei was counted by fluorescence microscopy (Optiphot, Nikon, Tokyo, Japan). The study was conducted in 6 replicates for embryo development assessment and 3 replicates for embryonic nuclei counting. Data were analyzed using Fisher’s exact test and Student’s t-test. The percentage of presumptive zygotes to develop into 2 to 4 cells (22.4 v. 24.2%) or > 4 cells (47.7 v. 53.4%) did not differ (P > 0.05) between SOF and KSOM on Day 2, but total embryo cleavage ≥ 2 cells was greater (P < 0.05) in KSOM (76.8%) than in SOF (68.5%). However, the percentage of blastocysts developed on Day 8 and 9 was greater (P < 0.05) for zygotes cultured in SOF (22.1 and 25.6%) than for those cultured in KSOM (15.1 and 18.9%). Furthermore, the percentages of hatched blastocysts on Day 8 and 9 were also greater (P < 0.05) for zygotes cultured in SOF (18.8 and 36.2%) than for those cultured in KSOM (4.7 and 12.5%). In addition, expanded blastocysts developed in SOF had higher total mean number of embryonic nuclei than those developed in KSOM (P < 0.05; 128.8 ± 7.5 v. 84.3 ± 8.9, respectively). In conclusion, the use of SOF resulted in significantly greater percentage of blastocysts and hatched blastocysts compared with KSOM. Additionally, expanded blastocysts developed in SOF displayed a higher number of cells. This study was supported by Convenio Desempeño en Investigacion (2007-DGI-CDA-04), Universidad Catolica de Temuco and DiD-UAcH: S-2009-26.

Poor phosphorus (P) and potassium (K) nutrition limits the growth and yield of many cotton (Gossypium hirsutum L.) crops in Australia. The demand for nutrients from cotton crops has risen as yields have increased over the past 40 years, and some soils have become depleted in these nutrients. Cotton is commonly grown on sodic soils that are more prone to nutritional problems. A survey of thirty-one sites over four years in northern NSW, Australia included twelve sites that had sodic topsoil. However, available soil P and K at all sites were above established critical values for cotton crops. Soil sodicity was negatively correlated with available soil P and K, and positively with soil salinity and chloride. Cotton leaf P and K concentrations at flowering were negatively correlated with leaf sodium (Na) concentration. The cotton crops growing in sodic soils produced 20% less dry matter (3 weeks before crop defoliation) and crop P and K uptake was reduced by 23% and 25%, respectively, whereas Na uptake was 107% higher. High soil sodicity also reduced the uptake of micro-nutrients. Two field experiments in adjacent sodic and non-sodic areas on one farm showed a yield response to P fertiliser application at the non-sodic site only, but where soil P availability was above the accepted critical value. Application of K fertiliser did not increase crop K uptake or yield. The lower yield and poorer growth of irrigated cotton on sodic soils was related to higher Na uptake and lower P and K uptake, possibly due to restricted root growth in sodic soils.

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 subterraneum L.) and annual and Italian ryegrass (Lolium rigidum Gaud. and L. multiflorum Lam.). 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.

