Keith C. Cameron

Bio: Keith C. Cameron is an academic researcher from Lincoln University (New Zealand). The author has contributed to research in topics: Leaching (agriculture) & Nitrification. The author has an hindex of 56, co-authored 247 publications receiving 12175 citations. Previous affiliations of Keith C. Cameron include Canterbury of New Zealand & University of Reading.

Nitrate leaching in temperate agroecosystems: sources, factors and mitigating strategies

Abstract: Nitrate (NO3 −) leaching from agriculturalproduction systems is blamed for the rising concentrations ofNO3 − in ground- and surface-waters around the world.This paper reviews the evidence of NO3 − leachinglosses from various land use systems, including cut grassland, grazed pastures,arable cropping, mixed cropping with pasture leys, organic farming,horticultural systems, and forest ecosystems. Soil, climatic and managementfactors which affect NO3 − leaching are discussed.Nitrate leaching occurs when there is an accumulation ofNO3 − in the soil profile that coincides with or isfollowed by a period of high drainage. Therefore, excessive nitrogen (N)fertilizer or waste effluent application rates or N applications at the wrongtime (e.g. late autumn) of the year, ploughing pasture leys early in the autumn,or long periods of fallow ground, can all potentially lead to highNO3 − leaching losses. N returns in animal urine havea major impact on NO3 − leaching in grazed pastures.Of the land use systems considered in this paper, the potential for causingNO3 − leaching typically follow the order: forest< cut grassland < grazed pastures, arable cropping < ploughing ofpasture < market gardens. A range ofmanagement options to mitigate NO3 − leaching isdescribed, including reducing N application rates, synchronizing N supply toplant demand, use of cover crops, better timing of ploughing pasture leys,improved stock management, precision farming, and regulatory measures. This isfollowed by a discussion of future research needs to improve our ability topredict and mitigate NO3 − leaching.

Nitrogen losses from the soil/plant system: a review

Abstract: Losses of nitrogen from the soil/plant system not only reduce soil fertility and plant yield but can also create adverse impacts on the environment. Ammonia emissions into the atmosphere contribute to acid rain and represent an indirect source of nitrous oxide greenhouse gas emissions. Nitrate leaching losses into rivers and lakes can cause eutrophication resulting in excessive growth of aquatic weeds and algae, which can reduce fish populations and the recreational value of the water. Nitrate contamination of drinking water supplies can cause health risks. Legislation that is designed to limit nitrate leaching losses from land has become a constraint on agricultural land use in many countries. Nitrous oxide emissions into the atmosphere contribute to the depletion of the ozone layer and also make a significant contribution to climate change. This review describes the nitrogen cycle in temperate soil/plant systems, the processes involved in each of the individual nitrogen loss pathways, the factors affecting the amounts of losses and the methods that are available to reduce these losses. The review has shown that careful management of temperate soil/plant systems using best management practices and newly developed technologies can increase the sustainability of agriculture and reduce its impact on the environment.

Nitrification driven by bacteria and not archaea in nitrogen-rich grassland soils

Abstract: The oxidation of ammonia to nitrate, known as nitrification, is a key process in the nitrogen cycle. Real-time polymerase chain-reaction measurements show that nitrification is driven by bacteria rather than archaea in nitrogen-rich grassland soils in New Zealand. The oxidation of ammonia to nitrate, nitrification, is a key process in the nitrogen cycle. Ammonia-oxidizing archaea are present in large numbers in the ocean1,2,3 and soils4,5,6, suggesting a potential role for archaea, in addition to bacteria, in the global nitrogen cycle7,8. However, the importance of archaea to nitrification in agricultural soils is not well understood4. Here, we examine the contribution of ammonia-oxidizing archaea and bacteria to nitrification in six grassland soils in New Zealand using a quantitative polymerase chain reaction. We show that although ammonia-oxidizing archaea are present in large numbers in these soils, neither their abundance nor their activity increased with the application of an ammonia substrate, suggesting that their abundance was not related to the rate of nitrification. In contrast, the number of ammonia-oxidizing bacteria increased 3.2–10.4-fold and their activity increased 177-fold, in response to ammonia additions. Indeed, we find a significant relationship between the abundance of ammonia-oxidizing bacteria and the rate of nitrification. We suggest that nitrification is driven by bacteria rather than archaea in these nitrogen-rich grassland soils.

