Methods of reducing the soil acidification caused by nitrogen fertilizers

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A summary of placement and fall versus spring application of nitrogen fertilizers

Non-Peer ReviewedIn 52 field experiments since 1973-74, the yield of barley grain without N averaged 1570 kg/ha, but the yield was increased by fall and spring application of incorporated urea (56 kg N/ha) to 2540 and 3470 kg/ha, respectively. Early fall application was only half as efficient as late fall application. In five field experiments with 15N, the recovery in the spring of fall applied nitrate was low (13 to 60 %) while recovery of late fall banded ammonium was much higher (82 to 99 %). These losses came about through denitrification and not by leaching. Variable amounts of applied nitrate and ammonium were immobilized in the soil. Fall banding (45 cm spacing) and fall nesting (45 × 45 cm spacing) of urea (or aqua ammonia) gave larger yield increases than fall incorporation. In five experiments before 1978-79, yield increases of barley grain from fall application of urea by incorporation, banding and nesting were 960, 1240, and 1560 kg/ha, respectively. In the same order, yield increases were 740, 1100, and 1510 kg/ha in ten more recent experiments. However, the size of yield increases from fall banding were variable from experiment to experiment, ranging from being similar to fall incorporation to being similar to the high-yielding fall nests. With spring application of urea, banding produced slightly higher yields than incorporation, while nesting tended to produce lower yields. Retaining rather than removing the straw of the previous crop depressed the yield of barley grain by 650 kg/ha in six field experiments, and the retention of straw halved the uptake of fertilizer N by the crop. Preliminary results suggest that placement of fertilizer N in large pellets may overcome the immobilization of fertilizer N by the straw

Unconventional methods of fertilizer placement to reduce losses of fall applied nitrogen

Non-Peer ReviewedIn two field experiments conducted in 1978-79, fall application of incorporated urea, or banded aqua ammonia, produced much less increase in yield and N-uptake than did spring application for barley grain. However, when the fall-applied fertilizers were placed in constricted nests (one nest per each 45 x 45 cm area) the yield and N-uptake were nearly as great as with spring application. The mechanism by which nests avert losses from fall-applied N is through slowing of nitrification, and possibly through lessening of immobilization of fertilizer N by straw. Indirect evidence suggests that placement in nests is more effective than inhibitors of nitrification in reducing losses from fall-applied N fertilizers. The two field experiments in 1978-79, and three experiments in 1977-78 with fall-applied . urea showed that band placement improved yield in comparison to incorporation, but the banding was inferior to nesting. More specifically, yields with incorporation, banding, nesting, and spring incorporation were 960, 1240, 1560, and 1830 kg/ha, respectively. In the same order, values for % uptake of fertilizer N, were 31, 38, 53, and 66 %. Taking all of the eight experiments which have been conducted with nesting during the past four years, average yield increases were 1030, 1750, and 1980 kg/ha for fall incorporation, fall nesting, and spring incorporation, respectively. This work has been restricted to northern Alberta and northern Saskatchewan, and the feasibility of practical field-scale techniques of nesting, or application of large pellets, has not yet been investigated, but nevertheless the benefit of fall nesting is large enough to suggest work on this topic by other researchers in other areas of the prairie provinces

Influence of formulation of elemental S fertilizer on yield, quality, and S uptake of canola seed

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Influence of long-term applications of N and S fertilizers (1980-2005) on dry matter yield of grass and soil properties in a Dark Gray Chernozem in north-central Saskatchewan

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Storm-triggered landslides in the Peruvian Andes and implications for topography, carbon cycles, and biodiversity

In this study, we assess the geomorphic role of a rare, large-magnitude landslide-triggering event and consider its effect on mountain forest ecosystems and the erosion of organic carbon in an Andean river catchment. Proximal triggers such as large rain storms are known to cause large numbers of landslides, but the relative effects of such low-frequency, high-magnitude events are not well known in the context of more regular, smaller events. We develop a 25-year duration, annual-resolution landslide inventory by mapping landslide occurrence in the Kosñipata Valley, Peru, from 1988 to 2012 using Landsat, QuickBird, and WorldView satellite images. Catchment-wide landslide rates were high, averaging 0.076 % yr−1 by area. As a result, landslides on average completely turn over hillslopes every  ∼  1320 years, although our data suggest that landslide occurrence varies spatially and temporally, such that turnover times are likely to be non-uniform. In total, landslides stripped 26 ± 4 tC km−2 yr−1 of organic carbon from soil (80 %) and vegetation (20 %) during the study period. A single rain storm in March 2010 accounted for 27 % of all landslide area observed during the 25-year study and accounted for 26 % of the landslide-associated organic carbon flux. An approximately linear magnitude–frequency relationship for annual landslide areas suggests that large storms contribute an equivalent landslide failure area to the sum of lower-frequency landslide events occurring over the same period. However, the spatial distribution of landslides associated with the 2010 storm is distinct. On the basis of precipitation statistics and landscape morphology, we hypothesise that focusing of storm-triggered landslide erosion at lower elevations in the Kosñipata catchment may be characteristic of longer-term patterns. These patterns may have implications for the source and composition of sediments and organic material supplied to river systems of the Amazon Basin, and, through focusing of regular ecological disturbance, for the species composition of forested ecosystems in the region

Increasing biomass in Amazonian forest plots

A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 ± 0.43 Mg per hectare per year (ha-1 yr-1), where 1 ha = 104 m2), or 0.98 ± 0.38 Mg ha-1 yr-1 if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades

Fingerprinting the impacts of global change on tropical forests

Recent observations of widespread changes in mature tropical forests such as increasing tree growth, recruitment and mortality rates and increasing above-ground biomass suggest that 'global change' agents may be causing predictable changes in tropical forests. However, consensus over both the robustness of these changes and the environmental drivers that may be causing them is yet to emerge. This paper focuses on the second part of this debate. We review (i) the evidence that the physical, chemical and biological environment that tropical trees grow in has been altered over recent decades across large areas of the tropics, and (ii) the theoretical, experimental and observational evidence regarding the most likely effects of each of these changes on tropical forests. Ten potential widespread drivers of environmental change were identified: temperature, precipitation, solar radiation, climatic extremes (including El Niño Southern Oscillation events), atmospheric CO2 concentrations, nutrient deposition, O3/acid depositions, hunting, land-use change and increasing liana numbers. We note that each of these environmental changes is expected to leave a unique 'fingerprint' in tropical forests, as drivers directly force different processes, have different distributions in space and time and may affect some forests more than others (e.g. depending on soil fertility). Thus, in the third part of the paper we present testable a priori predictions of forest responses to assist ecologists in attributing particular changes in forests to particular causes across multiple datasets. Finally, we discuss how these drivers may change in the future and the possible consequences for tropical forests

Long-term tillage, straw, and N rate effects on quantity and quality of organic C and N in a Gray Luvisol soil

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