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Recent studies show that a labile soil carbon (C) fraction determined with potassium permanganate (KMn[O.sub.4]) reflects the type of soil management. The present study combines the method for determining the active C (AC) pool with an alternative titration of the 0.02 m KMn[O.sub.4] solution with sodium oxalate ([Na.sub.2][C.sub.2]4) for routine laboratory analyses. Three long-term field experiments investigated: (i) different cropping systems and [sup.14]C-labelled organic amendments, (if) three different tillage systems, and (iii) the application of four different kinds of compost. The results showed the depletion of AC in the permanent bare-fallow system of the [sup.14]C-labelled field experiment. When calculating the ratio AC/total organic C (TOC), the depletion of the AC/TOC curve reflected a priming effect, in accord with previous work. We obtained significant positive correlations of AC with TOC, total nitrogen ([N.sub.t]), humic acid-C and remaining [sup.14]C-labelled material. The AC in the tillage systems experiment was significantly (Pc 0.05) different between all three tillage treatments at 0-10 cm depth, and the ratio AC/TOC also revealed a significant difference between minimum and conventional tillage treatments at 10-20 cm. For the compost field experiment, significant differences occurred between plots fertilised solely with N and plots receiving organic amendments. The AC/TOC ratio of the sewage sludge amendment was significantly lower than in all other systems. Correlations of AC with TOC for all samples of the different long-term field experiments revealed different behaviours in different soil types. The correlations of AC with [N.sub.t] showed higher coefficients than with TOC. The applied methodology has a potential for sensitive and reliable detections of differences in soil organic matter characteristics. Additional keywords: [sup.14]C label, compost, cropping systems, SOM, tillage systems, titration., Introduction Global storage of soil organic carbon (SOC) is estimated to be 1502 Pg C in the first metre of soil (Jobbagy and Jackson 2000), including active and more stable [...]

Some topsoil physical properties evolve unfavourably under continuous, no-till fanning. On the Pampa, loam soils under no-till sometimes have lower infiltration rates than those conventionally tilled; this is due to the occurrence of platy and massive structures. In this study, we aimed to identify the soil management practices that promote platy structure formation, and explain the soil physical behaviour linked to the thickness of platy structures in relation to infiltration rate, bulk density and shear strength. Six fields with different numbers of years under agriculture and diverse previous crops (maize or wheat-soybean double crop) were sampled, distinguishing within each field headlands (areas with higher traffic) and centre (lower traffic). Twenty samples were taken at random along a 200-m transect to characterise soil structure (platy, granular or massive) and the thickness of the platy structure. Principal component analysis revealed linkages between previous crop and location in each field and type of structure. ANOVA showed a significant (Pc 0.05) interaction of previous crop x location. The frequency and thickness of the platy structures were lower, and those of granular structures higher, under wheat--soybean double cropping and in the centre of the field. Greater thickness of the platy structure determined lower water infiltration rate (r=-0.337; P Additional keywords: infiltration rate, machinery traffic, no-till, shear strength, structural types., Introduction Physical properties are an important part of the evaluation of soil quality and health (Hussain et al. 1999). Soil structure is generally characterised by form, stability and resilience. Structural [...]

The large amounts of carbon (C) and nitrogen (N) sequestered as organic matter in soils have implications for global and national C and N balances and greenhouse gas emissions. Changes in soil management can affect the amount of C and N stored in soil. We investigated the change in land use from radiata pine plantation to ryegrass--white clover dairy pasture on the total C and N content of Taupo Pumice Soil. Samples were taken at three study sites (Atiamuri, Tokoroa and Wairakei) in North Island, New Zealand. Soils were cored to 60 cm depth and subsampled by soil horizon, and bulk density cores were taken from soil pits. A chronosequence of sites was obtained after conversion from pines to pasture. Long- term pastures (40-80 years) and mature pine plantations were included for further comparison. Regression analyses were completed after logarithmic transformation of the time data. The data were highly variable, but significant (P Additional keywords: deforestation, land use change, pasture chronosequence, soil carbon, soil N, soil storage., Introduction There is increased interest in the amounts of carbon (C) and nitrogen (N) stored in soils, not only because of the benefits of organic matter on soil nutrient dynamics [...]

