Pasture Soils Research Articles

The persistence and efficacy of nitrification inhibitors to mitigate nitrous oxide emissions from New Zealand pasture soils amended with urine

Information on the comparative effectiveness of the nitrification inhibitors (NIs), 3,4-dimethylpyrazole phosphate (DMPP) and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) on New Zealand (NZ) urine-amended pasture soils is lacking. Therefore, laboratory incubation experiments were conducted to test the half-life and efficacy of these NIs to reduce nitrous oxide (N2O) emissions from two urine-amended pasture soils varying in clay and organic matter content. Two application rates of each NI were tested as follows: 2.5 and 5 mg DMPP kg−1 soil, and 3 and 6 mg nitrapyrin kg−1 soil. Dicyandiamide (DCD) was used as a reference NI, at the recommended application rate (10 mg DCD kg−1 soil). The half-life values (at 15°C) of the NIs varied with clay and organic matter. These were 12–17 days for DMPP and 18–29 days for nitrapyrin compared with 20–33 days for DCD. All the NIs reduced N2O emissions, but their efficacy differed with the amount of NI and soil type. The reductions in N2O emissions were 19–46% with DMPP and 45–59% with nitrapyrin relative to 43–47% with DCD. The higher rate of nitrapyrin achieved significantly (p < 0.05) greater reductions under lower clay and organic matter content. The NIs did not affect the levels of soil microbial biomass carbon and nitrogen (MBC and MBN) during the study period.

In situ nitrous oxide and dinitrogen fluxes from a grazed pasture soil following cow urine application at two nitrogen rates

Cattle grazing of pastures deposits urine onto the pasture soil at high nitrogen (N) rates that exceed the pasture's immediate N demands, increasing the risk of N loss. Nitrous oxide (N2O), a greenhouse gas, and dinitrogen (N2) are lost from the cattle urine patches. There is limited information on the in situ loss of N2 from grazed-pasture systems which is needed for understanding pasture soil N dynamics and balances. The 15N flux method was used to determine N2 and N2O fluxes over time following synthetic urine-15N application at either 400 or 800 kg N ha−1 to a grazed perennial pasture soil. Results showed that daily N2O fluxes were higher under 800 kg N ha−1 than under 400 kg N ha−1, but there was no significant difference in N2 fluxes. Cumulative N2O emissions from soil with 400 kg N ha−1 and 800 kg N ha−1 applied represented 0.16 ± 0.08% and 0.43 ± 0.08% of deposited N, respectively, while emitted N2 accounted for 32.1 ± 4.1% and 14.4 ± 1.7%, respectively, over 95 days after urine application. Codenitrification and denitrification co-occurred, with denitrification accounting for 97.9 to 98.5% of total N2 production. Recovery of urine-15N in pasture decreased with increasing N rate with 14.7 ± 0.5% and 9.9 ± 0.8% recovered at 400 and 800 kg N ha−1, respectively after 95 days. The N2O/(N2 + N2O) product ratio was generally higher during periods of nitrification of urine-N (the first month after urine application) but with no clear relationship to other measured variables. Contrary to our hypothesis, an elevated urine-N rate did not enhance N2 loss. This is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers. Soil relative gas diffusivity indicated that high N2 fluxes resulted from entrapped N2 diffusing from the draining soil.

Maintaining grass coverage increases methane uptake in Amazonian pastures, with a reduction of methanogenic archaea in the rhizosphere

