A range of methods and applications are in use to determine soil particle size distribution. Due to the differences in measurement technology, the analytical results may deviate more or less from each other, which has implications for the matching with historical soil databases. There is a need for studies to critically evaluate their results, both concerning subsample variabilities and compatibilities. In the present study the more recent integral suspension pressure (ISP) and laser diffraction (LDM) methods were compared with the reference sieve and pipette (SPM) method. Samples from topsoil and subsoil of four agricultural soils with sandy clay loam to clay textures were analyzed. A protocol, comparing alternative pre-sievings at the meshes 0.063 (ps0.063), 0.2 (ps0.2) and 2.0 mm (ps2) for the sedimentation (SPM, ISP) and laser diffraction (LDM) measurements, was used. Here we report, based on particle size fraction contents for clay (<0.002 mm), silt (0.002-0.063 mm) and sand (0.063-2.0 mm), i) apparent deviations between pre-sieving options for each method, ii) variabilities between sample replicates (three subsamples), and iii) relationships (linear regression) and iv) texture class differences between SPM, ISP and LDM analyses. Overall, SPM showed smallest deviations between pre-sieving options, LDM largest, and ISP intermediate. Higher silt content, for ISP, and higher sand content, for LDM, seemed to be critical in the choice of optimum pre-sieving. Regarding variabilities between replicates, SPM showed smallest variabilities, ISP (especially ISP-ps0.2 and ISP-ps2) and LDM-ps2 largest, and LDM-ps0.063 and LDM-ps0.2 intermediate. SPM-ps0.063, SPM-ps2, ISP-ps2 and ISP-ps0.2 showed strongest relationships (i.e. largest R2) with the reference SPM-ps0.2, LDM-ps0.063 intermediate and LDM-ps2 weakest. Regarding texture classification, compared to the reference SPM-ps0.2, SPM-ps2 and ISP-ps2 showed largest (good, i.e. 80-100% of the cases) agreement, whereas LDM pre-sievings showed smallest (LDM-ps0.063, poor agreement, i.e. <55%). Lineartransfer transformed LDMt-ps0.063 improved the texture compatibility with SPM-ps0.2 to intermediate (63%) agreement, and SPMt-ps0.063 and ISPt-ps0.2 from intermediate (75%) to good (88%) agreement. Also clay-silt cutoff modified LDMc-ps0.063 and LDMc-ps0.2 improved the texture compatibility with SPM-ps0.2, to intermediate (63%) agreement. There is a need to continue fine-tuning methodologies to align particle size distribution composition from one method to the other, especially regarding the influence of equivalent and efficient and on the results.

This report presents the protocols and methods used 2000-2020 in the Soil Physics Laboratory at the Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden. The aim is to provide a transparent description of procedures used and to provide links and references to quality assurance and standards. Brief theoretical background and concepts are included for the different methods and procedures. New analytical techniques, such as integral suspension pressure (Pario) and laser diffraction (Horiba) methods for particle size distribution and pF laboratory station (Ecotech) for water retention properties, have been tested since 2020, but are not included in this report. For these, see technical manuals and scientific reporting.

Abstract. The soil water retention curve (SWRC) is a key soil property required for predicting basic hydrological processes. The SWRC is often obtained in the laboratory with non-harmonized methods. Moreover, procedures associated with each method are not standardized. This can induce a lack of reproducibility between laboratories using different methods and procedures or using the same methods with different procedures. The goal of this study was to estimate the inter- and intralaboratory variability of the measurement of the wet part (from 10 to 300 hPa) of the SWRC. An interlaboratory comparison was carried out between 14 laboratories, using artificially constructed, porous reference samples that were transferred between laboratories according to a statistical design. The retention measurements were modelled by a series of linear mixed models using a Bayesian approach. This allowed the detection of sample-to-sample variability, interlaboratory variability, intralaboratory variability and the effects of sample changes between measurements. The greatest portion of the differences in the measurement of SWRCs was due to interlaboratory variability. The intralaboratory variability was highly variable depending on the laboratory. Some laboratories successfully reproduced the same SWRC on the same sample, while others did not. The mean intralaboratory variability over all laboratories was smaller than the mean interlaboratory variability. A possible explanation for these results is that all laboratories used slightly different methods and procedures. We believe that this result may be of great importance regarding the quality of SWRC databases built by pooling SWRCs obtained in different laboratories. The quality of pedotransfer functions or maps that might be derived is probably hampered by this inter- and intralaboratory variability. The way forward is that measurement procedures of the SWRC need to be harmonized and standardized.

