Nonexchangeable Potassium Displacement in Relation to Potassium Availability to Rainfed Maize under Nitrogen Fertilization

A study was conducted to evaluate the effect of nitrogen (N) application, through an easily available and cheap source urea, on potassium (K) displacement and its availability in K-deficient maize-growing soils of rainfed subtropics. The greatest amount of K was displaced (11.22 kg ha^?1) by N application at the rate of 80 kg N ha^?1 (treatment T₄). Amount of N fixed to displace K (11.10 kg ha^?1) was also greatest in the same treatment. Displaced K was positively related to nonexchangeable potassium (NEK) release. Nitrogen application through urea at 80 kg ha^?1 helped not only in meeting N requirement of maize crop in these N-deficient soils but can also satisfy the K requirements (as these soils are low in K) of these soils. Potassium displacement also increased the production efficiency of the maize crop by promoting its relative production efficiency index (RPEI) from suitability class V to class III.     

Coronatine‐induced lateral‐root formation in cotton (Gossypium hirsutum) seedlings under potassium‐sufficient and ‐deficient conditions in relation to auxin

A large root system plays a decisive role in potassium (K)‐acquisition efficiency of cotton. Coronatine (COR), a non‐host‐specific phytotoxin, may affect the auxin level in plants and might therefore be useful in regulating lateral‐root (LR) development. Our objectives were (1) to examine the effects of COR on root development, especially the LR formation in hydroponically grown cotton seedlings, and (2) to explore possible mechanisms involved. The results showed that K deficiency (0.05 mM) significantly reduced LR formation in cotton seedlings, possibly due to the decrease of endogenous indole acetic acid (IAA) in roots by more than half. Following the application of 10 nM COR, the LRs significantly increased by 26% in K‐sufficient (0.5 mM) solution and by 95% in K‐deficient solution. Although COR did not increase the free IAA level in the primary root, the polar auxin‐transport inhibitor N‐1‐naphthylphthalamic acid (NPA) decreased its stimulating effects on LR formation by 25%–30%, suggesting that the COR‐induced LR formation was independent of increased auxin level but likely associated with auxin transport. Treatment of plants with 1‐naphthalene acetic acid (NAA) increased LR formation at NAA concentrations of 100 nM, but had no effect at 10 nM. In the presence of 1 nM COR, however, NAA increased LR formation at 10 nM concentrations. This indicates that LR formation due to COR possibly involves changes in auxin sensitivity. In addition, the shorter LRs of COR‐treated seedlings were clearly restored when COR was removed from solutions for 12 d, and the total root length, total root surface area as well as K uptake increased significantly, suggesting that COR may be potentially useful for enhancing the K‐acquisition efficiency of cotton seedlings.     

Potassium balances for arable soils in southern England 1986–1999

Abstract. The behaviour of potassium (K) in a range of arable soils was examined by plotting the change in exchangeable K of the topsoil (Δ K_ex) at the end of a 3–5 year period against the K balance over the same period (fertilizer K applied minus offtake in crops, estimated from farmers' records of yield and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops MAFF 2000) are valid averages, 10–50% of Δ K_ex was explained by the balance, relationships being stronger on shallow/stony soils. Excess fertilizer tended to increase K_ex and reduced fertilization decreased it, requiring between 1.2 and 5.4 kg K ha⁻¹ for each mg L⁻¹Δ K_ex. However, merely to prevent K_ex falling required an extra 20 kg K ha⁻¹ yr⁻¹ fertilizer on Chalk soils and soils formed in the overlying Tertiary and Quaternary deposits, despite clay contents >18%. Whereas, on older geological materials, medium soils needed no extra K and clays gained 17 kg K ha⁻¹ yr⁻¹. It is unlikely that the apparent losses on some soil types are anomalies due to greater crop K contents. Theory and the literature suggest leaching from the topsoil as a major factor; accumulation in the subsoil was not measured. Recommendations for K fertilization of UK soils might be improved by including loss or gain corrections for certain soil types.     