Reduced carbon stock levels in Australian soil due to cropping provide a significant opportunity for carbon sequestration, and the recent initiative to consider soil carbon in domestic emissions trading requires a scientific assessment of soil carbon levels under a range of cropping soil management practices. Some of the previous research in southern and western New South Wales (NSW) showed that the rate of carbon decline in cropping soils is slowed under minimum tillage when the stubble is also retained. However, such comparison is rare in the NSW North-West Slopes and Plains region, particularly on the red soils (Chromosols) which are one of the major soil types in the region. We surveyed 50 dryland Chromosols, 72 dryland Vertosols, and 25 irrigated Vertosols on commercial farms across this region to examine the effects of conventional tillage, minimum tillage, and irrigation on total soil organic carbon. Samples of 0.1 m segments to 0.3 m depth were analysed for total organic carbon and other soil properties. Mid-infrared scans were used to predict the particulate, humus, and resistant soil organic carbon fractions. Bulk density was used to calculate total organic carbon stock for each segment, and equivalent soil mass (ESM) for 0-0.3 m. In Vertosols, for 0-0.3 m ESM, total organic carbon and particulate organic carbon were not different between management practices, whereas humic organic carbon and resistant organic carbon were consistently lower under conventional tillage. However, in 0-0.1 m, total organic carbon was greater under minimum tillage (15.2 Mg [ha.sup.-1]) than conventional tillage (11.9Mg [ha.sup.-1]) or irrigation (12.0Mg [ha.sup.- 1]), reflecting less soil surface disturbance under minimum tillage. In Chromosols, only total organic carbon was higher under minimum tillage than conventional tillage in the 0-0.3 m ESM (39.8 v. 33.5 Mg [ha.sup.-1]) and in 0-0.1 m (19.7 v. 16.9 Mg [ha.sup.-1]). The strong influences of rainfall, temperature, bulk density, texture, and management history on soil carbon stocks suggested that these environmental and management factors require further consideration when gauging soil carbon sequestration potential under current and novel tillage practices in key regional locations. Additional keywords: carbon accounting, conservation tillage, soil carbon sequestration., Received 25 January 2013, accepted 4 June 2013, published online 20 December 2013 Introduction Soil is a significant global carbon (C) reservoir (Lal 2004). Because C is the main constituent [...]

Organic matter controls aggregate stability in loam soils. Intensive farming can lead to a decrease in soil organic matter content. In areas where livestock have disappeared, the recycling of composted urban organic wastes on agricultural soils may represent a valuable source of organic matter for restoring soil organic matter content. The effects on the aggregate stability of a silt loam soil of three urban composts (a municipal solid waste compost, a co-compost of sewage sludge and green waste, and a biowaste compost) sampled at two different stages of maturity (immature and mature composts) were studied during laboratory incubations. The results were related to (i) compost organic matter biodegradability, biochemical fractions, and humic substance content, (ii) microbial activity evaluated through organic C mineralization and microbial and fungal biomass evolution, (iii) hot-water-extractable polysaccharides, and (iv) aggregate hydrophobicity as revealed by the water drop penetration time test. Both immature and mature composts increased aggregate stability via different mechanisms. After immature compost addition, the enhanced microbial activity mainly improved aggregate stability by increasing water repellency. The fungal biomass was particularly involved in aggregate stabilization. The municipal solid waste compost was more efficient at improving resistance to slaking, probably because of its larger labile organic pool that enhanced microbial activity. The addition of mature composts immediately improved aggregate stability with similar efficiency for all composts but to a lesser extent than improvements from immature composts. The observed increase of interparticular cohesion could be due to the inward diffusion of binding organic substances within the aggregates. Abbreviations: BW, biowaste compost; [BW.sub.i], immature biowaste compost; [BW.sub.m], mature biowaste compost; GWS, green waste and sludge compost; [GWS.sub.i]: immature green waste and sludge compost; [GWS.sub.m], mature green waste and sludge compost; HWPC, hot-water-extractable polysaccharide carbon; MSW, municipal solid waste compost; [MSW.sub.i], immature municipal solid waste compost; [MSW.sub.m], mature municipal solid waste compost; MWD, mean weight diameter; [MWD.sub.FW] mean weight diameter after fast wetting test; [MWD.sub.MB], mean weight diameter after mechanical breakdown test; [MWD.sub.SW], mean weight diameter after slow wetting test; TOC, total organic carbon; WDPT, water drop penetration time.

To meet economic and environmental demands for about 10 billion people by the mid-21st century, humanity, will be challenged to double food production from the Earth's soil and diminish adverse effects of soil management on the wider environment. To meet these challenges, an array of scientific approaches is being used to increase understanding of long-term soil trends and soil--environment interactions. One of these approaches, that of long-term soil experiments (LTSEs), provides direct observations of soil change and functioning across time scales of decades, data critical for biological, biogeochemical, and environmental assessments of sustainability; for predictions of soil productivity and soil--environment interactions; and for developing models at a wide range of scales. Although LTSEs take years to mature, are vulnerable to loss, and have yet to be comprehensively inventoried or networked, LTSEs address a number of contemporary issues and yield data of special significance to soil management. The objective of this study was to evaluate how LTSEs address three questions that fundamentally challenge modern society: how soils can sustain a doubling of food production in the coming decades, how soils interact with the global C cycle, and how soil management can establish greater control over nutrient cycling. Results demonstrate how LTSEs produce significant data and perspectives for all three questions. Results also suggest the need for a review of the state of our long-term soil-research base and the establishment of an efficiently run network of LTSEs aimed at soil-management sustainability and improving management control over C and nutrient cycling. Abbreviations: FACE, flee-air carbon dioxide experiment; IRRI, International Rice Research Institute; LTCCE, Long-term continuous cropping experiment; LTSE, long-term soil experiment; RSS, repeated soil survey; SFTS, space-for-time substitution; STSE, short-term soil experiment.