Most sandy soils used for cropping in south-western Australia are now deficient in potassium (K) due to removal of K from soil in hay and grain, and profitable grain yield responses to applied fertiliser K are commonly obtained for spring wheat (Triticum aestivum L.) and canola (oilseed rape, Brassica napus L.). However, there are only limited data comparing the K requirements of these 2 species in the region. In a glasshouse experiment we compared the K requirements of wheat (cv. Westonia), conventional canola cv. Outback (cultivars of canola not produced by classical breeding techniques to be tolerant of specific herbicides), triazine-tolerant (TT) canola cvv. Pinnacle and Surpass 501, and imidazolinone-tolerant (IT) canola cv. Surpass 603. The following measures were used: yield of 54-day-old dried shoots and seed (grain) without added K, applied K required to produce 90% of the maximum yield of shoots and grain, K required to attain a K concentration in shoots of 30 g/kg, and K required to achieve a K content in shoots (K concentration multiplied by yield) of 40 mg/pot. We also determined for each species and cultivar the concentration of K in dried shoots that was related to 90% of the maximum grain yield, to estimate critical concentration in shoots below which K deficiency was likely to reduce grain production. All 4 canola cultivars produced similar results. Both canola and wheat produced negligible shoot yields and no grain when no K was applied. For each species and cultivar the amount of applied K required to produce 90% of the maximum yield was similar for shoots and grain, and was ~121 mg K/pot for the 4 canola cultivars and 102 mg K/pot for wheat, so ~19% more K was required for canola than for wheat. For each amount of K applied, the concentration of K in shoots was greater for canola than for wheat. The amount of applied K required to attain a K concentration of 30 g K/kg in shoots was ~96 mg K/pot for canola and 142 mg K/pot for wheat, so ~48% more K was required by wheat than by canola. The amount of K applied required to achieve a K content of 40 mg K/pot in shoots was ~46 mg K/pot for canola and 53 mg K/pot for wheat, so ~13% more applied K was required by wheat than by canola. The data suggest that canola roots were better able to obtain K from soil than wheat roots, but wheat used the K taken up more effectively than canola to produce shoots and grain. The concentration of K in dried shoots of 54-day-old plants that was related to 90% of the maximum dried shoot yield or grain was ~32 g/kg for canola and ~23 g/kg for wheat.

Drought stress is an important limitation to the growth and grain yield of pearl millet in arid and semi-arid regions of the world. Potassium iodide, a senescing agent, was used as a screening tool for evaluating drought tolerance of 22 strains of pearl millet at the grain development stage (grain filling) under glasshouse conditions. In order to use potassium iodide as a selection method in breeding programs for improvement of drought tolerance, the technique was compared with some drought evaluating parameters such as water retention capability, osmotic adjustment, photosynthetic capacity and water-use efficiency. Application of a 0.3% solution of potassium iodide at anthesis was very effective in causing drought stress, and hence grain yield reduction, in pearl millet. It showed a significant association with water deficit in growth attributes such as fresh and dry weights of shoots, and grain yield. Osmotic adjustment, water retention capability (decrease in weight of excised leaves during 5-h drying period), photosynthetic rate, and single-leaf water-use efficiency (net CO2 assimilation rate/transpiration) did not show positive relationships with the degree of drought tolerance measured using potassium iodide spray or water-deficit treatment. A large amount of variation in drought tolerance observed in 22 lines of pearl millet can be of considerable practical value. For example, the 3 lines ICMP-83720, ICMV-9413 and ICMV-94472, ranked as highly drought tolerant on the basis of their overall growth and physiological performance, and could be of direct use under mild drought conditions.

An efficient screening procedure is essential for breeding for salinity-tolerant crops, but there is no consensus regarding the best approach. While some authors argue that the selection of tolerant genotypes should be undertaken under field conditions, others believe that field-based trials for salinity tolerance is problematic due to confounding environmental factors. Also, the choice of specific physiological trait(s) used is often subjective, frequently depending on the ‘personal philosophy’ of the researcher. In this work, we undertook an unbiased assessment of a multitude of physiological and agronomical parameters in an attempt to find a combination that would satisfy two main criteria: (1) be relatively easy and quick to measure; and (2) possess a high predictive power. Fourteen physiological and agronomical traits were measured and analysed using various statistical methods (multiple regression, cluster analysis, principal component analysis). Our results indicate that measuring just two parameters; changes in the chlorophyll content in the 5th leaf after 6 weeks of NaCl treatment, and shoot sap K+ content in control plants, measured at the same time, satisfied these requirements and could be used as efficient screening tools in wheat breeding programs. Interestingly, salt tolerance was associated with lower but not higher K+ content in control plants. The physiological mechanisms involved are discussed.

