Cynthia A. Grant

Cadmium accumulation in crops

Cadmium is a heavy metal present in soils from natural and anthropogenic sources. Plant uptake of Cd at levels present in the soil solution is dependent on a system that is largely metabolically mediated and competitive with the uptake system for Zn and possibly other metals. Much of the Cd taken up by plants is retained in the root, but a portion is translocated to the aerial portions of the plant and into the seed. The amount of Cd accumulated and translocated in plants varies with species and with cultivars within species. Soil, environmental and management factors impact on the amount of Cd accumulated in plants. Potential methods of reducing the accumulation of Cd in crops include reduction of Cd input to the soil system, site selection, management practices which decrease the concentration of Cd in the soil solution and its uptake and translocation by plants, and development and production of plant cultivars with the genetic tendency for low Cd uptake. Key words: Cadmium, fertilizers, genetics, upta...

The importance of early season phosphorus nutrition

A review of studies conducted in a range of plant species indicated the importance of an adequate supply of P during early crop growth and outlined plant adaptations for accessing early season P. Potential implications of the requirement for early season P in the development of management practices to optimize P supply for crop production were also discussed. Phosphorus plays a critical role in energy reactions in the plant. Deficits can influence essentially all energy requiring processes in plant metabolism. Phosphorus stress early in the growing season can restrict crop growth, which can carry through to reduce final crop yield. Deficiencies during early growth generally have a greater negative influence on crop productivity than P restrictions imposed later in growth. Plants respond to P deficiencies by adaptations that increase the likelihood of producing some viable seed. The adaptations increase the ability of the plant to access and accumulate P and include modification of rhizosphere pH, diversio...

Differential response of weed species to added nitrogen

Abstract Information on responses of weeds to various soil fertility levels is required to develop fertilizer management strategies as components of integrated weed management programs. A controlled environment study was conducted to determine shoot and root growth response of 23 agricultural weeds to N fertilizer applied at 0, 40, 80, 120, 180, or 240 mg kg−1 soil. Wheat and canola were included as control species. Shoot and root growth of all weeds increased with added N, but the magnitude of the response varied greatly among weed species. Many weeds exhibited similar or greater responses in shoot and root biomass to increasing amounts of soil N, compared with wheat or canola. With increasing amounts of N, 15 weed species showed a greater increase in shoot biomass, and 8 species showed a greater increase in root biomass, compared with wheat. Ten weed species exhibited increases in shoot biomass similar to that exhibited by canola, and five weed species showed greater increases in root biomass than did canola, as N dose was increased. All crop and weed species extracted > 80% of available N at low soil N levels. At the highest N dose, 17 of 23 weed species took up similar or greater amounts of soil N than did wheat, and 6 weed species took up N in amounts similar to that taken up by canola. These findings have significant implications as to how soil fertility affects crop–weed competition. The high responsiveness of many weed species to N may be a weakness to be exploited through development of fertilizer management methods that enhance crop competitiveness with weeds. Nomenclature: Canola, Brassica napus L. ‘Excel’; spring wheat, Triticum aestivum L. ‘Katepwa’.

Nitrogen fertilization management for no-till cereal production in the Canadian Great Plains: a review

Nitrogen (N) is the nutrient most limiting crop production in all areas of the world and is generally applied to soil in the largest quantity. A review of the research on N fertilization management for no-till cereal production in the Canadian Great Plains, on mainly Chernozem and Gray soils, was done to illustrate the management practices which can be used to optimize the N use efficiency so as to minimize the N loss from root zone and environmental damage. Applied N is subject to loss by volatilization, immobilization, denitrification and leaching in soil and its efficiency of use by plants is governed by soil and climatic factors, fertilizer material, and soil, crop and fertilizer management practices. Overall efficiency of applied N has been <70%. Reducing tillage intensity modifies both the demand of crops for N due to changes in yield potential, and the supply of N due to changes in N cycling and losses. Consequently, it may be necessary to compensate for this by adjusting the fertilizer rate. Fertilizer use efficiency may also change with changes in tillage management, microclimate, microbial activity and distribution of fertilizer relative to crop residue. Placing the fertilizer in a band reduces contact with soil microorganisms, reducing immobilization of both ammonium (NH4) and nitrate (NO3). Banding also slows the conversion of urea to NH3 and NH4 to NO3, which can reduce losses by denitrification and leaching. The use of the urease inhibitor n-(n-butyl) thiophosphoric triamide (NBPT) shows promise in improving the efficiency of surface-applied urea-containing fertilizers in no-till systems and reducing seedling damage from seed-placed fertilizers. Ultimately, any N fertilization package has advantages and disadvantages. In selecting the optimum fertilizer management system for a farming operation, the balance between rate of application, cost and availability of equipment, soil disturbance, seedbed quality, moisture conservation, time and labor constraints and fertilizer use efficiency must be considered. The “best” management system is not fixed, but depends on the major limiting factors on each individual farm.

Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development

Plants require adequate P from the very early stages of growth for optimum crop production. Phosphorus supply to the crop is affected by soil P, P fertilizer management and by soil and environmental conditions influencing P phytoavailability and root growth. Phosphorus uptake in many crops is improved by associations with arbuscular mycorrhizal fungi. Cropping system and long-term input of P through fertilizers and manures can influence the amount and phytoavailability of P in the system and the development of mycorrhizal associations. Optimum yield potential requires an adequate P supply to the crop from the soil or from P additions. Where early-season P supply is low, P fertilization may improve P nutrition and crop yield potential. Alternately, under low-P conditions, encouragement of arbuscular mycorrhizal associations may enhance P uptake by crops early in the growing season, improving crop yield potential and replacing starter fertilizer P applications. Soil P supply that exceeds P requirements of t...

