Competition of Plants and Microorganisms for Added Nitrogen in Different Fertilizer Forms in a Semi-Arid Climate

In nitrogen (N) -limited agricultural systems, a high microbial immobilization of applied fertilizer-N can limit its availability to plants. However, there is scarce information on the effect of the form of fertilizer used on the plant–microorganism competition in clay-rich soils under a severe semi-arid climate. In a field study, we investigated the wheat–microorganism competition after the direct application of NH415NO3 closely to seeds in arable fields in North Kazakhstan, documenting the effect of the use of liquid versus granular fertilizer and mini-tillage versus no-tillage. Our results barely showed any fertilizer-N translocation in the soil. Plants outcompete microorganisms for fertilizer-N during the vegetation period. Microbial-to-plant 15N ratios revealed a predominant fertilizer-15N uptake by plants. The strong competition for N was mainly related to the placement of the fertilizer close to the seeds. Moreover, the long time interval between fertilization and sampling enhanced the competition for N, meaning that previously microbially immobilized N became available to plants through the death of microorganisms and their subsequent mineralization. The fertilizer distribution between microorganisms and plants did depend on the form of fertilizer used, owing to the good solubility of granular fertilizer. The smaller fertilizer-N uptake under the no-tilling condition was probably due to the more intense soil compaction, which caused a reduction in plant growth. The application of fertilizer close to the seeds and the small fertilizer translocation during the vegetation period ultimately resulted in a high level of plant-N being derived from the fertilizer.

The effect of irrigation on nitrogen uptake and use efficiency of two willow (Salixspp.) biomass energy varieties

Hangs, R. D., Schoenau, J. J., Van Rees, K. C. J. and Knight, J. D. 2012. The effect of irrigation on nitrogen uptake and use efficiency of two willow ( Salix spp.) biomass energy varieties. Can. J. Plant Sci. 92: 563–575. Nitrogen (N) fertilizers historically have been applied to support increased productivity of purpose-grown willow (Salix spp.) biomass energy plantations. However, a frequently observed lack of willow growth response to added fertilizer N is often attributed to poor fertilizer use efficiency. The objective of this study was to determine the effect of irrigation on the recovery of broadcast15N-labelled fertilizer, applied during the final year of a 3-yr rotation, by two willow varieties. A split-split-plot experiment was established on a fertile heavy clay soil in Saskatoon, SK, Canada, which consisted of two willow varieties (Charlie and SV1), three irrigation treatments (no irrigation, 75%, and 100% field capacity), and two fertilization treatments (1× and 2× the recommended fertilizer rate of 100:30:80:20 N:P:K:S; kg ha−1). Irrigation increased fertilizer N uptake by Charlie, but had no effect on the amount taken up by SV1, which was attributed to greater N use efficiency of SV1 compared with Charlie when irrigated. Eighty-two percent of the applied fertilizer N was accounted for in the following sinks: 43% in the soil (0–60 cm), 31% in the willow tissues (i.e., stems, leaves, stump, and roots), 7% in the LFH layer, and <1% in the non-crop vegetation; the balance (approximately 18%) was presumed lost primarily through denitrification from the poorly drained soil, but possibly some may have leached below the root zone as well. Although the willow varieties accessed only a portion of the applied fertilizer N during the year of application, the majority of the residual fertilizer N was conserved within the production system and, therefore, remained available for willow uptake in subsequent years.

Fertilizer Uptake, Partitioning, and Recovery in Container- Grown Common Hackberry (Celtis occidentalis) Trees

Ammonium-nitrate (NH4NO3) double enriched with the 15N isotope (1.5 atom %) was used to evaluate fertilizer N recovery, N partitioning, and aboveground N status in container-grown common hackberry (Celtis occidentalis L.) trees back-filled with native soil at Arlington, Wisconsin and Lisle, Illinois, U.S. Treatments consisted of 0, 1.42 g N tree-1 (0.05 oz) and 4.27 g N tree-1 (0.15 oz), the area equivalent of 0, 0.49, and 1.47 kg N 100 m-2 (0, 1, and 3 lb N 1000 ft-2). Trees were harvested 14, 30, 60, and 90 days after fertilization. Fertilizer-induced changes in aboveground N status were significant only at the 4.27 g N tree-1 (0.15 oz) treatment level. The amount of fertilizer N recovered in aboveground tissues increased with rate of application. Fertilizer N was preferentially partitioned to foliage and current season stem wood. The percentage of fertilizer recovered in aboveground tissues did not differ between the application rates, ranging from 15%–25% at Arlington, WI, and 5%–9% at Lisle, IL. Frost damage to the foliage at Lisle, IL may have resulted in location differences in aboveground biomass which affected fertilizer N uptake and recovery. These data suggest fertilizer N accumulated in nontarget sinks and/or were lost from the site of application at both rates of application.

