Changes In Agricultural Management Practices Research Articles

Crop management strategies shape the shared temporal dynamics of soil food web structure and functioning

In recent decades, there has been growing interest in exploring the soil biota, highlighting the significance of soil organisms' networks in soil functioning. Here, we use a modeling approach to investigate how changes in cropping practices influence the soil food web dynamics and it relates to that of soil functioning. In an experimental trial, we tested for change in topsoil food webs after shift from conventional to alternative practices (changes in tillage intensity, amount of residues returned and N fertilization rate). Samplings were made in 16 plots of a randomized complete block design during spring of year 0, 2 and 4 after the onset of the trial. Microorganisms, microfauna, mesofauna and macrofauna were sampled, identified and grouped into trophic groups. We built a general soil food web describing plausible carbon flows between these trophic groups and computed several network indices. At the same dates, soil functions linked to C and N dynamics were measured from soil samples. We used a COSTATIS analysis to investigate relationships between temporal sequences of soil functions and soil food web indices. Significant interactive effects of the date and of agricultural systems were found on the mean and the maximum trophic level, the bacterial-to-fungal path ratio, the total biomass and the way biomass accumulates across trophic levels, the number of trophic groups and the functional redundancy in trophic groups. Similarly, organic matter transformations and enzymatic activities showed differences across date and agricultural systems. Results show that temporal changes in soil food web structure and in soil processes related to N and C cycling co-vary following changes in agricultural management practices. Management practices related to tillage exerted stronger effects on soil food web functioning than those related to the export of crop residues or reduction in mineral N fertiliser. For instance, reduced tillage lead to more complex food webs, with increased C and N mineralization in the upper soil layer (0–5 cm), in which most of the residues accumulate. Our results provide insights on soil food webs temporal dynamics, even within a restricted panel of agricultural practices. Our results suggest that changes in agricultural practices influence feedbacks between organisms and the functions they perform, so that a temporal co-structure can be observed in the studied site. Such work could help better understand the mechanisms of resistance or ecological debt during agroecological transition, which could limit or delay expected Nature-based solutions.

Farmers Feel the Climate Change: Variety Choice as an Adaptation Strategy of European Potato Farmers

Effects associated with a changing climate could severely threaten potato production in Europe. Hence, farmers need to take up adaptation measures to safeguard agricultural production. Collecting data from 553 farmers from 22 different European countries, our survey evaluates European potato farmers’ perceptions regarding the influence of climate change on local potato production, and their willingness to implement adaptation strategies. An overwhelming majority of survey respondents had already experienced the effects of climatic changes on their potato production. Specifically, drought and heat were identified as the most significant threats. The planting of an adapted variety was the preferred adaptation strategy, while farmers were also willing to take up changes in agricultural management practices. Survey respondents predominantly considered yield stability as the most important characteristic of an adapted variety, closely followed by heat tolerance, disease resistance, drought tolerance, and yield potential. When choosing a variety, the personal experience of the survey respondents as well as the experience of their peers were identified as the most important sources of information. Our survey gives valuable insights into the challenges European potato farmers are facing in times of climate change. Supplying farmers with better-adapted varieties would be a well-targeted and well-accepted measure to advance climate change adaptation.

Early effects of conservation agriculture on soil organic carbon dynamics of Mollisols in Cambodia

AbstractCambodia has faced drastic agrarian changes over the last twenty years with a rapid and massive transformation of the uplands from forest into arable land. Soil quality depletion is one of the main drivers of the resulting decline in crop productivity and increasing production costs in the uplands of Battambang province. The objective of the study was to assess the early effects of conventional plough‐based (20 cm) management (CT) and two conservation agriculture‐based (CA) cropping systems (the use of a single—CAS vs. multiple cover crop species—CAM) on a maize monocropping system using three soil organic carbon (SOC) fractions on Mollisols in Battambang province. SOC content, permanganate oxidizable carbon (POXC) and soil CO2 basal respiration through SituResp® were recorded at a depth of 0–10 cm. Twelve sampling periods were used over the growth period of the cover crops and during the maize cycle. POXC and SituResp® were highly sensitive to management practices with, across the 12 sampling periods, higher values (p < .05) under CA than CT, with an average increase of 6% and from 20% to 23%, respectively. No difference was observed in SOC content between the practices in our sampling periods. Seasonal variations were observed in both POXC and SituResp®. POXC underwent larger fluctuations following critical weather events than SituResp®. This study showed that POXC and SituResp® were rapidly sensitive to changes in agricultural management practices. POXC and SituResp® are largely influenced by seasonality and could help clarify the impact of weather patterns on soil C dynamics.