The use of a nitrification inhibitor, dicyandiamide (dcd), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract: In grazed dairy pasture systems, a major source of NO - 3 leached and N 2 O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO - 3 leaching and N 2 O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free-draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO - 3 -N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO - 3 -N leaching loss in a grazed paddock from 118 to 46 kg N ha -1 yr -1 . The NO - 3 -N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L -1 , with the latter being below the drinking water guideline of 11.3 mg N L -1 . Total N 2 O emissions following two urine applications were reduced from 46 kg N 2 O-N ha -1 without DCD to 8.5 kg N 2 O-N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha -1 yr -1 . The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO - 3 leaching and N 2 O emissions.

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Soil organic carbon sequestration rates by tillage and crop rotation : A global data analysis

Abstract: Changes in agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO 2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 ± 14 g C m -2 yr -1 , excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 ± 12 g C m -2 yr -1 , excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine max L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.

Nitrous oxide emissions from soils: how well do we understand the processes and their controls?

Abstract: Although it is well established that soils are the dominating source for atmospheric nitrous oxide (N2O), we are still struggling to fully understand the complexity of the underlying microbial production and consumption processes and the links to biotic (e.g. inter- and intraspecies competition, food webs, plant–microbe interaction) and abiotic (e.g. soil climate, physics and chemistry) factors. Recent work shows that a better understanding of the composition and diversity of the microbial community across a variety of soils in different climates and under different land use, as well as plant–microbe interactions in the rhizosphere, may provide a key to better understand the variability of N2O fluxes at the soil–atmosphere interface. Moreover, recent insights into the regulation of the reduction of N2O to dinitrogen (N2) have increased our understanding of N2O exchange. This improved process understanding, building on the increased use of isotope tracing techniques and metagenomics, needs to go along with improvements in measurement techniques for N2O (and N2) emission in order to obtain robust field and laboratory datasets for different ecosystem types. Advances in both fields are currently used to improve process descriptions in biogeochemical models, which may eventually be used not only to test our current process understanding from the microsite to the field level, but also used as tools for up-scaling emissions to landscapes and regions and to explore feedbacks of soil N2O emissions to changes in environmental conditions, land management and land use.

Stoichiometry of soil enzyme activity at global scale

Abstract: Extracellular enzymes are the proximate agents of organic matter decomposition and measures of these activities can be used as indicators of microbial nutrient demand. We conducted a global-scale meta-analysis of the seven-most widely measured soil enzyme activities, using data from 40 ecosystems. The activities of b-1,4-glucosidase, cellobiohydrolase, b-1,4-N-acetylglucosaminidase and phosphatase g )1 soil increased with organic matter concentration; leucine aminopeptidase, phenol oxidase and peroxidase activities showed no relationship. All activities were significantly related to soil pH. Specific activities, i.e. activity g )1 soil organic matter, also varied in relation to soil pH for all enzymes. Relationships with mean annual temperature (MAT) and precipitation (MAP) were generally weak. For hydrolases, ratios of specific C, N and P acquisition activities converged on 1 : 1 : 1 but across ecosystems, the ratio of C : P acquisition was inversely related to MAP and MAT while the ratio of C : N acquisition increased with MAP. Oxidative activities were more variable than hydrolytic activities and increased with soil pH. Our analyses indicate that the enzymatic potential for hydrolyzing the labile components of soil organic matter is tied to substrate availability, soil pH and the stoichiometry of microbial nutrient demand. The enzymatic potential for oxidizing the recalcitrant fractions of soil organic material, which is a proximate control on soil organic matter accumulation, is most strongly related to soil pH. These trends provide insight into the biogeochemical processes that create global patterns in ecological stoichiometry and organic matter storage.