Recent studies have shown that soil particle size analyses using laser diffraction method (LDM) can give compatible results compared with traditional sedimentation based methods, if the clay-silt particle size cutoff is transformed. Additionally, procedures including separation of the sand fraction by wet sieving and running a well dispersed sample of only fractions smaller than sand during laser diffraction measurement, have given promising results. The main purpose of the present study was to test a combination of these approaches for determining cutoff transformed LDM values on 44 soil samples from agricultural sites spread over Sweden, including its compatibility with the sieve and pipette method (SPM). Furthermore, these results were compared with results of transformed LDM values based on pedotransfer functions between measured LDM and SPM. Also LDM related aspects concerning scattering parameters, repeatability and organic matter calculations were studied. To find the optimum clay-silt cutoff, Lin's concordance correlation coefficient (Lin's CCC) was calculated. The highest value (0.977) was found with the 3.409-3.905 mu m bin (a refractive index of 1.52 and an absorption coefficient of 0.1 was used). The pedotransfer-transformed LDM approach showed equally high Lin acute accent s CCC as the cutoff-transformed approach for the different soil particle fraction size classes. With the cutofftransformed LDM approach, 36 out of 44 samples were assigned to the same texture class as SPM, and with the pedotransfer-transformed LDM, the corresponding number was similar (34 out of 44 samples). The results here are promising for application in routine soil analyses, but more specific transformed clay-silt cutoffs and pedotransfer functions for LDM versus SPM should ideally be established for different types of soils. For this, microscopy and image analysis methods to help understand and quantify the influence of particle shapes on obtained particle size distributions are useful.

Few studies have explored greenhouse gas (GHG) emissions from arable land in sub-Saharan Africa (SSA), and particularly from rice paddy fields, which can be a major source of methane (CH4) and nitrous oxide (N2O) emissions. This study examined the effect of drainage on CH4 and N2O emissions from rice fields in Rwanda under shallow drainage to 0.6 m, with the drain weir open four times per week, and deep drainage to 1.2 m with the weir open four times or two times per week. CH4 and N2O fluxes from the soil surface were measured on nine occasions during rice flowering and ripening, using a closed chamber method. Measured fluxes made only a minor contribution to total GHG emissions from rice fields. However, drainage depth had significant effects on CH4 emissions, with shallow drainage treatment giving significantly higher emissions (~0.8 kg ha−1 or ~26 kg CO2-equivalents ha−1) than deep drainage (0.0 kg) over the 44-day measurement period. No treatment effect was observed for N2O fluxes, which ranged from low uptake to low release, and were generally not significantly different from zero, probably due to low nitrogen (N) availability in soil resulting from low N fertilization rate (in the region). Overall, the results suggest that deep drainage can mitigate CH4 emissions compared with traditional shallow drainage, while not simultaneously increasing N2O emissions.

The sedimentation (pipette) (SP) method has been in use for a long time as a solid reference method to estimate particle size distribution (PSD) in soil. The procedure is demanding, not the least concerning the manual extraction of soil fractions at given depth and time intervals during the sedimentation process and their subsequent drying and weighing. The more recent laser diffraction (LD) and integral suspension pressure (ISP) methods are promising alternatives. They have the advantage that the extraction-drying-weighing procedure for the finer soil fractions (clay and silt) is replaced by automatic registration of particle volumes (for LD) and pressures at given depth during the sedimentation process (for ISP). Due to these differences in measurement technics, PSD:s determined with LD and ISP methods often deviate more or less from PSD:s by SP method, which have implications for the matching with historical SP soil databases. We present some draft results of studies comparing the three methods on samples from agricultural soils in Sweden. The results show that there is still a need for further fine-tuning in the methodologies to align PSD composition from one method to the other.