Cattle ranching is the largest driver of deforestation in the Brazilian Amazon. The rainforest-to-pasture conversion affects the methane cycle in upland soils, changing it from sink to source of atmospheric methane. However, it remains unknown if management practices could reduce the impact of land-use on methane cycling. In this work, we evaluated how pasture management can regulate the soil methane cycle either by maintaining continuous grass coverage on pasture soils, or by liming the soil to amend acidity. Methane fluxes from forest and pasture soils were evaluated in moisture-controlled greenhouse experiments with and without grass cover (Urochloa brizantha cv. Marandu) or liming. We also assessed changes in the soil microbial community structure of both bare (bulk) and rhizospheric pasture soils through high throughput sequencing of the 16S rRNA gene, and quantified the methane cycling microbiota by their respective marker genes related to methane generation (mcrA) or oxidation (pmoA). The experiments used soils from eastern and western Amazonia, and concurrent field studies allowed us to confirm greenhouse data. The presence of a grass cover not only increased methane uptake by up to 35% in pasture soils, but also reduced the abundance of the methane-producing community. In the grass rhizosphere this reduction was up to 10-fold. Methane-producing archaea belonged to the genera Methanosarcina sp., Methanocella sp., Methanobacterium sp., and Rice Cluster I. Further, we showed that soil liming to increasing pH compromised the capacity of forest and pasture soils to be a sink for methane, and instead converted formerly methane-consuming forest soils to become methane sources in only 40–80 days. Liming reduced the relative abundance of Beijerinckiacea family in forest soils, which account for many known methanotrophs. Our results demonstrate that pasture management that maintains grass coverage can mitigate soil methane emissions, compared to bare (bulk) pasture soil.

Treating farm dairy effluent with poly‐ferric sulphate dramatically reduces phosphorus and E. coli leaching through subsurface drains—A physical drainage model study

AbstractLand application of farm dairy effluent (FDE) may lead to water contamination, by contaminants such as phosphorus (P) and E. coli. A new FDE treatment technology using poly‐ferric sulphate (PFS) has been developed to recycle wastewater in FDE for washing the farmyard. A physical drainage model study was conducted to investigate the effect of treating FDE with PFS on phosphorus and E. coli leaching through model subsurface drains. Dissolved reactive phosphorus (DRP) and total phosphorus (TP) leaching losses from untreated effluent (FDE) averaged 3.48 kg P ha−1 and 11.44 kg P ha−1, respectively. The application of PFS‐treated effluent (TE) resulted in significantly lower DRP and TP leaching losses at 0.24 kg P ha−1 and 4.52 kg P ha−1 for fresh TE and 0.27 kg P ha−1 and 6.31 kg P ha−1 for TE stored for 3 weeks before application (TE‐S). Cumulative DRP lost to drainage water from the TE and TE‐S treatments was 93.1% and 92.2% lower than that from the FDE treatments. Compared with the FDE treatment, there was a 98.27% and 99.99% reduction in E. coli in the drainage water from the TE and TE‐S treatments. Plant biomass and P uptake were not affected by the effluent treatments. These results indicate that land application of PFS‐treated effluent, fresh or stored, on drained pasture soils can produce significant environmental benefits by reducing the concentration and amount of P and E. coli in the drainage water, without adversely impacting plant growth.

Agroecology niche for New Zealand's native earthworms

Exotic lumbricid earthworms have had some limited success colonising productive agricultural pastures in New Zealand, in place of native megascolecid species that did not adapt to the conversion from native vegetation cover. Native earthworms in lowland intensively-farmed landscapes are now almost entirely restricted to small fragments of native vegetation on marginal land where they coexist with adventive lumbricids. In recent years, regular pasture replacement using cultivation has been largely replaced by herbicide spray-out followed by direct drilling; much less soil disturbance potentially creates a new opportunity for native earthworms to colonise pastures. Reclaiming native earthworm habitat is critical not only to protecting diversity, but also to sustaining New Zealand's unique soil ecosystem services strongly associated to role of native species; however, there have been no studies related to this. Using a mesocosm experiment, we investigated how native and exotic earthworms modify physicochemical properties of a sheep-grazed pasture soil. The pasture soil was found to be equally suitable for the growth and survival of native and exotic species. Most burrowing earthworms increased the more soluble forms of macronutrients (N, P, S, K and Mg), but differences between native and exotic species were found to be larger than between functional groups. Two species of native earthworms, Octochaetus multiporus and Maoridrilus transalpinus, modified some soil properties in similar way to exotic species, but had significantly different impacts on pH, mineralisation of nutrients, and plant availability of trace elements. Compared to control, plant available N (PAN) and S concentrations were higher by more than 100% and 40%, respectively, in soils with presence of burrowing activity of the two native earthworms. Future co-existence of communities of native and exotic earthworms in agricultural pastures appears realistic, and this would benefit conservation of native species as well as dairy production. Further research may also reveal additional and unique benefits to soil quality that could be attributable to this formerly unavailable niche for native earthworms.