Ammonia volatilization from soils fertilized with urea and varying rates of urease inhibitor NBPT

Loss of N as ammonia (NH3) from surface-applied urea fertilizer may be high if hydrolysis takes place at the soil surface. The urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) may reduce NH3 loss from urea by delaying hydrolysis. Field studies using surface chambers were conducted in 1996 and 1997 to compare the amount of NH3 volatilized from surface applications of granular urea (100 kg N ha–1) treated with varying concentrations of NBPT (0, 0.05, 0.10 and 0.15% NBPT wt/wt). The studies were conducted on two Orthic Black Chernozemic soils, a Stockton fine sandy loam and a Newdale clay loam, in May and again in July to determine the relative influence of soil texture and temperature on NBPT performance at the varying rates. Ammonia losses were measured at various times to 12 d after fertilization (DAF) in 1996 and to 21 DAF in 1997. Total NH3 losses decreased in the order of 0% > 0.05% > 0.15% > 0.10% where use of NBPT reduced total NH3 loss by 28-88% over the entire study duration, and by 82 t...

Effects of phosphorus and zinc fertiliser management on cadmium accumulation in flaxseed

Field studies were conducted over 3 years on three soil types to evaluate the interactive effects of phosphate and zinc fertilisers on the concentration and accumulation of Cd in flaxseed. Flaxseed tends to accumulate high concentrations of Cd relative to cereal crops, which may be of concern when the flaxseed is entering the health-food market. Application of P, as monoammonium phosphate, increased Cd concentration and accumulation and decreased Zn concentration in flaxseed; the effect being greater with banded as compared to broadcast placement. Application of Zn, as zinc sulphate, generally decreased Cd concentration, but had little effect on Cd accumulation in flaxseed. Concentration of Cd in flaxseed decreased as seed concentration of Zn increased, across soil types and fertiliser treatments. Therefore, lower Zn concentration in the seed, whether due to low soil Zn levels, reduced Zn phytoavailability caused by P application or dilution of seed Zn due to increased dry matter production may be associated with increased Cd concentrations in flaxseed.

Effect of nitrogen application on concentration of cadmium and nutrient ions in soil solution and in durum wheat

A growth chamber experiment was conducted to study the effect of nitrogen fertilizer on the chemical composition of the soil solution over time, and to determine Cd uptake as a function of rates of nitrogen fertilizer application and transpiration. Sceptre durum wheat was grown in a fine sandy loam soil, in pots with treatments of 0, 50, 100, 200, 400, and 800 µg N g−1 as urea. The soil solution was removed by water displacement and analyzed for Cd and other nutrient ions at time of seeding, 10, 20, 30, and 40 d after seeding, and at the time of crop maturity. Soil samples were analyzed at each sampling time, and aboveground plant material was also harvested at these times and analyzed for Cd and other nutrient ions. Behaviour of Cd was compared to that of the nutrient ions to gain a better understanding of patterns of ion behaviour. Conductivity measurements were taken as estimators of ionic strength. Both solution Cd concentration and DTPA-extractable soil Cd increased significantly with increasing nitr...

Influence of fertilizer nitrogen source and management practice on N2O emissions from two Black Chernozemic soils

Fertilizer nitrogen use is estimated to be a significant source of nitrous oxide (N2O) emissions in western Canada. These estimates are based primarily on modeled data, as there are relatively few studies that provide direct measures of the magnitude of N2O emissions and the influence of N source on N2O emissions. This study examined the influence of nitrogen source (urea, coated urea, urea with urease inhibitor, and anhydrous ammonia), time of application (spring, fall) and method of application (broadcast, banded) on nitrous oxide emissions on two Black Chernozemic soils located near Winnipeg and Brandon Manitoba. The results of this 3-yr study demonstrated consistently that the rate of fertilizer-induced N2O emissions under Manitoba conditions was lower than the emissions estimated using Intergovernmental Panel on Climate Change (IPCC) coefficients. The Winnipeg site tended to have higher overall N2O emissions (1.7 kg N ha-1) and fertilizer-induced emissions (~0.8% of applied N) than did the Brandon si...

Inoculant formulation and fertilizer nitrogen effects on field pea: Nodulation, N2 fixation and nitrogen partitioning

Field pea (Pisum sativum L.) acreage has expanded rapidly in the past 10 yr in the Peace River Region of Alberta as well as western Canada. Understanding nitrogen dynamics of Rhizobium inoculants and applied N will provide farmers opportunities to improve N nutrition of field pea. Field experiments were conducted (a) to compare the effects of soil inoculation using granular inoculant, and seed inoculation using peat powder and liquid inoculants with an uninoculated check, on field pea nodulation and N2 fixation, and (b) to determine whether starter N is required by field pea to enhance N2 fixation. The effects of inoculant formulation on nodule number, N accumulation and N2 fixation were in the order: granular > peat powder > liquid = uninoculated. Field pea, from soil-applied inoculant, accumulated more N prior to and during podfilling than field pea with seed-applied inoculant. Fertilizer N application rates < 40 kg N ha-1 had no significant effects on biomass N at flatpod, indicating that starter N was...