Changes in pollution pressure exerted on the Rocha River in Bolivia from diffuse sources were assessed using potential non-point pollution indexes (PNPI) for 1997 and 2017. PNPI is a simple, low-effort, time- and resource-saving method suitable for data-scarce regions, as it works at catchment level with commonly available geographical data. Land use type (obtained by Landsat imagery classification), runoff (determined by runoff coefficient characterisation) and distance to river network (calculated at perpendicular distance) were each transformed into corresponding indicators to determine their relative importance in generating pollution. Weighted sum, a multi-criteria analysis tool in the GIS environment, was used to combine indicators with weighting values. Different weighting values were assigned to each of the indicators resulting in a set of six equations. The results showed that higher PNPI values corresponded to human settlements with high population density, higher runoff values and shorter distance to river network, while lower PNPI values corresponded to semi-natural land use type, lower runoff coefficient and longer distances to river. PNPI values were positively correlated with measured nitrate and phosphate concentrations at six sub-catchment outlets. The correlation was statistical significant for phosphate in 2017. Maps were produced to identify priority source areas that are more likely to generate pollution, which is important information for future management.

Forest-protected areas contribute to sequestration of CO2, but its establishment in regions where human settlements already exist conflicts with food production. There is a need to develop tools for evaluating the sustainability of land use options in such areas. The objective of the present study was to work out a procedure based on land evaluation and scenario analyses. It was tested in a study area, which is a part of a terrestrial reserve in southeastern Mexico. Requirements for agriculture and forest were matched against the variability in land characteristics to outline physical suitability for current and potential use of land. The effect on C-flux of seven scenarios with different degrees of contribution from areas of agriculture and forest in relation to current land use intensity and proportions (24% agriculture) was estimated. The scenarios were: (1) conversion of forest to agriculture (+ 24%), (2) improved land conditions by application of fertilizers (± 0% agriculture), (3) conversion of agriculture to forest (+ 12%), (4) as (1) with improved land conditions, and (5), (6), (7) as (2), (3) and (4), respectively, but with silvopastoral/agroforestry system in agriculture area. After 20 years, in relation to the start (year 0), baseline (continuation of current land use) showed a sequestration of 10356.5 Gg CO2, scenario 1 an emission of 230.1 Gg and scenario 2–7 sequestrations of 2998.5–14958.0 Gg. The methodology is promising and can be used as a framework for applications at different scales.

The tropical montane cloud forest is one of the most biodiverse ecosystems on Earth and is one of the areas most threatened by anthropogenic disturbance. This study assessed the temporal impact on soil properties (organic carbon, total nitrogen, cation exchange capacity, bulk density) following establishment of native tree species in two degraded tropical montane cloud forest areas with different soil types and land-use intensities in south-east Mexico. In Pueblo Nuevo, Chiapas, Pinus chiapensis and Alnus spp. were established at two sites with humic Nitisols with low and moderate disturbance levels, respectively. In Xalapa, Veracruz, plum pine (Podocarpus matudae), American hornbeam (Carpinus caroliniana), Oaxaca walnut (Juglans pyriformis Liebm.), and sweetgum (Liquidambar styraciflua) were established on a grassland-covered humic Andosol with a high level of disturbance. After 16 years, soil properties had generally improved, although in the initial years after planting, the values declined, indicating a possible negative impact because of disturbance during tree establishment. Land-use intensity prior to tree establishment influenced the level of recovery in soil properties. The Pueblo Nuevo sites, with low to moderate disturbance levels, regained soil quality faster than the highly disturbed Xalapa site, despite better initial soil quality in the latter.