Historical and projected impacts of climate change and technology on soybean yield in China

CONTEXTIncreasing soybean yield is essential for China. In order to secure the desire soybean yield gains, it is important to understand how changes in climate and technology impact soybean yield. OBJECTIVEFirst, we used historical climate and specific technology data assessed the impact of historical climate and technology on soybean yield in China. Second, combined with the historical yield linear trends, we projected future soybean yield under climate change and technology improvement. METHODSWe collected the historical climate data (daily maximum and minimum temperatures, precipitation, and solar radiation) and actual crop data (soybean yield and agricultural management practices: sowing date, total agricultural machinery, effective irrigation area, pesticide application amount, and rural labor force) of 1312 soybean-growing counties in China from 1990 to 2017. Besides, we calibrated and validated the vegetative and reproductive stages, and the yield formation process genetic parameters of soybean of different maturity groups in DSSAT-CROPGRO-Soybean model by a five-year cycle based on soybean field experiment data. We defined agricultural management practices and genetic parameters as technology, and used Bayesian methods to conduct an impact assessment of historical climate and technology changes on soybean yield. We also projected soybean yield from 2021 to 2100 under climate change and different cases of technology improvement. RESULTS AND CONCLUSIONSFrom 1990 to 2017, more than 90% of the study counties showed an increase in soybean yield, although the yield increase slowed down after 2010. Agricultural management practices and genetic parameters changes increased soybean yield by 16% (−24 to 50%) and 6% (−14 to 24%), respectively, while climate change decreased soybean yield by 1% (−14 to 18%). The positive impacts of agricultural management practices were mainly attributed to pesticide application amount and total agricultural machinery. With changes in agricultural management practices alone, soybean yield showed a plateau or even a decrease after 2010. If the technology remains at the level it was in 2010s, soybean yield would decrease in the future in 49% of the counties. SIGNIFICANCEBased on climate, soybean yield, specific agricultural management practices and genetic parameters data, we quantified the impacts of historical climate and technology on soybean yield in China. Besides, we projected future soybean yield under climate change and different cases of technology improvement, and discussed possible solutions for future increasing soybean yield. This work has practical significance for understanding climate and technology impacts on soybean yield, and implementing countermeasures to address future climate change and increase yield.

Impacts of switching tillage to no-tillage and vice versa on soil structure, enzyme activities and prokaryotic community profiles in Argentinean semi-arid soils.

The effects of tillage on soil structure, physiology and microbiota structure were studied in a long-term field experiment, with side-to-side plots, established to compare effects of conventional tillage (CT) vs no-till (NT) agriculture. After 27 years, part of the field under CT was switched to NT and vice versa. Soil texture, soil enzymatic profiles and the prokaryotic community structure (16S rRNA genes amplicon sequencing) were analyzed at two soil depths (0-5 and 5-10cm) in samples taken 6, 18 and 30 months after switching tillage practices. Soil enzymatic activities were higher in NT than CT, and enzymatic profiles responded to the changes much earlier than the overall prokaryotic community structure. Beta diversity measurements of the prokaryotic community indicated that the levels of stratification observed in long-term NT soils were already recovered in the new NT soils 30 months after switching from CT to NT. Bacteria and Archaea OTUs that responded to NT were associated with coarse soil fraction, soil organic carbon and C cycle enzymes, while CT responders were related to fine soil fractions and S cycle enzymes. This study showed the potential of managing the soil prokaryotic community and soil health through changes in agricultural management practices.