Effect of phosphogypsum application on aluminum speciation in acid pasture soils

Effect of phosphogypsum application on aluminum speciation in acid pasture soils

Soil alterations by chronosequence of pastures in crop-livestock-forestry systems

The intensive use of land has accelerated the loss of soil quality, a process that can be avoided by adopting conservationist production systems, such as the Integrated Crop-Livestock-Forest (CLFI system). It is noteworthy that in the Southwest of the State of Maranhão a substantial portion of soils in rural properties are degraded and in distinct stages of erosion, since they have been exploited for decades with non-properly managed pastures. Therefore, the objective of this work was to emphasize the importance of physical and chemical changes in the soil of pastures under crop-livestock-forest integration in general and in the Amazon region of state of Maranhão, Brazil. Therefore, a literature review was conducted through a search for studies in the Google Scholar database, which encompasses multiple other databases, such as Scielo, Elsevier, Scopus, Capes, and others. In face of the conditions of degradation in pastures throughout the state of Maranhão and the broad distribution of native forests such as Babassu forests, the use of technology from CLFI systems could allow for their recovery and sustainable status by means of economically and ecologically feasible productivity. Research on this field is therefore necessary to highlight short- and long-term efficiencies regarding carbon sequestration and quality of organic matter on the soil.

Cattle manure application triggers short-term dominance of Acinetobacter in soil microbial communities

Manure application improves soil productivity but also spreads microorganisms, some of which can be of clinical relevance. The ability of manure to spread common human pathogens has been widely studied but we lack understanding on whether it also disseminates opportunistic pathogens like Acinetobacter and other non-fermenting Gram-negative bacteria (NFGNB). We designed a microcosm experiment simulating the application of fresh manure to soil to analyse the effects on soil microbial communities (and vice versa), focusing on Acinetobacter and other NFGNB. We conducted two independent experiments with fresh cattle manure from a dairy farm and two pasture soils from different organic farms. We sampled the microcosms on days 2, 7, 14, 28 and 84, and characterized the microbial communities through sequencing of 16S rRNA amplicons from i) total communities and ii) those cultured on CHROMagar Acinetobacter (i.e., selective for NFGNB) after 24-h growth. Manure altered the community composition of soil microorganisms whereas the reverse effects were weaker, showing a transition to an environmentally structured community. Acinetobacter species increased their relative abundance in manure and soil under manure on day 2, especially in soils previously exposed to γ-irradiation to reduce the load of native microorganisms. Although manure spread most Acinetobacter phylotypes in the soil, it also stimulated a few from the soil that became occasionally abundant in manure. This study demonstrates that Acinetobacter species may dominate in soil and manure for a short time after deposition, and highlights their high responsiveness and competitiveness to changes likely associated with an increase in labile resources.

Increased soil moisture intensifies the impacts of forest-to-pasture conversion on methane emissions and methane-cycling communities in the Eastern Amazon

Climatic changes are altering precipitation patterns in the Amazon and may influence soil methane (CH4) fluxes due to the differential responses of methanogenic and methanotrophic microorganisms. However, it remains unclear if these climate feedbacks can amplify land-use-related impacts on the CH4 cycle. To better predict the responses of soil CH4-cycling microorganisms and emissions under altered moisture levels in the Eastern Brazilian Amazon, we performed a 30-day microcosm experiment manipulating the moisture content (original moisture; 60%, 80%, and 100% of field capacity - FC) of forest and pasture soils. Gas samples were collected periodically for gas chromatography analysis, and methanogenic archaeal and methanotrophic bacterial communities were assessed using quantitative PCR and metagenomics. Positive and negative daily CH4 fluxes were observed for forest and pasture, indicating that these soils can act as both CH4 sources and sinks. Cumulative emissions and the abundance of methanogenesis-related genes and taxonomic groups were affected by land use, moisture, and their interaction. Pasture soils at 100% FC had the highest abundance of methanogens and CH4 emissions, 22 times higher than forest soils under the same treatment. Higher ratios of methanogens to methanotrophs were found in pasture than in forest soils, even at field capacity conditions. Land use and moisture were significant factors influencing the composition of methanogenic and methanotrophic communities. The diversity and evenness of methanogens did not change throughout the experiment. In contrast, methanotrophs exhibited the highest diversity and evenness in pasture soils at 100% FC. Taken together, our results suggest that increased moisture exacerbates soil CH4 emissions and microbial responses driven by land-use change in the Amazon. This is the first report on the microbial CH4 cycle in Amazonian upland soils that combined one-month gas measurements with advanced molecular methods.