Drainage management is important in intensification of irrigated paddy rice production. This study assessed the effects of drainage intensity on water and nitrogen use efficiency and rice grain yield in a field experiment conducted during three seasons in Rwanda. The experiment comprised 12 plots with four blocks and three treatments: DS0.6(0.6 m deep drain), DD1(1.2)(1.2 m deep drain, control structure open four times per week), and DD2(1.2)(1.2 m deep drain, control structure open two times per week). Outflow was calculated from water balance. Nitrogen (N) content in drainage water was determined weekly. Crop yield and N uptake were determined in grain and straw. In all seasons, grain yield was 61-131% higher, crop N uptake was 24-90% higher, harvest index (HI) was 24-65% higher and water use efficiency (WUE) was 50-150% higher in treatments DD1(1.2)and DD2(1.2)than in DS0.6. There was a decrease in soil carbon/nitrogen ratio at the end of Seasons 2 and 3. Recirculating straw to fields is thus necessary to replenish SOC for long-term soil fertility. A practical implication of the study is that managed deep drainage systems could enhance water use efficiency and rice grain yield in poorly drained paddy fields.

Increasing pressures caused by human activities pose a major threat to water availability and quality worldwide. Water resources have been declining in many catchments during recent decades. This study investigated patterns of river water quality status in a peri-urban/rural catchment in Bolivia in relation to land use during a 26 year period. Satellite images were used to determine changes in land use. To assess water quality, data in the dry season from former studies (1991–2014), complemented with newly collected data (2017), were analysed using the National Sanitation Foundation-Water Quality Index method and the Implicit Pollution Index method. The highest rates of relative increase in land use area were observed for forest, urban, and peri-urban areas, whereas relative decreases were observed for water infiltration zones, bare soil, shrubland, and grassland areas. The water quality indices revealed clear water quality deterioration over time, and from catchment headwaters to outlet. Statistical analyses revealed a significant relationship between decreasing water quality and urban expansion. These results demonstrate the need for an effective control programme, preferably based on water quality index approaches as in the present study and including continuous monitoring of runoff water, mitigation of pollution, and water quality restoration, in order to achieve proper water management and quality.

Increased use of irrigation on semi-arid sandy soils requires optimisation of irrigation and fertilisation practices to reduce water and nitrogen (N) losses. Field experiments were conducted on a semi-arid loamy sandy soil in two consecutive cropping periods, one in a cold-dry season (CP-cd) and one in a hot-wet season (CP-hw). The effects of individual treatment factors and their interactions, including two different irrigation methods (furrow - F or drip - D), two irrigation levels (full - I-f or reduced - I-r) and two top dressing N fertiliser types (quick - N-q or slow - N-s release), on water and N distribution in the soil profile, potential water fluxes to the zone below the roots and N losses from the 0-90 cm soil profile were studied. The concentrations of NO3-N and NH4-N in soil water (from suction cups) and soil (from bulk soil samples) tended to be higher at greater depth in the treatments with lower soil water tension, resulting from the interactions between the factors F or D with I-f and N-q, most probably resulting from net downward redistribution of N. The IrNs treatments resulted in longer soil water NO3-N and NH4-N residence time at 30 and 60 cm depth, and throughout the two cropping periods NO3-N was higher in N-s than in Nq treatments. Potential faster downward water flux, and thus water losses and the N leaching risk, was concentrated to the first 50-75 days after sowing in Fl(f)N(q) and Dl(f)N(q) treatments, while it was spread throughout the cropping periods in Fl(f) and Dl(f). Hence, treatments Fl(r)N(q) and Dl(r)N(q) in both CP-cd and CP-hw resulted in the highest estimated N losses from the 0-90 cm soil profile. Based on these results, a combination of D irrigation, I-r irrigation level and N-s fertiliser type should preferably be applied, to avoid the risk of excessive water losses, downward N redistribution and subsequent leaching. (C) 2017 Elsevier B.V. All rights reserved.