A multidimensional perspective to farmers’ decision making determines the adaptation of the farming community

Agricultural adaptation to climate change includes changes in agricultural management practices which will be quite effective in reducing the probability of crop failure and improving the socio economic condition of farmers. Knowledge about the decision making process of farmers can help in identifying the determinants of adaptation to them. It is very important to model the farmers' behaviour and decision making process to answer the reasons for farmers' suicides and inequalities arising out within the farmers belonging to same group. Our study identifies the factors responsible for increasing inequalities, crop failure and differential decision making capabilities of farmers by surveying 400 farmers in eighteen villages of Maharashtra, India. We analysed how combination of various factors such as social, economic, infrastructural and institutional affect the decision making process of farmers which brings out the novelty of the present work that can be replicated across a spectrum of such studies. Further, different adaptation options were categorized into the most and least preferred adaptive strategies by considering the farmers' perception. Our work has also identified which particular factor i.e. climatic, institutional, infrastructural or socio-economic is the major challenge towards the adaptation of farmers. The study has followed logit model in investigating the farmers' adaptation to multiple stressors. The study has also addressed the on-going argument regarding the scale of policy formulation i.e., whether policy formulation should take place at micro scale (Decentralization) or at larger region (State/National) level. Findings revealed that farmers perceive climate variability in terms of monsoon and temperature variability and respond as per their indigenous knowledge and experience. Model results revealed that institutional, social and climatic factors should be the focus point of government for improving the adaptation profile of farmers.

Riparian wetland rehabilitation and beaver re-colonization impacts on hydrological processes and water quality in a lowland agricultural catchment

Quantifying the catchment water balance and the characterization of its water quality changes are effective tools for establishing the response of catchments to shifting land management practices. Here we assess long-term hydrological partitioning and stream water chemistry over a 30-year period in a rural mixed land use catchment in northern Germany undergoing riparian wetlands and widespread re-colonization by beavers (Castor fiber) along the river network. We used long-term spatially distributed stream discharge, groundwater levels and surface water quality data with a simple monthly water balance model, changes in the variability in discharge measurements, and statistical analysis of spatio-temporal changes in stream water quality to assess long-term changes. Water balance estimates indicated high proportions of evapotranspiration loss (~90% of total precipitation) and relatively low groundwater recharge (<5% of total precipitation) prior to riparian rehabilitation in 2000. Increasing groundwater levels from 2000 to 2017 and the relatively linear nature of the catchment storage – discharge relationship, indicate a gradual increase in groundwater recharge (buts still <10% of total precipitation). Wetland rehabilitation, greatly enhanced by increasing beaver populations, resulted in longer water transit times in the stream network, less linear storage-discharge relationship and a loss of daily stream variability, increased DOC concentrations, isotopic evaporative enrichment downstream, and moderated stream temperatures. There was limited long-term water quality improvements from wetland rehabilitation on either nitrate or total phosphorus concentrations, with unchanged seasonal summer and winter peak concentrations for phosphorus and nitrate, respectively. This likely reflects the long-term legacy of fertilizer use on nutrient reservoirs in the catchment's soils, aquifers, and stream network. These long-term changes in hydrology and stream chemistry resulting from riparian rehabilitation and changes in agricultural management practices provide invaluable insights into catchment functioning and an evidence base for future planning in relation to long-term climatic changes.

Challenges of Reducing Phosphorus Based Water Eutrophication in the Agricultural Landscapes of Northwest Europe

In this paper, we outline several recent insights for the priorities and challenges for future research for reducing phosphorus (P) based water eutrophication in the agricultural landscapes of Northwest Europe. We highlight that new research efforts best be focused on headwater catchments as they are a key influence on the initial chemistry of the larger river catchments, and here many management interventions are most effectively made. We emphasize the lack of understanding on how climate change will impact on P losses from agricultural landscapes. Particularly, the capability to disentangle current and future trends in P fluxes, due to climate change itself, from climate driven changes in agricultural management practices and P inputs. Knowing that, future climatic change trajectories for Western Europe will accelerate the release of the most bioavailable soil P. We stress the ambiguities created by the large varieties of sources and storage/transfer processes involved in P emissions in landscapes and the need to develop specific data treatment methods or tracers able to circumvent them, thereby helping catchment managers to identify the ultimate P sources that most contribute to diffuse P emissions. We point out that soil and aqueous P exist not only in various chemical forms, but also in range of less considered physical forms e. g., dissolved, nanoparticulate, colloidal and other particulates, all affected differently by climate as well as other environmental factors, and require bespoke mitigation measures. We support increased high resolution monitoring of headwater catchments, to not only help verify the effectiveness of catchments mitigation strategies, but also add data to further develop new water quality models (e.g., those include Fe-P interactions) which can deal with climate and land use change effects within an uncertainty framework. We finally conclude that there is a crucial need for more integrative research efforts to deal with our incomplete understanding of the mechanisms and processes associated with the identification of critical source areas, P mobilization, delivery and biogeochemical processing, as otherwise even highintensity and high-resolution research efforts will only reveal an incomplete picture of the full global impact of the terrestrial derived P on downstream aquatic and marine ecosystems.

