Soil Population Density Research Articles

Development of a Damage Function Model for Pratylenchus penetrans on Corn.

The lesion nematode Pratylenchus penetrans is a common pest of corn in the north-central United States. There are relatively few studies documenting the impact of Pratylenchus spp. on grain yield even though they are recognized as pests of corn and the target of commercial seed treatments. We adapted a component error modeling approach to develop a damage function for P. penetrans that included the influence of year and site in the yield loss relationship. Field data from six site-years was used to derive panel data consisting of all pairwise comparisons of the difference in nematode population densities and the associated proportional yield difference. Fourteen regression models of the relationship between proportional yield loss and the difference in nematode density were developed from soil and root assays at different corn growth stages. Seven models were significant: four models based on nematode population densities in soil (initial and final samples) and three based on nematode densities in seminal roots (corn growth stages V1 to V2 and V6) and adventitious roots (corn growth stage R1 to R2). The model we consider to be the most important, that based on the initial soil assay, estimated the yield loss caused by each nematode to be 0.0142%. The grand mean of the 118 plots we sampled implied a yield loss of 3.79%. The random effects of year and field did not contribute significantly to any of the models but were close to significance for some, suggesting a benefit from larger data sets. Experimental error was the largest component of the variance for all of the models; therefore, the damage function is more useful for demonstrating impact of P. penetrans rather than for accurately predicting yield loss at the field level. All of the fields in our study were an irrigated loamy sand soil, with grain yields above the county average; therefore, it is possible that our damage function is conservative. The value of soil sampling has been questioned for P. penetrans and this study shows it to be equal to if not better than root assays for predicting yield.

Long-term effect of Tylenchulus semipenetrans on citrus tree quality in reclaimed land of Egypt

Citrus fruit yield is considered a short-term response to the citrus nematode,Tylenchulus semipenetrans damage and therefore this study addressed parametersmeasuring overall appearance of the sampled trees. Soil and roots from 20 trees ineach of three mature: 'banzaheer' lemon, 'Baladi' mandarin, and ‘Navel’ orange andone immature: ‘Navel’ orange orchards, all grafted on sour orange rootstock, inEgypt were sampled for the citrus nematode, T. semipenetrans, in February 2011 toinvestigate their correlations with tree parameters (tree height and vigor, canopydiameter, and trunk circumference) that reflect long-term nematode damage of thesampled trees. The correlation between pairs of these four parameters were alwayspositive and generally with high significant levels. Each of the four parameters wasnot significantly correlated with fruit yield of the mature trees but each of tree heightand vigor, and canopy diameter was correlated with fruit yield of the immature Navelorange. The relationships between pairs of these biotic parameters and T.semipenetrans population density in fibrous roots and soil were not consistent.Eleven edaphic factors in mandarin and mature orange orchards were measuredand compared. Both soils were dominated by rough grainy particles of sand. Levelsof potassium, calcium, phosphorus, ammonium and nitrate as well as soil solutionpH, organic matter content and electric conductivity in the soil samples weresignificantly (P ≤ 0.01) different between the mandarin and orange orchards. Toachieve better economic revenue of citriculture, local tackling of T. semipenetransproblem in newly reclaimed areas of Egypt was discussed.

Genetic variation and selfing rate in Lychnis flos-cuculi along an industrial pollution gradient.

We studied nine populations of a meadow mixed-mating plant Lychnis flos-cuculi growing in a gradient of copper smelter emissions. We hypothesize that metal tolerant populations in the polluted areas have experienced a loss of genetic variation and are more selfing than the populations from the unpolluted areas. One hundred and thirty-five parental plants and 1059 offspring were genotyped with six microsatellite markers. Selfing rates were assessed manually, with Rmes, Mltr and Colony2. Soil toxicity, population density and pollinators' activity were estimated in the studied areas. Populations from the heavily polluted area have experienced a strong founder effect. However, at present, they are characterized by high densities. A recent genetic explosion was registered for the population from the most polluted site, probably due to forest thinning under pollution effects. Selfing rates estimated with different approaches agreed well only for populations with high genetic variation; they comprised 0-0.23 and were similar between polluted and clean areas. Self-fertilization in L. flos-cuculi hardly represents a mechanism for the fixation of advantageous alleles and a barrier for gene flow from non-tolerant populations. The employment of different methods of selfing rate estimation in populations with low genetic variation appears to be necessary, though not a guarantee of reliable conclusions.

Rotação e sucessão de culturas para o manejo do nematoide reniforme em área de produção de soja

O nematoide reniforme (Rotylenchulus reniformis) tem se tornado crescente problema fitossanitário da cultura da soja. Considerando a limitada disponibilidade de cultivares de soja que aliem resistência ao nematoide a outras características agronômicas desejáveis, estuda-se a possibilidade de utilização de manejo cultural para seu controle. Este trabalho visou avaliar o efeito da rotação de culturas no verão com milho, Crotalaria ochroleuca ou soja; e o manejo de entressafra, com Brachiaria ruziziensis como espécie de cobertura ou pousio. O experimento foi implantado em solo naturalmente infestado pelo nematoide reniforme (1245 nematoides/200cc de solo) em delineamento experimental de blocos ao acaso, com quatro repetições, em esquema fatorial 3x2 (cultivos de verão x manejo de entressafra). Foram avaliadas a densidade populacional do nematoide no solo e sua variação durante as safras e entressafras, bem como a produtividade da soja na safra subsequente à rotação de culturas. Não houve efeito do manejo da entressafra com braquiária sobre o nematoide. A rotação de culturas com milho ou crotalária no verão propiciou redução da densidade populacional do nematoide reniforme em comparação ao monocultivo de soja, com reflexos positivos sobre a produtividade de soja na safra seguinte

Optimizing Trehalose-Based Quantification of Live Eggs in Potato Cyst Nematodes (Globodera rostochiensis and G. pallida).