Nitrogen Uptake in a Range of Alternative Orchard Floor Management Systems

The percentage of N from fertilizer removed from the field by fruit trees is low. Overapplication of N in orchards has been a common practice and is a concern due to environmental and tree growth problems caused by excess N. Orchard floor management practices (OFMP) can improve the physical and chemical properties of the soil and may alter the soil biological community. Biological activity can affect mineralization rate and thus nutrient availability. The purpose of this study was to determine the effect of alternative OFMP on fertilizer N uptake. Research plots were located in Corvallis, Ore. (COR) (7-year-old `Fuji'), and Hood River, Ore. (HR) (3-year-old `Red Delicious'). Treatments were begun in 2001 in a split-plot completely randomized design with three replications. Main plot treatments were herbicide or cultivation. Subplot treatments were no amendment, bark mulch, compost, and barley/vetch mown and blown into the tree row. Depleted NH3SO4 was applied to single-tree replicates at budbreak. Trees were destructively harvested at harvest of 2003. At HR, the percentage of N derived from fertilizer (NDFF) was significantly lower in the whole tree, leaves, new wood, old wood, spurs, and roots of trees from compost than from unamended plots (P < 0.05). At COR, the NDFF in the leaves, fruit, new wood, spurs and roots was significantly lower in trees from compost plots than unamended plots (P < 0.05). The NDFF also tended to be lower in trees from bark mulch-treated plots than control plots, although differences were not always significant. Vetch/barley amendment resulted in NDFF similar to no amendment. There were no significant differences between the total N of trees from unamended and compost plots. Trees from compost-treated plots appear to be acquiring N from sources other than fertilizer.

Isotopic and Nonisotopic Estimation of Nitrogen Uptake Efficiency in Container-grown Woody Ornamentals

Cornus sericea L., Weigela florida (Bunge) A. DC., and Euonymus alatus (Thunb.) Sieb were grown outside in 3.8-L plastic containers for 345 days (1 Apr. 2001 to 11 Mar. 2002). Nitrogen (N) was applied at rates (NAR) of 25, 50, 100, 200, and 300 mg·L–1 and delivered as aqueous double-labeled 15N depleted NH4NO3 (min 99.95% atom 14N). In all species, root, shoot, and total plant dry weight increased with increasing NARs while root to shoot ratios decreased. Similarly, root, shoot, and total plant N increased with NAR for each species, and at each NAR more N was stored in the roots than in the shoots. Estimation of fertilizer N uptake determined by the total N method was higher for all species and at each NAR than estimation of N uptake determined by the fertilizer 15N tracer method. Fertilizer N uptake efficiency determined by the total N method was highest at 25 mg·L–1 and decreased as NARs increased. In contrast fertilizer N uptake efficiency determined by the fertilizer 15N tracer method was lowest at 25 mg·L–1 and increased or remained relatively constant as NARs increased. Differences in N uptake and N uptake efficiency can be attributed to overestimation by the total N method due to the inclusion of nonfertilizer N and underestimation by the fertilizer 15N tracer method due to pool substitution. Corrected N uptake efficiency values can be calculated by adjusting the original data (total N or 15N uptake) by the distance between the origin and the y intercept of the regression line representing the data.