Legacy nitrogen may prevent achievement of water quality goals in the Gulf of Mexico.

In August 2017, the Gulf of Mexico's hypoxic zone was declared to be the largest ever measured. It has been estimated that a 60% decrease in watershed nitrogen (N) loading may be necessary to adequately reduce eutrophication in the Gulf. However, to date there has been no rigorous assessment of the effect of N legacies on achieving water quality goals. In this study, we show that even if agricultural N use became 100% efficient, it would take decades to meet target N loads due to legacy N within the Mississippi River basin. Our results suggest that both long-term commitment and large-scale changes in agricultural management practices will be necessary to decrease Mississippi N loads and to meet current goals for reducing the size of the Gulf hypoxic zone.

Monitoring microbial functional and structural diversity for management of disease-suppressive soils

The activities of the soil microbiota are essential to the long-term sustainability of agricultural systems, through their influences on biological, chemical and physical processes, which drive essential ecosystem services. Moreover, changes in microbial communities are considered as precursors to changes in the health and viability of the soil environment, due to their responses to changes in agricultural management practices. Therefore, measurements of soil microbial activity and diversity are ideal indicators for monitoring soil status and the efficacy of soil management. However, due to the vast taxonomic diversity of soil microorganisms, analysis of microbial diversity is often problematic, time consuming and costly. Two banana experiments were established in far north Queensland, Australia, under different nutrient and groundcover management practices, to understand the dynamic changes in soil microbial communities and their effectiveness to sustain ecosystem services, such as organic matter decomposition and disease suppression. Using a functional approach, soil biological communities were analysed using trophic analysis of soil nematode communities, community level physiological profiles and enzyme activity assays. A reduction in nitrogen fertiliser inputs was related to a greater number of fungivorous nematodes which was also linked to greater suppression of Fusarium oxysporum f. sp. cubense using a novel soil-baiting bioassay. Furthermore, community-level physiological profiles enabled differentiation of soils over time demonstrating a shift in soil microbial functional diversity. The results highlight how soil management can drive differences in soil microbial activity and diversity to improve soil functions in banana production.

Data synthesis of carbon distribution in particle size fractions of tropical soils: Implications for soil carbon storage potential in croplands

Organic carbon saturation in soils refers to the theoretical maximum soil organic carbon (SOC) that can be associated with and stabilized on fine silt plus clay particles (F<20μm). We reviewed the literature dealing with SOC distribution between soil fractions to evaluate carbon saturation for tropical soils and estimate the C storage potential of cropland.We collected 258 data points on SOC distribution between soil fractions in tropical soils from 84 sites in 27 countries. We used boundary line analysis to estimate the maximum stabilized SOC depending on soil group, clay type and land use. SOC storage potential was calculated as the SOC saturation deficit, the difference between the actual SOC content and the maximum stabilized SOC content.We found that the maximum SOC in the fine fraction of tropical soils (53gCkg−1 fine fraction) was lower than previous assessments of global SOC storage scale based mainly on temperate soils. The F<20μm fractions were closer to SOC saturation in forest soils than in croplands. The cropland had a higher soil C storage potential, but changing agricultural management practices did not fill the deficit that is calculated using the whole dataset. The deficit was much lower when it was estimated with grassland or cropland data only: this provides a more realistic estimate for SOC storage potential for croplands.The SOC content in the coarser fraction (F>50μm) did not depend on soil texture and significantly contributed to the total SOC, especially in sandy soils (41.3%). This is affected by changes in agricultural management practices. We concluded that, although the aim of increasing SOC stabilization originally arose from climate change mitigation strategies, it must now be more viewed as being more relevant to food security and local adaptation to climate change.

Substantial Underestimation of Post-Harvest Burning Emissions in the North China Plain Revealed by Multi-Species Space Observations.