Quantification of the interactive effects of irrigation water and nitrogen (N) fertiliser on nitrogen use efficiency (NUE) provides an important insight for more effective water and N management. This study evaluated the effects of different irrigation and N fertiliser management options on water flux, N uptake, NUE and maize grain yield in a semi-arid loamy sand, in Mozambique. The experiments were carried out in field plots in two consecutive cropping periods (CP's) representing contrasting growing seasons: a hot-wet season (CP-1) and a cold-dry season (CP-2). The treatments included two irrigation methods (furrow and drip), two irrigation levels (75 and 100% of the crop water requirement), and two distinct N fertiliser types (a quick-release and slow-release urea) arranged in a randomised complete block design. In both CP-1 and CP-2, NUE tended to be higher for the 75% irrigation level, regardless of irrigation method and N fertiliser type. Higher NUE was generally observed in CP-2 than in CP-1. The highest grain NUE (41.6 kg kg(-1) N) was observed in CP-2 under furrow irrigation combined with 75% irrigation level and quick-release N fertiliser. Slow-release N fertiliser did not improve N uptake, NUE or maize yield. Potential N losses were assumed to be higher in CP-1 than in CP-2, associated with higher estimated deep percolation volumes in CP-1 (mean 127 mm) than in CP-2 (mean 12 mm). In CP-1, deep percolation events mainly coincided with high rainfall events. Furrow irrigation tended to give higher NUE than drip irrigation, especially in CP-2. Reducing of irrigation level by 25% tended to increase N uptake, NUE and maize yield for both CP-1 and CP-2. The effects of slow-release N fertiliser and drip irrigation were inconclusive. (C) 2016 Elsevier B.V. All rights reserved.

Strategies to promote dense, deep root systems are important for the efficient use of water and nitrogen fertilisers in subtropical loamy sandy soil. This study assessed the effect of interactions between irrigation method (drip and furrow), irrigation level (full and reduced), and nitrogen fertiliser type (quick release and slow-release) on root growth of maize (Zea mays L.) and the associated effect on grain yield, aboveground biomass and leaf area index. Factorial field experiments on semi-arid loamy sandy soil in Mozambique was carried out in four cropping periods (two in the hot-wet season, two in the cold-dry season). The response to the management factors at three growing stages of coarse (>= 0.7 mm diameter) and fine (<0.7 mm diameter) root density (RD) (two cropping periods) and maximum rooting depth (four cropping periods) were measured in situ by modified profile wall method. The interactions between management factors did not explain the variation in maize RD or maximum rooting depth. However, seasonal variation between the cropping periods affected the distribution of coarse RD. Drip irrigation gave 33-153% higher coarse RD and 26-55% higher fine RD than furrow irrigation in deeper layers (16-64 cm), whereas furrow irrigation gave 21-40% higher coarse RD than drip at a shallow depth (0-16 cm). Irrigation level had little effect on RD, whereas slow-release fertilisation resulted in overall higher RD, aboveground biomass and grain yield than quick-release fertilisation in the cold-dry season. RD or maximum rooting depth showed few significant correlations with grain yield, biomass and leaf area index, respectively, but higher RD generally tended to result in higher yield. Overall, drip irrigation combined with reduced irrigation and slow-release N fertiliser appeared to be the most promising strategy to promote maize rooting and increase yield, especially in the cold-dry season. (C) 2016 Elsevier B.V. All rights reserved.

In climate change scenarios, the frequency of high-intensity rain events in Sweden is assumed to increase. In a plot experiment at Ultuna, Uppsala, the influence of rain intensities on phosphorus (P) transport in the uppermost 0.5 m of a clay soil was studied at 16 locations. A rain simulator, 0.5 x 0.5 m and mounted 1 m above the soil surface, was used to simulate 85-500 min rain sequences causing small (4-9 mm h(-1)) and large (22-28 mm h(-1) and one extreme at 37 mm h(-1)) steady water fluxes (intensity) in the underlying soil profile. Water percolated to a zero-tension collector tray at 0.5 m depth where drain water and its sediment load was sampled at discrete time intervals. The total P (TP) mass flux ranged, at low intensity, between 12-92 mu g m(-2) min(-1) (average 28.1 mu g m(-2) min(-1)) and, at high intensity, between 83-375 mu g m(-2) min(-1) (average 168.5 mu g m(-2) min(-1)) and 648 mu g m(-2) min(-1) at the extreme intensity. The soluble reactive (inorganic) P (SRP) mass flux ranged, at low intensity, between 1-65 mu g m(-2) min(-1) (average 10.0 mu g m(-2) min(-1)) and, at high intensity, between 6-205 mu g m(-2) min(-1) (average 47.9 mu g m(-2) min(-1)) and 495 mu g m(-2) min(-1) at the extreme intensity. Thus, in the intensity range 4-28 mm h(-1), TP and SRP increased, on average, by approximately 12% (mu g m(-2) min(-1)) per unit increase in intensity (mm h(-1)). The results of this study demonstrate increased sediment and P loss/mobility for clay soil under increased precipitation intensity predicted under climate change.