Management Zones in Pastures Based on Soil Apparent Electrical Conductivity and Altitude: NDVI, Soil and Biomass Sampling Validation

The intensification of the Montado mixed ecosystem (agro–silvo–pastoral) is a current endeavor in the context of promoting the sustainability of extensive livestock production in the Mediterranean region. Increased pasture productivity and extensive animal production involves the use of technologies to monitor spatial variability and to implement differentiated management of pasture grazing, fertilization or soil amendment. An intermediate step should lead to the identification and demarcation of areas with similar characteristics (soil and/or crop development), known as homogeneous management zones (HMZ) to implement site-specific management strategies. In this study, soil apparent electrical conductivity (ECa) and altimetry surveys were carried out in six experimental pasture fields with a non-contact electromagnetic induction sensor (EM38) associated with a Global Navigation Satellite System (GNSS) receiver. These ECa and topographic maps were used in geostatistical analyses for designing and establishing final classification maps with three HMZ (less, intermediate and more potential). The normalized difference vegetation index (NDVI), obtained from a proximal optical sensor, and soil and biomass sampling were used to validate these HMZ. From a practical perspective, these HMZ are the basis for preparation of fertilizer prescription maps and use of variable rate technology (VRT) in a Precision Agriculture project.

Draft Genome Sequence of Thermoactinomyces vulgaris Strain AGRTWHS02, Isolated from Pasture Soil of a Sheep Dairy Farm in New Zealand.

ABSTRACTThermoactinomyces species are heat-resistant spore-forming bacteria that are capable of producing proteases. Here, we report the draft genome sequence of a new Thermoactinomyces vulgaris strain, AGRTWHS02, with a strong proteolytic activity, which was isolated from a sheep dairy farm environment in New Zealand. The genome is 2.56 Mbp, with a GC content of 47.9%.

Forage crops and cadmium: How changing farming systems might impact cadmium accumulation in animals

Production advantages, environmental benefits and increasing parasite resistance are changing the composition of New Zealand pastures. Traditional ryegrass/clover pasture mixes are being replaced by forage herb crops such as lucerne, chicory and plantain that accumulate a higher concentration of contaminants such as cadmium (Cd). To explore the relationship between Cd in forage crops and the Cd concentration accumulated by animals, four-month-old lambs at four farms across the central North Island of New Zealand were grazed on different forage crops (ryegrass, chicory, lucerne and plantain) between weaning and slaughter. Soil and pasture samples, and sequential liver biopsies, were collected and analysed for total Cd. There were significant differences in Cd concentration between the forage crops (chicory > plantain > lucerne > ryegrass) and this ordering was repeated for Cd in liver. There was no exceedance of maximum limits (ML) for Cd in offal set by the EU and NZ/Australia food safety standards authorities for animals of this study, although the highest concentration of Cd in chicory (0.85 mg/kg DW) was considerably lower than has been recorded elsewhere in New Zealand (4.5 mg/kg DW). Provisional Soil Management Values (SMVs) were developed to explore compliance of liver with EU food standards as a function of grazing chicory. For a soil pH of 5, exceedance might occur at a soil cadmium concentration of 0.34 mg/kg. This concentration falls within Tier 0 of the New Zealand Tiered Fertiliser Management System which seeks to ensure soil Cd remains within acceptable limits over the next 100 years and beyond. Increased Cd uptake by fodder crops and its management in these Tier 0 pastoral soils is therefore an emerging issue for pastoral agriculture. The risk of ML exceedance for animals grazing forage crops such as chicory on low Cd soils should be further considered to ensure uninterrupted access to export markets.