The large-scale burning of crop residues in the North China Plain (NCP), one of the most densely populated world regions, was recently recognized to cause severe air pollution and harmful health effects. A reliable quantification of the magnitude of these fires is needed to assess regional air quality. Here, we use an eight-year record (2005–2012) of formaldehyde measurements from space to constrain the emissions of volatile organic compounds (VOCs) in this region. Using inverse modelling, we derive that satellite-based post-harvest burning fluxes are, on average, at least a factor of 2 higher than state-of-the-art bottom-up statistical estimates, although with significant interannual variability. Crop burning is calculated to cause important increases in surface ozone (+7%) and fine aerosol concentrations (+18%) in the North China Plain in June. The impact of crop fires is also found in satellite observations of other species, glyoxal, nitrogen dioxide and methanol, and we show that those measurements validate the magnitude of the top-down fluxes. Our study indicates that the top-down crop burning fluxes of VOCs in June exceed by almost a factor of 2 the combined emissions from other anthropogenic activities in this region, underscoring the need for targeted actions towards changes in agricultural management practices.

Application of the SWAT model to assess the impact of changes in agricultural management practices on water quality

An excessive use of nitrogen in agricultural regions leads to nitrate pollution of surface and groundwater systems. The Alegria River watershed (Basque Country, northern Spain) is an agricultural area dominated by a Quaternary shallow aquifer that has suffered nitrate-related problems since the 1990s. Our objective was to use the SWAT hydrological water quality model for long-term backward simulation (1990–2011) considering main changes in management practices to determine their impact on water quality. Hydrology, crop yield, nitrogen losses and soil nitrogen budgets were simulated satisfactorily. Nitrogen budgets indicated that annual N inputs exceed outputs (which consider main N loss pathways), resulting in mean N surpluses of 114 and 65 kg ha-1 year-1 in the periods 1990–1999 and 2000–2011, respectively. In the long-term, trends in N surplus generally follow those of fertilization input, which directly affect groundwater nitrate concentration. The characteristics of the aquifer and non-point source pollution have enabled us to properly simulate the historical trends in N concentration in the Vitoria-Gasteiz aquifer.Editor Z.W. Kundzewicz; Guest editor V. Krysanova

Agricultural adaptation strategies to climate change impacts in Africa: a review

Climate change is expected to intensify existing problems and create new combinations of risks, particularly in Africa. The situation is made worst due to factor such as widespread poverty, over dependence on rain fed agriculture, inequitable land distribution, limited access to capital and technology, inadequate public infrastructure, such as roads, long term weather forecasts and inadequate research and extension. By lessening the severity of key damages to the agricultural sector, adaptation is the key defensive measure. Adaptation to climate change involves changes in agricultural management practices in response to changes in climate conditions. This paper reviews agricultural adaptation strategies employed by farmers in various countries in Africa in cushioning the effects of climate change. The common agricultural adaptation strategies used by farmers were the use of drought resistant varieties of crops, crop diversification, changes in cropping pattern and calendar of planting, conserving soil moisture through appropriate tillage methods, improving irrigation efficiency, and afforestation and agro-forestry. The paper concluded that improving and strengthening human capital through education, outreach programmes, extension services at all levels will improve capacity to adapt to climate change impact. DOI: http://dx.doi.org/10.3329/bjar.v39i3.21984 Bangladesh J. Agril. Res. 39(3): 407-418, September 2014

Carbon dioxide emissions from tillage of two long-term no-till Canadian prairie soils

Agricultural soils under long-term zero tillage (no-till) management have been well known to sequester atmospheric carbon (C) in soil organic matter as well as to reduce emissions of major greenhouse gases. This fact aided the development of the present C offset market around the world and is the basis for no tillage or conservation tillage agriculture as a potential low cost means of reducing greenhouse gas (GHG) emissions. The province of Alberta, Canada currently has C offset protocols under which companies that fail to achieve targeted emission reduction can purchase C credits from agricultural farms that have changed tillage management practices. Our study aimed at quantifying the major GHG carbon dioxide (CO2) emissions from two major agricultural soil types in Western Canada (i.e., Black Chernozem and Gray Luvisol) managed under long-term (∼30 years) no-till after tillage reversal. We also studied the influences of soil temperature and soil moisture, nitrogen (N) fertilization (i.e., no N vs. 100kgNha−1) and inherent soil fertility on the magnitude of tillage reversal impact on soil CO2 emissions. Our study revealed that the CO2 emissions were higher after tillage reversal irrespective of N fertilizer applications, soil types and soil physical environment. Comparative study between historic soil C sequestration after the adoption of long-term no-till and the GHG emissions in the form of CO2 fluxes after tillage reversal on these study plots showed that the short-term rates of C emissions after tillage reversal were higher than the long-term rates of C sequestration. However, since the time scales for comparing the sequestration and emission rates were so different, these results are expected and reasonable. These results, however, indicate that increased soil C storage resulting from changes in agricultural management practices are reversible and that the potential for C sequestration is dependent on the long-term trends of management practices.