Erosion rates and annual soil loss tolerance (T) values in evaluations of soil management practices have served as focal points for soil quality (SQ) research and assessment programs for decades. Our objective is to enhance and extend current soil assessment efforts by presenting a framework for assessing the impact of soil management practices on soil function. The tool consists of three steps: indicator selection, indicator interpretation, and integration into an index. The tool's framework design allows researchers to continually update and refine the interpretations for many soils, climates, and land use practices. The tool was demonstrated using data from case studies in Georgia, Iowa, California, and the Pacific Northwest (WA, ID, OR). Using an expert system of decision rules as an indicator selection step successfully identified indicators for the minimum data set (MDS) in the case study data sets. In the indicator interpretation step, observed indicator data were transformed into unitless scores based on site-specific algorithmic relationships to soil function. The scored data resulted in scientifically defensible and statistically different treatment means in the four case studies. The efficacy of the indicator interpretation step was evaluated with stepwise regressions using scored and observed indicators as independent variables and endpoint data as iterative dependent variables. Scored indicators usually had coefficients of determination ([R.sup.2]) that were similar or greater than those of the observed indicator values. In some cases, the [R.sup.2] values for indicators and endpoint regressions were higher when examined for individual treatments rather than the entire data set. This study demonstrates significant progress toward development of a SQ assessment framework for adaptive soil resource management or monitoring that is transferable to a variety of climates, soil types, and soil management systems.

Soil management systems affect soil porosity and pore sizes, changing soil hydraulic properties by loosening or by compacting different soil layers. Changes in porosity and pore-size distribution following cultivation were studied in six Ustolls and two Usterts of the prairie in the Upper Missouri River Basin. Soil pores were morphologically described. Water infiltration was measured at 0.03- and 0.06-m tensions. Soil bulk density and moisture retention at 1-m tension were determined in undisturbed and in remolded soil cores. In Ustolls, cultivation decreased soil porosity and pore sizes. Steady-state water infiltration rates were higher in grasslands than in cultivated soils. In no-till and till systems, both very fine macroporosity and microporosity were reduced when compared with grasslands. No-tillage relative to tillage increased soil porosity between the 0.05- and 0.30-m depth. More very fine tubular pores were present in no-till than in tilled Ustolls, indicating increased biological activity in pore formation. In Usterts, total pore space, quantity, shape, and size of macropores, water infiltration under tension, and moisture retention at 1-m tension did not show significant changes related to different management systems.

Soil survey information combined with exploratory simulation modeling was used to define indicators for sustainable land management. In one soil series in the Netherlands (the genoform), three different phenoforms were formed as a result of different management practices. Locations were identified using a soil map and interviews with farmers. Organic matter, bulk densities, and porosities were significantly different for the three phenoforms: biodynamic management (Bio), conventional management (Conv), and permanent grassland (Perm). By applying a dynamic simulation model for water movement, crop growth and N dynamics, the three phenoforms were analyzed in terms of sustainability indicators by defining four scenarios based on productivity and N leaching to the groundwater: (i) potential production, (ii) water-limited production, (iii) current management, and (iv) the environmental scenario. The latter was divided into EnvA: never exceeding the N-leaching threshold of 11.3 mg [L.sup.-1]; EnvB: exceedance occurring in one out of 30 yr; and EnvC: exceedance occurring in three out of 30 yr. Biodynamic management obtained the lowest yield under current management, while yields for Perm were highest. EnvA could not be reached for Perm as a result of high mineralization rates. Obtainable yields for scenarios EnvA, EnvB, and EnvC differed substantially, illustrating the importance of selecting 'acceptable' risks in environmental regulation. The presented methodology demonstrates the importance of pedological input in sustainability studies.

An analysis of the influence of long-term crop rotation and management of dispersible clay in two different types of soil in Saskatchewan reveals cultivated soil to be move dispersive than grassland soil. Aggregate stability is not the main factor affecting water-dispersible clay in many soil textural classes, but may be an important source of difference in a single series.