Assessment of the Wetland Ecosystem Services Status and Their Uses in the Barotse Flood Plains of Zambezi Sub Basin, Zambia

The Zambezi River Basin system and wetlands in particular, have a high ecosystem services and economic value to large number to people the study aim was to assess the status of ecosystem services and their benefits in the wetlands of Barotse Flood plains (BFP). The study utilized both secondary and primary data sources. Primary data was collected using interview schedule, key informant’s interviews, Participatory rural appraisal and field observations. Simple random sampling was used to select proportional respondents from 9 district that are found study area. The wetland ecosystem services that were identified in BFP are: Provisioning which include water, fish, wild game, fruits, edible plants, reeds, sedge, pasture, thatching grass, sand and clay soil, and medicinal plants. Regulation; climate regulation (temperature and precipitation), ground water discharge and river flow regulation. Cultural; traditional ceremonies, sacred places and recreation. Support services; soil formation, alluvial and organic matter. The study found that the ecosystem services were affected by socio-ecological factors in the BFP that led to declining of ecosystem services in general. The Pearson coefficient correlation showed that there is a significant relationship of 0.930** at 0.01 level between socio-ecological factors and declined ecosystem services in BFP. The study recommended strategies such as the government, local leadership and other stakeholders to embark on protection and conservation of BFP since it is a recognized and designated Ramsar heritage site. Government also to embark on formulating new policies on ecosystem services management in the wetlands and to fully implement the already existing policies.

A device to simulate contaminant transfer and surface and subsurface flow through intact soil monoliths

AbstractMany contaminants of agricultural origin are released into rural environments, particularly at the soil surface. Their fate has been extensively investigated in repacked soils, but only few studies have addressed their transport in structurally preserved natural soils. Much remains unknown about their fate and transfer within and between environmental compartments, while the susceptibility of these compartments to the contaminants adverse effects can vary considerably. The lack of studies regarding surface and subsurface transfer of contaminants through intact soil compared with studies on repacked soil led us to propose a device and protocol for sampling intact soil monoliths (60 × 30 × 22 cm3, length, width, depth [LWD]) without heavy machinery. This is achieved by a modular design with removable top and bottom lid and a protocol of cutting the soil and replacing the affected bottom soil with a drainage layer of glass beads. The device allows the application of artificial rainfall events with simultaneous highly resolved quantification of infiltration excess overland flow and drainage discharge. It is designed to facilitate the collection of samples for physical, biological, and chemical analyses that fulfill cleanliness standards for organic contaminant analysis at trace levels using only poorly reactive stainless steel and glass materials. Testing of the device was performed by measuring the transfer of the antiparasitic drug ivermectin (IVM) through and over a silt‐loam pasture soil. This test case illustrates how the device can be used to gain valuable information on the transfer of trace organic contaminants through topsoils.

Spring pasture renewal involving full inversion tillage and a summer crop can facilitate soil C storage, improve crop yields and lower N leaching

Soil organic carbon (SOC) sequestration in pastoral soils could offset net greenhouse gas emissions by reducing global atmospheric carbon dioxide (CO2) concentrations and, thereby, slow climate warming. Long-term pastures typically have topsoils (0–10 cm) rich in SOC, with subsoils (10–30 cm) storing less than half as much SOC. In New Zealand, lowland farmers are advised to renew (reseed) their pastures every 7–10 years to improve pasture production. Renewal typically involves desiccating the old pasture followed by shallow tillage (or direct drilling) to establish a short season forage crop as a weed break, then direct drilling new pasture species. Minimum till at renewal maintains the vertical stratification of SOC, limiting the scope to increase SOC stocks under new pasture. During the spring of 2016 and 2017, two independent trials were established, on an Alfisol (trial 1) and on an Andisol (trial 2), to assess the effects of establishing a summer Brassica crop with either full inversion tillage (FIT; 30 cm furrow depth, as a one-off or infrequent (every 25–30 years) management), shallow tillage or no-till (direct drill) on SOC stocks and crop/pasture agronomic performance. In autumn, new pasture species were direct drilled into the stubble of the summer forage crop. Changes in SOC vertical distribution, plant growth, herbage quality (at both trials) and nitrogen (N) leaching (trial 1 only) were monitored. At both trials, FIT effectively buried SOC below 0–10 cm depth and increased crop yields compared to no-till treatment. After re-grassing pasture production was similar among all treatments. In trial 1, N leaching losses were 42% lower under FIT than under no-till. These results highlight the potential agronomic and environmental benefits of pasture renewal including FIT. Economic and N cycling benefits depend on the timely inclusion of a crop phase.