Identifying soil organic carbon fractions sensitive to agricultural management practices

Agricultural management practices play a major role in the process of SOC sequestration. However, the large background of stable carbon (C) already present in the soil and the long period of time usually required to observe changes in soil organic carbon (SOC) stocks have increased the necessity to identify soil C fractions with a fast response to changes in agricultural management practices. Consequently, we quantified the response of total SOC, permanganate oxidizable organic carbon (POxC), particulate organic carbon (POC) and the carbon concentration of water-stable macroaggregates, microaggregates within macroaggregates and the silt-plus clay-sized fraction (M-C, mM-C, s+cM-C, respectively) to changes in management. We chose a long-term tillage and N fertilization field experiment (18 years) located in NE Spain. In the first 5cm depth under no-tillage (NT) compared with conventional tillage (CT), the POxC fraction and total SOC increased similarly (about 59%). However, other C pools studied (i.e., M-C, M-POxC, mM-C, POC and s+cM-C) had lower increases with values ranging from 17% to 31%. For the 5–20 and 20–40cm soil depths, the POC was the most sensitive fraction to tillage with 46% and 54% decrease when NT was compared to CT, respectively. Likewise, the POC fraction presented the highest response to N fertilization in the three depths studied (i.e., 0–5, 5–20 and 20–40cm). The mM-C and s+cM-C fractions presented the lowest sensitivity to changes in tillage and N fertilization management. Our results showed that the POC fraction had the greatest sensitivity to changes in agricultural management practices, proving its ability as an early indicator of optimized practices to sequester C in soil.

Predictability of soil succession patterns under different agricultural land use practices: Continual conventional cultivation versus transformation to organic cultivation or fallow periods

Abstract Changes in agricultural management practices create conditions that directly or indirectly promote the onset of secondary succession processes in the soil. Previous research has demonstrated that the succession of temperate forests follows the Markov principle, which states that the next state of a process depends only on the preceding state; hence, we set out to test this principle for soils subjected to different land uses over a 2 year period. Specifically, (1) continued conventional cultivation (i.e. the monoculture of shell beans, Phaseolus vulgaris L., with chemical fertilisers); (2) transformation of land-use from conventional cultivation to organic cultivation (shell beans fertilised with manure); and (3) transformation of land-use to a fallow state. The soil was sampled three times at specific shell bean growth stages (June, the seedling stage; August, mid-growth; October, one month after harvest) in both years, with various chemical and biochemical soil profiles being conducted (including carbon, nitrogen and phosphorus levels, and enzymatic activity). Correlations among successive soil chemical and biochemical profiles were stronger (two successive events: June and August, August and October) in the first year compared to the second year (one successive event: August and October) for the organic plots. For soils in which conventional land management was continued, significant correlation was only detected for one successive profile (August–October) in both years, whereas no significant correlation was obtained for any successive profiles in the fallow plots. Therefore, the Markov principle only holds for the entire cultivation period under certain conditions for bean crops; specifically, initial conventional cultivation followed by transformation to organic cultivation. In the case of continued conventional monoculture, the Markov principle is partially supported. In contrast, fallow plots did not follow any predictable pattern of changes in soil chemical and biochemical profiles. In conclusion, agricultural management causes soil succession processes to be predictable, due to the environmental homogeneity induced by manure and/or the limited plant effect, rather than natural processes.