Potassium efficiency mechanisms of wheat,barley, and sugar beet grown on a K fixing soil under controlled conditions

Plant species differ in their potassium (K) efficiency, but the mechanisms are not clearly documented and understood. Therefore, K efficiency of spring wheat, spring barley, and sugar beet was studied under controlled conditions on a K fixing sandy clay loam. The effect of four K concentrations in soil solution ranging from low (5 and 20 μM K) to high (2.65 and 10 mM K) on plant growth and K uptake was investigated at 3 harvest dates (14, 21, and 31 days after sowing). The following parameters were determined: shoot dry matter (DM), K concentration in shoot dry matter, root length (RL), root length/shoot weight ratio (RSR), shoot growth rate/average root length ratio (GR_s/aRL), K influx, and soil solution K concentrations. Wheat proved to have a higher agronomic K efficiency than barley and sugar beet, indicated by a greater relative yield under K‐deficient conditions. As compared to both cereals, sugar beet was characterized by higher K concentrations in the shoot dry matter, only 30—50 % of the root length, 15—30 % of the RSR and a 3 to 6 times higher GR_s/aRL. This means that the shoot of sugar beet had a 3 to 6 times higher K demand per unit root length. Even at low K concentrations in the soil solution, sugar beet had a 7 to 10 times higher K influx than the cereals, indicating that sugar beet was more effective in removing low available soil K. Wheat and barley were characterized by slow shoot growth, low internal K requirement, i.e. high K utilization efficiency, and high RSR, resulting in a low K demand per unit root length. At low soil K concentrations, both cereals increased K influx with age, an indication of adaptation to K deficiency. The mechanism of this adaptation merits closer investigation. Model calculations were performed to estimate the K concentration difference between the bulk soil and the root surface (ΔC_L) needed to drive the measured K influx. For the two cereals, the calculated ΔC_L was smaller than the K concentration in the soil solution, but for sugar beet, ΔC_L was up to seven times higher. This indicates that sugar beet was able to mobilize K in the rhizosphere, but the mechanisms responsible for this mobilization remain to be studied.     

The potential of glauconitic sandstone as a potassium fertilizer for olive plants

This study evaluated the potential of glauconitic sandstone as a fertilizer for supplying potassium to plants. The glauconite sandstone (Maraveh, Iran), as analyzed by X-ray fluorescence, was composed of 2.24% potassium oxide plus high contents of silicon, aluminum and ferric oxide. One-year old olive trees, Olea europaea L., were grown in sand or hydroponic culture in a greenhouse under three potassium treatments. Modified Hoagland nutrient solutions based on potassium treatments including 0.5 mM K⁺, 5 mM K⁺ and 400 g glauconitic sandstone powders (per 10 L in hydroponics and per 2.5 L in sand instead of K⁺ supply) were used in both cultures. Plants grown under the three different potassium treatments did not show any potassium deficiency symptoms. In the sand culture, growth and potassium content were higher in plants fed with 5 mM potassium than with the other two potassium treatments. Growth retardation and decreased potassium content in plants fed with 0.5 mM potassium were more severe in the hydroponic culture than in the sand culture. However, plants fed with 400 g glauconitic sandstone showed higher growth in the hydroponic culture than the sand culture. Thus, glauconitic sandstone has the ability to release potassium and can be utilized in combination with other potassium fertilizers.     

Consequences of sodium exclusion for the osmotic potential in the rhizosphere – Comparison of two maize cultivars differing in Na+ uptake

According to the biphasic model of growth response to salinity, growth is first reduced by a decrease in the soil osmotic potential (Ψ_o), i.e., growth reduction is an effect of salt outside rather than inside the plant, and genotypes differing in salt resistance respond identically in this first phase. However, if genotypes differ in Na⁺ uptake as it has been described for the two maize cultivars Pioneer 3906 and Across 8023, this should result in differences in Na⁺ concentrations in the rhizosphere soil solution and thus in the concentration of salt outside the plant. It was the aim of the present investigation to test this hypothesis and to investigate the effect of such potential differences in soil Ψ_o caused by Na⁺ exclusion on plant water relations. Sodium exclusion at the root surface of intact plants growing in soil was investigated by sampling soil solution from the rhizosphere of two maize cultivars (Across 8023, Pioneer 3906). Plants were grown in a model system, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). Across 8023 accumulated higher amounts of sodium in the shoot compared to the excluder (Pioneer 3906). The lower Na⁺ uptake in the excluder was partly compensated by higher K⁺ uptake. Pioneer 3906 not only excluded sodium from the shoot but also restricted sodium uptake more efficiently from roots relative to Across 8023. This was reflected by higher Na⁺ concentrations in the rhizosphere soil solution of the excluder 34 days after planting (DAP). The difference in Na⁺ concentration in rhizosphere soil solution between cultivars was neither due to differences in transpiration and thus in mass flow, nor due to differences in actual soil water content. As the lower Na⁺ uptake of the excluder (Pioneer 3906) was only partly compensated by increased uptake of K⁺, soil Ψ_o in the rhizosphere of the excluder was more negative compared to Across 8023. However, no significant negative effect of decreased soil Ψ_o on plant water relations (transpiration rate, leaf Ψ_o, leaf water potential, leaf area) could be detected. This may be explained by the fact that significant differences in soil Ψ_o between the two cultivars occurred only towards the end of the experiment (27 DAP, 34 DAP).     