Physical attributes and organic material in pastures of Brachiaria brizantha at degradation levels

Pastures cover, in Brazil, around 165 million ha, most of them are at some degradation level. Recovering these pastures is essential. The objective of this study was to evaluate the sensibility of soil organic matter (SOM) and its physical attributes in pasture soil at different degradation levels (1 to 4), Capoeiras (1 and 2) and secondary Forest (Control). Samples were collected at four depths (0.00-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.40 m). We verified higher values for SOM and hydraulic conductivity (Ko) in Forest, especially in the most superficial layer (0.00-0.05). We noted low values for macroporosity in this area. In all areas under Pastures lower values for Ko were observed in the superficial layer (0.00-0.05 m) when compared to layers 0.05-0.10 and 0.10-0.20 m, which indicates that the pasture management and cattle trampling negatively affect the physical quality of the pastures. For field capacity and wilting point the average values were observed in Pasture 4 (more degraded), which caused higher values for water availability. According to the principal components analysis, except for SOM at 0.20-0.40 m, all variables studied presented correlation above 0.6. From grouping analysis, we separated 3 groups: Forest; Capoeiras 1 and Capoeira 2 and Pastures 1 to 4.

Nitrous oxide responses to long-term phosphorus application on pasture soil

ABSTRACT Nitrous oxide (N2O) is a greenhouse gas emitted from grazed pasture systems. The influence of phosphorus (P) fertility on these emissions is not understood. This study examined if fertiliser P affected N2O emissions following nitrate application to soil from the Winchmore long-term P fertiliser trial. We hypothesised increasing P fertility would enhance soil carbon (C) supply and N2O emissions via denitrification. Using mesocosms, N2O and CO2 fluxes were measured over 29 days following KNO3-15N and glucose additions, along with soil chemical and biological variables. Microbial biomass P increased (P < 0.001; R 2 = 98.2%) with increasing Olsen-P. Fertiliser P enhanced net N mineralisation. Cumulative CO2 fluxes were unaffected by P treatment regardless of KNO3 addition. Fluxes of N2O increased one day after KNO3 addition with higher emissions at 250 kg ha−1 of superphosphate. Relatively low N2O-15N enrichment indicated minor denitrification contributions to the N2O flux. Subsequently, glucose addition enhanced N2O-15N enrichment and denitrification in the KNO3 treatment. Following glucose addition, the emission factor increased with P fertiliser. Denitrification derived N2O emissions will increase with P fertilisation but only if C limitation is overcome.

Aggregation Index and Carbon and Nitrogen Contents in Aggregates of Pasture Soils under Successive Applications of Pig Slurry in Southern Brazil

Pig slurry (PS) applications affect soil aggregation and carbon and nitrogen contents in aggregates. The objective of this study was to evaluate changes caused by successive applications of PS and mineral fertilizer on soil aggregation and carbon (C) and nitrogen (N) contents in aggregates of a clayey Typic Hapludox cultivated with Cynodon dactylon cv. Tifton-85 in southern Brazil. The treatments consisted of six annual applications of PS (100, 200, 300, and 400 kg N ha−1) and urea (200 kg N ha−1), and a control with no fertilizer application. Soil samples were collected in March 2019 and evaluated for aggregate stability, through the geometric mean diameter of aggregates (GMD), and GMD sensitivity index (SIGMD), and mass of macro-, meso-, and microaggregates. Total organic carbon and nitrogen contents were determined in macroaggregates and microaggregates. Applications of PS to pasture soils increase dry matter production of Tifton-85 and can increase soil aggregation by increasing the mass of macroaggregates. The highest PS rates decreased aggregate stability, resulting in lower macroaggregate mass, GMD, and SIGMD, and higher microaggregate mass. PS applications to pasture soils can increase C and N contents in macro and microaggregates, and improve soil aggregation when using the rates of 100 or 200 kg N ha−1, mainly in subsurface layers.