A Comparative Analysis of Phenological Curves for Major Crops in Kansas

The goal of this research was to conduct an initial investigation into whether a time-series NDVI reference curve library for crops over a growing season for one year could be used to map crops for a different year. Time-series NDVI libraries of curves for 2001 and 2005 were investigated to ascertain whether or not the 2001 dataset could be used to map crops for 2005. The 2005 16-day composite MODIS 250 m NDVI data were used to extract NDVI values from 1,615 field sites representing alfalfa, corn, sorghum, soybeans, and winter wheat. A k-means cluster analysis of NDVI values from the field sites was performed to identify validation sites with time-series NDVI spectral profiles characteristic of the major crop types grown in Kansas. After completing the field site refinement process, there were 1,254 field sites retained for further analysis, referred to as "final" field sites. The methods employed to evaluate whether the MODIS-based NDVI profiles for major crops in Kansas are stable from year-to-year involved both graphical and statistical analyses. First, the time-series NDVI values for 2005 from the final field sites were aggregated by crop type and the crop NDVI profiles were then visually assessed and compared to the profiles of 2001 to ascertain if each crop's unique phenological pattern was consistent between the two years. Second, separability within each crop class in the time-series NDVI data between 2001 and 2005 was investigated numerically using the Jeffries-Matusita (JM) distance statistic. The results seem to suggest that time-series NDVI response curves for crops over a growing period for one year of valid ground reference data may be useful for mapping crops for a different year when minor temporal shifts in the NDVI values (resulting from inter-annual climate variations or changes in agricultural management practices) are taken into account.

Protection of organic carbon in soil microaggregates via restructuring of aggregate porosity and filling of pores with accumulating organic matter

We examined relationships between the pore structure of microaggregates and the protection of organic matter (OM) within that structure. By using ultra-small angle X-ray scattering (USAXS) before and after combustion of microaggregates at 350 °C, we took advantage of differences in X-ray scattering contrast among soil minerals, OM, and air to evaluate the distribution of the total- and OM-filled porosity within microaggregates (53–250 μm in diameter). Systematic changes in microaggregate structure were observed for long-term field manipulations of land use (a chronosequence of tallgrass prairie restorations) and agricultural management (conventional tillage versus no-till at two levels of nitrogen fertilization). Our results imply that OM preservation arose from the evolution of the architectural system of microaggregates during their formation and stabilization. Soils and treatments with increasing OM in microaggregates were associated with encapsulation of colloidal OM by minerals, thereby creating protected OM-filled pores at the submicron scale within the microaggregate structure. For example, in the prairie chronosequence, microaggregates from the cultivated soil had the lowest concentration of OM, but 75% of the OM that had survived cultivation was in OM-filled pores. Following restoration, the concentration of OM in microaggregates increased rapidly, but the proportion of OM in OM-filled pores declined initially and then increased over time until 90% of the OM was in OM-filled pores. OM totally encapsulated within the pore structure can create spatial and kinetic constraints on microbial access to and degradation of OM. Encapsulation of OM increases the capacity for its protection relative to sorption on mineral surfaces, and comparison of its extent among treatments suggests important feedback loops. The use of USAXS, which has not previously been applied to the study of soil aggregate structures and the distribution of OM within those structures, provided new information on the mechanisms of OM protection in soil microaggregates, and insights relevant to strategies for enhancing carbon-sequestration in soil through changes in agricultural management practices and land use.

An approach for estimating soil carbon using the National Nutrient Loss Database.

Agricultural lands have the potential to contribute to greenhouse gas mitigation by sequestering organic carbon within the soil. Credible and consistent estimates will be necessary to design programs and policies to encourage management practices that increase carbon sequestration. Because a nationwide survey of soil carbon by the wide range of natural resources and management conditions of the United States is prohibitively expensive, a simulation modeling approach must be used. The National Nutrient Loss Database (NNLD) is a modeling and database system designed and built jointly by the USDA- Natural Resources Conservation Service (NRCS) and Texas A&M University to provide science-based inferences on environmental impacts from changes in agricultural management practices and programs at the regional and national level. Currently, the NNLD simulates 16 crops and covers approximately 1.35 x 10(8) ha. For estimating soil carbon sequestration, the database will be populated with approximately 1.5 x 10(6) field-level model runs using the EPIC (Environmental Policy Impact Calculator) model, which includes newly incorporated carbon equations consistent with those in the Century model. Each run will represent a unique situation defined by state, crop, climate, soil, irrigation type, conservation practice, tillage system, and nutrient management treatment (nutrient rate, application frequency, application timing, and manure category). Results are to be assigned to specific National Resource Inventory points (NRI) to simulate regional and national baselines. In this article we present the modeling approach and discuss the strengths and limitations.