The predominantly sandy soils of south-western Australia have become potassium (K) deficient for spring wheat (Triticum aestivum L.) production due to the removal of K from soil in grain and hay. The K requirements of canola (rape, Brassica napus L.) grown in rotation with wheat on these soils are not known and were determined in the study reported here. Seed (grain) yield increases (responses) of canola to applications of fertiliser K occurred at sites where Colwell soil test K values (top 10 cm of soil) were

Potassium (K) deficiency is now common in sandy soils of south-western Australia and the K requirements of most pasture species grown in rotation with crops in the region are not known. In a glasshouse experiment using a K deficient yellow sand, we compared the K requirements of 5 pasture species now commonly grown in the region: French serradella (Ornithopus sativus Brot.) cv. Cadiz, yellow serradella (Ornithopus compressus Brot.) cv. Santorini, balansa clover [Trifolium balansae, classified as T. michelianum Savi var. balansae (Boiss)] cv. Paradana, 2 subterranean clover (Trifolium subterraneum L.) cultivars, cv. Seaton Park (subspecies subterraneum) and cv. Trikkala (subspecies yanninicum), and annual ryegrass (Lolium rigidum Gaud) cv. Wimmera. After 56 days of growth, above-ground growth was harvested and analysed for total K. Mitscherlich curves were fitted to yield of dried shoots, K concentration and K content (K concentration multiplied by yield) of the shoots. These fitted curves were used to determine the amount of K required to produce 75% of the maximum yield of dried shoots, K required to attain a K concentration in dried shoots of 25 g/kg, and K required to achieve a K content in dried shoots of 250 mg K/pot. Annual ryegrass and yellow serradella more effectively used indigenous soil K and applied K to produce dried shoots than the other species and cultivars, with the other species and cultivars requiring about 55% more applied K to produce 75% of the maximum shoot yield. The K content in dried shoots estimated the total K taken up from the soil, and annual ryegrass took up least K from soil, but it required least applied K to produce 75% of the maximum shoot yield, indicating it used the K it took up very effectively to produce shoots. Yellow serradella took up most K and, after annual ryegrass, it needed least applied K to produce the target yield of dried shoots. After yellow serradella, subterranean clover cv. Trikkala took up most K from soil, but it required nearly the most applied K to produce the target shoot yield so it was inefficient at using K taken up to produce the shoots. For all the other species and cultivars, K requirement was similar as assessed by yield or K content data. The critical concentration of K required for 90% maximum yield of dried shoots was about (g K/kg) 24 for balansa clover, 23 for both subterranean clover cultivars, 21 for yellow and French serradella, and 15 for annual ryegrass.

Relationships between amounts of superphosphate applied to pasture and stocking rate on available nutrient status were assessed from 1979 to 2000 on a chromosol derived from basalt at Hamilton, Victoria. The pastures were stocked with sheep at low, medium, or high grazing pressures in factorial combination with 6 levels of superphosphate. Overall annual amounts of single superphosphate (8.8% P, 11% S, 19% Ca) applied ranged from 0.4 to 36 kg P/ha. Potassium chloride (KCl) was applied to all plots periodically. Average stocking rates ranged from 7 to 19 dry sheep equivalents (DSE)/ha. The nutrient status of plots was monitored by sampling the soil to a depth of 10 cm, avoiding the areas used by the sheep for camping. In 1994, samples of topsoil (0–5 cm and 5–10 cm) were taken from the camp areas and non-camp areas in each plot in order to assess 'plant-available' P, S, and extractable cations. Changes in P and S with depth to 80 cm in high and low grazing pressure treatments were also assessed. The influence of cumulative P applied on Olsen P varied with time and grazing pressure. During the first 12–15 years, the Olsen P of high grazing pressure plots was greater than that of low grazing pressure plots, but subsequently the reverse has been the case. Plant-available S also increased where more superphosphate had been applied. Levels were greater than 7 mg S/kg soil except at the lowest level of superphosphate, indicating that forms of P fertiliser with less S could be used here. After initial applications of KCl, this fertiliser was not applied for 8 years. During this time the K status fell from 270 to 120 mg K/kg soil, just above where plant responses to K are likely, emphasising the need to monitor the K status of productive pastures on these soils. Levels of exchangeable Mg2+ fell as more superphosphate was used, whereas levels of Ca2+ rose. The Olsen P of soil deeper than 10 cm was always less than 5 mg P/kg soil. P supply to deep-rooted pasture plants may thus be limiting when the topsoil is dry. These results, together with published assessments of animal production at this site, show that for pastures fertilised annually, the Olsen P associated with the most profit varied from 7 mg P/kg soil at 7 ewes/ha (10.5 DSE/ha), to 14 mg P/kg soil at 18 ewes/ha.