Limited irrigation and tillage treatments have no influence on the water storing capacity of the soil during fallow after wheat cultivation. Difference of yield between grain and straw is minimum due to a relatively small difference of soil water content. Production of winter wheat and grain sorghum is enhanced using tillage methods which retain the residues of these crops on the soil surface.

Laboratory investigations of the influence of ammonium lignosulfonate (LS), thiophosphoric triamide (NBPT) and phenylphosphorodiamide (PPD) on NH3 depletion from area fertilizer revealed no major differences in NH3 depletions between surface-applied and banded protocols of solid fertilizer. LS was poorer in lowering NH3 depletion than NBPT and PPD. Major differences between NBPT and PPD were absent.

An analysis of plant productivity and N consumption of successive crops of corn involved the establishment of the influence of long-term inorganic and organic N soil management, animal and plant legume organic soil changes and lowering inorganic N rates in the presence of organic changes. Plant productivity was preserved by pea vine residue or poultry manure at the fourth crop at a time when inorganic N applications was zero.

The conservation tillage methods and herbicides used to control weed reduced soil losses on sloping soybean fields. Runoff and erosion on six small watersheds where corn and soybean were farmed in rotation for six years were determined to assess soil loss in these new settings. The production is confined to flat lands, when traditional tillage and mechanical cultivation are used to control weed.

The dentrification dissimilatory NO3- reduction and nitrogen mineralization immobilization in a Brookston clay loan was studied to establish the effect of incorporating hairy vetch (HV, Vicia villosa), reed canarygrass (RCG, Phalaris arundinacea L.), annual ryegrass (AGR, Lolium multiflorum), red clover (RC, Trifolium pratense L.) and corn (Zea mays L.) residues. From the third to the fifth day of the aerobic inerbation, mineralization took place during the treatment of HV. During the anaerobic phase, nitrite was accumulated in all cases.

Differences in crop and fertilizer management are known to influence P retention by soils. An experiment was conducted to study the effect of soil characteristics and management practices on P sorptoin behavior of the highland plateau soils of Ethiopia. Surface samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers' fields, research station farms, and from non-cultivated-non-fertilized areas. Phosphorus sorption data were obtained by equilibrating 3-g soil samples in 30 mL of 0.01 M Ca[Cl.sub.2] containing various amounts of [KH.sub.2][PO.sub.4]. Inorganic P fractions were determined by the Hedley P fractionation scheme. There was little variation in P sorption among Vertisol samples of alluvial origin as a result of cultivation-fertilization practices. For soils of volcanic origin (Vertisol2 and Andisols), and the Alfisol, samples collected from farmers' fields sorbed more P than the non-cultivated and research station samples. Least amounts of applied P sorbed by the non-cultivated Andisol samples reflect the relatively large amounts of resin extractable P initially present in these soils and demonstrate that labile P initially present in the soil can influence subsequent P sorption. Stepwise regression analysis of the P sorption data showed that resin P accounts for 81% of the variation in P sorption at 0.2 mg P [L.sup.-1] in solution. The highest amount of P was sorbed by samples collected from farmers' fields and was mainly due to the practice of continuous cropping with minimal P fertilization, which depletes labile P, and therefore requires higher levels of P fertilization for optimum crop yield.

Soil erosion is a major constraint to the sustainability of sloping-land vegetable systems. Little information is available on the effectiveness of soil conservation measures under sloping intensified vegetable systems on volcanic ash-derived soils. We hypothesized that contouring, strip cropping, and high-value contour hedgerows -- asparagus (Asparagus officinalis L.), pineapple [Ananas comosus (L.) Merr.], pigeonpea [Cajanus cajan (L.) Huth], and lemongrass [Cymbopogon flexuosus (Nees ex Steudel) J. F. Watson] -- reduce soil loss compared with the farmer's traditional practice of up-and-down cultivation on sloping lands. A field experiment tested these soil conservation technologies from 1995 to 1998 in a completely randomized block design on a 42% natural slope on a clayey, halloysitic, isothermic, Typic Kandiudox. The greatest annual soil loss (65.3 t [ha.sup.-1]) was in the up-and-down system and comparative values were 37.8 t [ha.sup.-1] for contouring, 43.7 t [ha.sup.-1] for strip cropping, and 45.4 t [ha.sup.-1] for highvalue contour hedgerows. Three rain events alone caused 47% of the total soil loss. All erosion-runoff plots showed large differences in soil properties and crop yields between the upper and the lower slope. Crop yields downslope were greater by 40% for tomato (Lycopersicon esculentum Miller), 36% for corn (Zea mays L.), and 78% for cabbage (Brassica oleracea var. capitata L.) than for upslope. In the contour hedgerow treatment, rapid terrace development changed soil properties, and crop yields for the bottom portions of bioterraces were greater by 121% for corn and 50% for tomato than yields of top portions.