Physical properties of a Luvisol for different long‐term fertilization treatments: II. Microscale behavior and its relation to the mesoscale

We determined the impact of different fertilization, namely organic vs. mineral fertilization, on the mesoscale parameter cyclic compressibility as well as on rheology of soil samples as a microscale parameter and how these parameters are related. Therefore, undisturbed samples were taken from a long‐term fertilization trial at the Dikop farm near Bonn (Germany) and tested for their mechanical and hydraulic properties. This paper examines the sensitivity of the soil towards cyclic loading (mesoscale) and oscillatory shearing at the microscale by means of an amplitude sweep test and the resulting parameter maximum shear stress. Fertilization increased cyclic compressibility and thus revealed structural weakness of fertilized soil samples, so did shear stress at the microscale. The main reason for this was a decrease in bulk density in the wake of fertilization. However, within the range of fertilized soil samples, the soil structure became less susceptible towards cyclic loading and oscillatory shearing, respectively, the more organic matter the soil contained (equivalent to the fertilization level). This was assumedly caused by enhanced cementation due to organic substances that could partly substitute the direct grain–grain contacts generally contributing to soil strength. The similar behavior of cyclic compressibility and maximum shear stress enabled a first approach to relate soil mechanical parameters at the microscale to those at the mesoscale.     

When is a habitat not a habitat? Dramatic resource use changes under differing weather conditions for the butterfly Plebejus argus

A key to conserving organisms is identification of the habitat bounds and essential resources within them. In population studies (metapopulations) of phytophagous arthropods it is tacitly assumed that habitat bounds portray short-term stability and that habitat is largely synonymous with hostplant areas or with a single vegetation unit comprising hostplants; structural components are usually ignored. We test these assumptions by monitoring the behaviour and relative abundance of Plebejus argus (L.) (Lepidoptera: Lycaenidae) in relation to changing weather conditions in two patches of a North Wales metapopulation for the butterfly. Our findings confirm the importance of structural habitat components. P. argus density is higher in the vicinity of shrubs which are used for roosting, resting, basking, mate location and shelter. A dominant proportion of the population adopts shrub areas in cooler, cloudy and windy weather. In warmer, sunnier and calmer conditions, the butterfly spends longer in flight and moves out onto calcareous heath dominated by hostplants. In doing so, an increasing, even dominant, proportion of the population occupies exposed slopes adjacent to and above shrub covered areas associated with the hostplant. In effect, the habitat bounds appear to change with conditions on scales of days and hours. What part of a landscape may be defined as a habitat, and what part of it may appear to be most important for an organism, depends on just when and where surveys are carried out. We argue that for correct delineation of habitats attention needs to be given to resource use in different conditions. In the face of enhanced global warming, a broad view should be taken of arthropod habitats that considers the resources required for varying conditions.     

Novel lysimeter techniques — a basis for the improved investigation of water,gas, and solute transport in soils

For many years lysimeters have been proven to be effective tools in assessing and predicting the effects of current land use and future land use changes in catchment areas on both water and solute balances. Although due to the diverse aspects of mass transport modelling, many different types of lysimeters exist, water and solute balances are by no means fully understood, especially in post‐mining areas. To tackle this problem, a new piece of equipment has been developed which enables the actual weight of a lysimeter to be precisely measured. The newly designed device, which has been used for one of the experiments described in this paper, permits the weighing of for example a 2 m³ lysimeter vessel with an accuracy down to 30 g. The second newly developed appliance presented here is the GAMS (Gas‐Migration‐Simulator). Basically comparable to a lysimeter, the difference is that the GAMS allows the detailed investigation of soil‐gas migration processes and their dependence on parameters like the diffusion coefficient and the gas permeability of the soil, alterations of the groundwater level and on various external influences such as changes of the actual meteorological conditions. These two newly developed techniques are described in this paper, and their respective suitability is demonstrated on the basis of data sets recorded during initial experiments.     