The first step in evaluating phosphorus (P) loss risks should be to investigate the topsoil, which is generally considered a source of P transport via macropore flow. A procedure is presented for in situ measurement of hydraulic response times, critical water outflow rates, as well as turbidity (T), sediment (SC), and total phosphorus (Ptot) concentrations in outflowing soil water solution from the upper half meter of a clay soil. The method applies to a range of controlled experimental rainfall intensities from a drip infiltrometer, and a zero-tension collection tray located at 0.5m depth through which percolating water/sediment solution is sampled. Reasonable positive relationships were observed between T, SC, and Ptot versus steady output flow rates (qs). Dependencies were strong between Ptot and each of qs and T, and weaker between Ptot and SC. The methods require further validation and will be further developed in upcoming studies.

Losses of nutrients from arable land significantly contribute to the eutrophication of lakes and coastal waters. Consequently agricultural nutrient and water management strategies have been emphasized during the last decades. The problem of excessive drainage at certain times of the year in conventional drainage systems (CD) can in many cases be overcome by implementing controlled drainage strategies (CWT). The data for this paper is based on water management projects, at both plot and field scales, which have been carried out in Southern Sweden during the period 2002 to 2005. The studies included water table strategies in which the subsoil was subjected to various degrees of water status at different times of the year by means of controlled drainage system. They were run on one site with small plots and two sites with field scale plots, and each site consisted of one CD plot and three CWT plots.Compared to CD, CWT had lower subsurface runoff all years of measurement. Nitrogen (N) and phosphorus (P) concentrations in subsurface drainage water revealed no significant differences between CWT and CD. N and P losses, in contrast, tended to be lower in CWT than in CD, possibly due to lower runoff volumes in CWT. The yearly losses of NO3-N, Total-N, PO4-P and Total-P through the drainage system were on average 40% lower in CWT than in CD. The yield and N uptake by crops, in most measurements, were higher in CWT due to more water available during the cropping season and thereby improved N efficiency of the applied fertiliser. The results from the experiments revealed that controlled drainage has a potential to lower non-point source leaching of nutrients from agricultural land, improve N and P use efficiency and increase yields. (C) 2014 Elsevier B.V. All rights reserved.

Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity, K, in (eco)hydrological models ignore the effects of key site factors such as land use and climate and underplay the significant effects of soil structure on water flow at and near saturation. These limitations may introduce serious bias and error into predictions of terrestrial water balances and soil moisture status, and thus plant growth and rates of biogeochemical processes. To resolve these issues, we collated a new global database of hydraulic conductivity measured by tension infiltrometer under field conditions. The results of our analyses on this data set contrast markedly with those of existing algorithms used to estimate K. For example, saturated hydraulic conductivity, Ks, in the topsoil (< 0.3 m depth) was found to be only weakly related to texture. Instead, the data suggests that Ks depends more strongly on bulk density, organic carbon content and land use. In this respect, organic carbon was negatively correlated with Ks, presumably due to water repellency, while Ks at arable sites was, on average, ca. 2–3 times smaller than under natural vegetation, forests and perennial agriculture. The data also clearly demonstrates that clay soils have smaller K in the soil matrix and thus a larger contribution of soil macropores to K at and near saturation.