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It is well documented that sole application of potassium (K) or mycorrhizal fungi can alleviate heavy metal stress in plants. As an indicator of the efficient defense in the mycorrhizal fungi-plant system, glomalin synthesis in the rhizosphere can be determined. In this study, interactive effects of mycorrhizal fungi (MY) and K on glomalin content, heavy metal uptake and mycorrhizal properties of sunflower plants were examined with three soil K levels (0, 100, and 200 mg K kg−1 using K2SO4). The three levels of mycorrhization are: i) no mycorrhizal inoculation, ii) Rhizophagus irregularis inoculation, and iii) mixed mycorrhizal inoculum application. Joint application of potassium and mycorrhiza significantly increased the percentage of root colonization and easily extractable glomalin (EEG), showing 56% root colonization in the treatment of K100 + mixed mycorrhiza and 178 µg EEG g−1 in the treatment of K200 + mixed mycorrhiza. Joint application of MY and K significantly reduced the translocation of heavy metals to the shoot of the plants. The highest total uptake of Zn by plants per pot (2.01 mg pot −1) and Pb (0.78 mg pot −1) were found in non-mycorrhizal plants. The MY and K treatments also increased the chlorophyll content and leaf area index by 57%. This study concluded that application of potassium and mycorrhizal fungi enhanced glomalin production and increased plant resistance to heavy metal stress. [ABSTRACT FROM AUTHOR]

Much of our knowledge of plant growth in response to soil nutrient supply comes from studies under homogeneous soil conditions. However, the adoption of reduced or nil tillage and shallow banding of fertilisers at the time of seeding causes spatially variable distribution and availability of soil nutrients in agricultural lands. Soil available nutrients, particularly the poorly mobile ones such as phosphorus (P), potassium (K), zinc (Zn), manganese (Mn), and copper (Cu), stratify within the fertilised topsoil. In water-limited environments where the topsoil is prone to drying, soil nutrient stratification may influence nutrient availability and plant uptake because of impeded root growth or reduced diffusion of immobile nutrients to the root surface, or more likely a combination of both factors. Placing fertilisers deeper in the soil profile could increase nutrient acquisition and utilisation by plants as fertiliser nutrients are in the moist soil for a longer part of the growing season. However, the effectiveness of deep placement of fertilisers may also be determined by soil texture, tillage, fertilising history, nutrient mobility, and crop species. In Mediterranean-type climates of southern Australia, a yield response of winter crops to deep fertiliser mostly occurs on infertile sandy soils in low rainfall regions. This contrasts with the responses of winter and summer crops in northern Australia on soils with optimum-to-high nutrients but subjected to rapid and frequent drying of topsoil because of high temperatures and high evaporation demand during the growing season. The pattern of nutrient accumulation by crop species (indeterminate v. determinate) and the mobility of mineral nutrients in the phloem would also modify the effectiveness of deep-placed nutrients under drought. The complexity of plant responses to subsoil nutrition may suggest that before adopting deep fertiliser practice in a paddock it is essential to understand the effects of edaphic and climatic conditions, soil management, and plant-soil interactions in order to achieve maximum yield benefit. Additional keywords: soil nutrient heterogeneity, dry surface soil, subsoil nutrition, nutrient acquisition, crop growth, grain yield., Introduction In modern agriculture, vertical stratification of soil nutrients is thought to be widespread as a result of the increased adoption of minimum- or no-till farming systems, which minimise or [...]

Application of exogenous cytokinin [N.sup.6]-benzylaminopurine (BAP) to flowers at anthems increases pod set but not grain yield in lupins (Lupinus angustifolius L). This study aimed to examine whether supplemental nitrogen supply could enhance the fulfilment of enlarged sink capacity induced by BAP application and thus increase seed yield. An abscission-minus lupin mutant (cv. Danja) was grown in pots under [glasshouse conditions. Application of BAP to all flowers produced more pods on the main stem, but not on the lateral branches, with four to 13 more total pods set on the BAP-treated plants than on the control plants. When BAP was applied to main stem flowers only, the number of pods on the main stem increased from four to 18, but pods on the lateral branches decreased from 19 to 11. In contrast, when BAP was applied to lateral flowers only, the number of pods on the lateral branches increased. However, the increase in pod set induced by BAP caused a decrease in the number of seeds per pod and average seed weight, and as a consequence, plant seed yield was not affected by BAP. Urea fertilizer caused much more shoot N accumulation than did symbiotic [N.sub.2] fixation, but this shoot N enrichment did not result in an increase in seed yield or seed N content. These findings indicate that there is a limit to grain yield and N harvest index in lupins. Although exogenous application of cytokinin can increase sink strength and cause a redistribution of yield components between the main stem and lateral branches, it did not increase the grain yield of the whole plant under these experimental conditions., GRAIN YIELD and harvest index of narrow-leafed lupin are highly variable and even crops with good vegetative growth sometimes yield poorly. Factors causing the seasonal variability of grain yield and [...]

Aims: There is still limited information about the dynamics of potassium (K) uptake and use over the growth cycle in cereals, but quantification of such relationships is necessary to model crop response to K and improve K fertiliser practice. This study examined the effects of varying K supply on K use efficiency, leaf gas exchange, root and shoot growth at successive stages of plant phenological development, and on seed yield in wheat ( Triticum aestivum L.). Methods: The study was conducted with a low-K loamy sand in a naturally-lit glasshouse. Six rates of soil K were applied as 15, 22.5, 30, 45, 75, 135 mg K kg −1, and six harvests were made to assess growth responses at different stages. Results: Tiller development, shoot dry weight, leaf photosynthesis and transpiration efficiency were closely related to soil K supply with time. Plants with 15 to 45 mg K kg −1 had lower root-to-shoot ratio than those supplied with 75 or 135 mg K kg −1. Plants showed maximal K accumulation in shoots prior to anthesis regardless of K rates, but K use efficiency differed during growth among the treatments. Adequate K supply enhanced seed yield by increasing ear numbers, single seed weight and harvest index. Conclusions: The rates of K supply affect K use efficiency, the root-to-shoot ratio and seed yield in wheat with a key feature of growth on a low-K sand as active K uptake during vegetative growth and subsequent reliance on K redistribution for reproductive growth. The poor adaptation of root growth to K deficiency may impair the plant’s ability for nutrient acquisition especially in water limited environment. [ABSTRACT FROM AUTHOR]