Incorporating uncertainty about species’ potential distributions under climate change into the selection of conservation areas with a case study from the Arctic Coastal Plain of Alaska

This analysis presents a conservation planning framework for decisions under uncertainty and applies it to the Arctic Coastal Plain of Alaska. Uncertainty arises from variable distributional shifts of species’ ranges due to climate change. The planning framework consists of a two-stage optimization model that selects a nominal conservation area network in the first stage and evaluates its performance under the climate scenarios in the second stage. The model is applied to eleven at-risk species in Alaska including the threatened Spectacled Eider and Steller’s Eider sea ducks and the polar bear. The 109th United States Congress and 2008 federal budget proposed opening for oil and gas development the “1002 Area” of the Arctic National Wildlife Refuge, which intersects the Plain. This analysis finds that, if Arctic Alaska experiences 1.5 °C of warming by 2040 (as predicted by the Intergovernmental Panel on Climate Change’s A2 scenario), then potential habitat will decrease significantly for eight of these at-risk species, including the polar bear. This analysis also shows that there is synergism between oil and gas development and climate change. For instance, climate change accompanied by no development of the 1002 Area results in an increase of potential habitat for Steller’s Eider. However, if development accompanies climate change, then there is a 20% decrease in that area. Further, this analysis quantifies the tradeoff between development and maintenance of suitable habitat for at-risk species.     

Developing nitrogen management strategies under drip fertigation for wheat and maize production in the North China Plain based on a 3‐year field experiment

The intensive winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) cropping systems in the North China Plain (NCP) rely on the heavy use of mineral nitrogen (N) fertilizers. As the fertigated area of wheat and maize in the NCP has grown rapidly during recent years, developing N management strategies is required for sustainable wheat and maize production. Field experiments were conducted in Hebei Province during three consecutive growth seasons in 2012–2015 to assess the influence of different N fertigation rates on N uptake, yield, and nitrogen use efficiency [NUE: recovery efficiency (RE_N) and agronomic efficiency (AE_N)]. Five levels of N application, 0 (FN₀), 40 (FN_40%), 70 (FN_70%), 100 (FN_100%), and 130% (FN_130%) of the farmer practice rate (FP: 250 kg N ha^?1 and 205.5 kg N ha^?1 for wheat and maize, respectively), corresponding to 0, 182.2, 318.9, 455.5, and 592.2 kg N ha^?1 y^?1, respectively, were tested. Nitrogen in the form of urea was dissolved in irrigation water and split into six and four applications for wheat and maize, respectively. In addition, the treatment “drip irrigation + 100% N conventional broadcasting” (DN_100%) was also conducted. All treatments were arranged in a randomized complete block design with three replications. The results revealed the significant influence of both N fertigation rate and N application method on grain yield and NUE. Compared to DN_100%, FN_100% significantly increased the 3‐year averaged N recovery efficiency (RE_N) by 0.09 kg kg^?1 and 0.04 kg kg^?1, and the 3‐year averaged N agronomic efficiency (AE_N) by 2.43 kg kg^?1 and 1.62 kg kg^?1 for wheat and maize, respectively. Among N fertigation rates, there was no significant increase in grain yield in response to N applied at a greater rate than 70% of FP due to excess N accumulation in vegetative tissues. Compared to FN_70%, FN_100%, and FN_130%, FN_40% increased the RE_N by 0.17–0.57 kg kg^?1 and 0.03–0.34 kg kg^?1and the AE_N by 4.60–27.56 kg kg^?1 and 2.40–10.62 kg kg^?1 for wheat and maize, respectively. Based on a linear‐response relationship between the N fertigation rate and grain yield over three rotational periods it can be concluded that recommended N rates under drip fertigation with optimum split applications can be reduced to 46% (114.6 kg N ha^?1) and 58% (116.6 kg N ha^?1) of FP for wheat and maize, respectively, without negatively affecting grain yield, thereby increasing NUE.