Isotopic and Nonisotopic Estimation of Nitrogen Fertilizer Uptake in Container-grown Woody Ornamentals

Accurate methods for determining the fate and recovery of nitrogen (N) fertilizer applied to container-grown nursery crops are essential to comply with regulations and develop innovative fertilizer programs. The objectives of this study were (i) to use 15N techniques to determine the fate of fertilizer N, (ii) to compare nonisotopic and isotopic methods of determining N recovery, and (iii) to determine the relative importance of fertilizer and non-fertilizer N at rates of 25, 50, 100, 200, and 300 mg·L-1 in container-grown Euonymus alatus (Thunb.) Sieb., Cornus sericea L., and Weigela florida (Bunge) A. DC. In all species, root and shoot N increased with N rate, and at each rate more N was stored in the roots than in the shoots. Estimation of N recovery determined by the total N method (Kjeldahl N/applied N) was significantly higher for all species and at each N rate than estimation of N recovery determined by the labeled fertilizer N method (labeled N/total applied N). Increasing fertilizer rates up to 100 mg·L-1 resulted in increased uptake of N derived from other sources (NDFO). NDFO at low N concentrations was a significant portion of the total N in the plant. As a result, the difference in estimation of percent N recovery between each method was larger at lower N concentrations for all species. The nonisotopic total N method produces higher fertilizer N uptake estimates, as much as three to four times the isotopic based estimates, in container-grown plants at N concentrations of 25 mg·L-1. Actual fertilizer N loss increases dramatically from 25 to 300 mg·L-1 (due to dramatic increases in N applied), despite small gains in fertilizer N recovery efficiency.

Nitrogen competition using 15N between early successional plants and planted white spruce seedlings

The ability of noncrop plants to compete with white spruce (Picea glauca (Moench) Voss) seedlings for applied fertilizer N is not well understood. Therefore, the objective of this study was to examine the efficacy of fertilizer N uptake using 15N by planted white spruce seedlings and understory vegetation. Double 15N-labeled NH4NO3 was broadcast in 1-m2plots for control, disc-trenched, and disc-trenched + manual brushing treatments. The fate of applied 15N in white spruce and noncrop plants was determined at the end of the first two growing seasons. The major competitors for fertilizer 15N were Populus tremuloides Michx. and grasses during the first growing season, and Populus tremuloides, Epilobium angustifolium L., and Achillea millefolium L. during the second growing season. Disc-trenching plus manual brushing significantly increased the fertilizer use efficiency of white spruce seedlings by limiting competition; however, <1% of the applied fertilizer 15N was utilized by the spruce seedlings after two growing seasons. The ability of competing vegetation to absorb broadcast fertilizer N suggests that alternative fertilizer types and placements be investigated to increase N uptake by white spruce seedlings planted in the boreal mixedwood forest.

The course of fertilizer nitrogen uptake by rainfed sugarcane in Mauritius

SUMMARYThe patterns of N uptake and dry matter synthesis by sugarcane (Saccharum hybrid spp.) were studied at four locations in Mauritius with 15N–labelled ammonium sulphate (100 kg N/ha) applied either in a single dressing in September or in two split applications in September and the following February. More than 80% of the total N recovered at harvest (100–120 kgN/ha) was absorbed by the sugarcane during an active uptake period from October to January. Split application prolonged this active N uptake until April only and had no effect on dry matter accumulation. While total Nabsorbed by above-ground sugarcane showed no decline over time, 10–20 kg N/ha of the 15N–labelled N was lost from the green tops even when the N was applied on two occasions. The fertilizer N losses from above-ground sugarcane were, however, not evident when fertilizer N recovery with time was studied by the difference method. In view of the observed losses of fertilizer N from the aerial parts of sugarcane, measurement of fertilizer N recovery at harvest by the N isotope dilution technique underestimates fertilizer N uptake by sugarcane and attributes too large a fraction of N loss to denitrification/volatilization of NH3.

The recovery of 15N from labelled urea fertilizer in crop components of sugarcane and in soil profiles

Trash conservation measures associated with burnt and green harvested cane, and minimum tillage, are being adopted by canegrowers. These new management systems pose questions about how to apply N fertilizers. Experiments were conducted to evaluate the efficiency of fertilizer N uptake by the crop. Urea, labelled with 15N , was either broadcast or buried in three trash management systems: with and without trash after harvesting cane burnt, and with trash after harvesting cane green. The proportion of applied fertilizer-N recovered in a cane crop was 33% when labelled urea was buried, and 18% when broadcast. The presence of trash mulches from burnt or green harvested cane had negligible effects on the uptake of fertilizer-N. Of fertilizer-N applied, 25% was detected in soil 12 months after application, and there was no difference between burying and broadcasting urea. The fate of the lost fertilizer-N was not determined. Leaching did not appear to be a significant loss process in this gleyed podzolic soil, but ammonia volatilization probably occurred when urea was broadcast and it is suspected that denitrification accounted for the majority of the fertilizer-N losses.