Humus of the brown soils of the mountain pastures of Uzbekistan

The aim of the study: assessment of humus content and its distribution in the profile of brown soils of mountain pastures in Uzbekistan. Location and time of the study. Soil pits were cut in the Republic of Uzbekistan in seven agricultural regions, widely used in agriculture: Tashkent region, Bustonlik district; Jizzakh region, Zomin district; Samarkand region, Nurabad district; Navoi region, Nurata district; Kashkadarya region, Kitab district; Surkhandarya region, Sherabad district; Namangan region, Papal district. The study was carried out in 2019-2021. Methods. Field studies, sampling and sample preparation were carried out in accordance with the generally accepted methods: soil organic carbon content was measured by bichromate digestion, carbonate content was determined by acidimetric method and soil inorganic carbon content was calculated by subtracting from the total content of carbonates. Silty fractions were isolated by centrifugation. Humus differentiation into reserves and their estimation was carried out according to the method proposed by one of the authors. Main results. The studied brown soils of mountain pastures of Uzbekistan are characterized by loamy granulometric composition, with a clay fraction not exceeding 20%. The content of carbonates is low (2.5–9%), with the maximum amount in the carbonate horizon. Soils are slightly leached. The total humus content in the upper horizon varies from 1% to 6.6%. The dependence of soil humus content on the slope exposure was noted: the soils of the more humid northern and western slopes contain more humus than the southern and eastern ones. In addition, the humus content is significantly affected by erosion. To assess the nature of changes in the organic matter of the brown soils during their agricultural use, humus of the near, labile and potential reserves (as percentage of the total content) was isolated for the first time. It was revealed that humus of potential reserve prevails in soils (35.5-90%). Its vertical distribution is characterized by a sharp decrease in the sub-humus part, while the humus of the near and labile reserves is distributed evenly in the profile, without a pronounced dependence on external conditions and the degree of disturbance. The proportion of insoluble organic substances in the total humus content ranged from 0.39 to 86%, of sparingly soluble organic substances - from 3 to 100%. There is a relationship between the amount of sparingly soluble and insoluble organic matter in the upper horizon and the degree of soil erosion. Conclusion. The distribution of humus and its reserves in the brown soils of the mountain pastures of Uzbekistan is uneven and strongly affected by erosion. The loss of near and labile humus reserves leads to a decrease in the content of total humus. Further study of humus features, humus accumulation and restoration in brown soils is important for the development of recommendations for the rational use, anti-erosion protection and increasing the productivity of mountain pastures in Uzbekistan.

A comparison of the threshold concentrations of DCD, DMPP and nitrapyrin to reduce urinary nitrogen nitrification rates on pasture soils – a laboratory study

Context Using nitrification inhibitors (NIs) for the targeted management of urine patches, to reduce nitrous oxide (N2O) emissions, requires determining the threshold concentrations of the NIs in urine for effective nitrification inhibition. Aims This study comparatively assessed the threshold concentrations of three NIs: dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP) and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) to reduce urinary nitrogen (N) nitrification rates on two contrasting pasture soils. Methods Four rates of each NI (3–27 mg DCD kg−1 soil, 1–13 mg DMPP kg−1 soil and 1–14 mg nitrapyrin kg−1 soil) were added to urine-amended soils and incubated at laboratory room temperature. The amended soils were sampled periodically to monitor changes in mineral-N concentrations. Key results The threshold concentration of DCD (3 mg kg−1 soil, lowest rate tested) was lower than that of nitrapyrin (5–7 mg kg−1 soil) and DMPP (13 mg kg−1 soil, highest rate tested) on both soils. Greater NI effectiveness corresponded to greater NI persistence, with higher (P &lt; 0.05) half-life values observed for DCD (16 ± 2 days, mean ± s.e.) compared with nitrapyrin (10 ± 2 days) and DMPP (9.2 ± 0.3 days). All three NIs persisted longer (P &lt; 0.05) with higher application rates. Conclusions Compared with DCD and nitrapyrin, a higher DMPP concentration was required to effectively inhibit urinary N nitrification rates in the pasture soils. Implications Choosing the ideal application rate of NIs to inhibit nitrification under field condition, and hence mitigate N2O emissions from urine patches, requires consideration of the factors that affect NI loss.