Integrated management of potato cyst nematodes (PCN; Globodera rostochiensis and G. pallida) relies heavily on the determination of cyst population densities in soil as well as the viability of the eggs inside the cysts. This study aimed to optimize a quantitative method to determine the number of viable eggs of PCN based on trehalose present in live eggs. Trehalose was extracted from cysts and from a dilution series of eggs and quantified. More trehalose was detected when cysts were crushed than when left intact. Reaction volumes were adapted to the number of eggs because small reaction volumes hampered an accurate extraction of trehalose. A maximum of 10.5 eggs/μl of reaction volume should be used to obtain a significant linear relationship between detected trehalose content and egg numbers. The sensitivity of the trehalose-based method was evaluated by determining the lowest egg detection limit and was defined as five viable eggs. The reliability of this method was tested by comparing efficacy with that of two commonly used assays, visual assessment and hatching test. The trehalose-based method gave viability results similar to those of the visual assessment, which is time consuming, requires trained personnel, and can involve some subjectivity. The hatching test identified fewer viable eggs than the other two methods. In addition, the viability of dead eggs (heated and naturally dead) was tested. No false-positive results (dead eggs declared viable) were obtained with the trehalose-based method. The robustness of the test was demonstrated by measuring the viability of eggs of PCN in different experiments repeated in time. The viability assessment method based on trehalose proved to be an objective as well as sensitive, reliable, robust, fast, and cheap technique for assessing the number of viable eggs in PCN cysts.

Ecology ofMeimuna mongolica(Hemiptera: Cicadidae) Nymphs: Instars, Morphological Variation, Vertical Distribution and Population Density, Host-Plant Selection, and Emergence Phenology

The cicada Meimuna mongolica (Distant) (Hemiptera: Cicadidae) is one of the most important pests of economic forest in Guanzhong Plain of Shaanxi Province, China. Information about ecological characteristics and some sustainable control measures of this species is urgently required for its control. In this study, nymphal instars, morphological variation, vertical distribution, and population density in soil, and emergence phenology of nymphs of M. mongolica on three main host plants (Pinus tabuliformis Carr., Populus tomentosa Carr., and Pyrus xerophila Yü) were studied, based on combined morphological and molecular identification, investigation of the first-instar nymphs hatched from eggs and others excavated from soil, and investigation of exuviae in the adult emergence period. Five nymphal instars of M. mongolica were redetermined according to the distribution plots of the head capsule widths of the nymphs. Nymphs of third and fourth instars showed morphological variation, which is closely related to host-plant association. The mean densities of nymphs in soil under the three host plants were significantly different, indicating a distinct host preference. The nymphs could extend their distribution from the 0–10 cm soil layer to the 51–60 cm soil layer underground but not beyond 60 cm soil layer under all the three host plants. The 21–30 cm soil layer under all the three host plants has the highest nymphal population density. The sex ratio of the entire population was nearly 50:50, but males dominated in the early half of the duration of the emergence. These ecological characteristics of M. mongolica could provide important information for sustainable control measures.

Incidence and management of plant parasitic nematodes under continuous vegetable production in a rainforest agroecology in Nigeria

SummaryField studies were conducted in 2012 and 2013 in the tropical rainforest zone of Nigeria to investigate the effects of a composted, pelletised organo-mineral fertiliser applied as an organic amendment at 5 metric tonnes (MT) ha-1 or at 10 MT ha-1 in four replications, on soil population densities of five genera of plant-parasitic nematodes and on crop yields of Telfairia occidentalis (fluted pumpkin). The experimental field was naturally infested with Meloidogyne incognita, Tylenchus spp., Helicotylenchus spp., Hirschmaniella spp., and Longidorus spp. The compost was applied as an amendment to soil planted with T. occidentalis 3 weeks after seedling emergence. At the end of both annual experiments, the addition of compost as a soil amendment resulted in 16.25 - 65.75% reductions in the populations of all five genera of plant-parasitic nematodes compared to an increase in each nematode population in the untreated control plots. There was also a higher crop yield of T. occidentalis in all eight treated plots compared to the control plots. Compost applied at 10 MT ha-1 reduced the soil populations of all nematode species significantly, with correspondingly higher yields of the crop compared to 5 MT compost ha-1 in both years of study. Correlation analysis showed that the population density of each nematode species had a negative effect on the cumulative leaf biomass (fresh weight) of the test crop. The results of this study suggest that nematodes constrained the production of T. occidentalis under continuous cropping and that a composted, pelletised organo-mineral fertiliser, applied as a soil amendment at 10 MT ha-1, suppressed soil populations of all five nematodes significantly and increased yields of T. occidentalis by 109 - 366% compared to the untreated control plots.

Occurrence and Development of the Cereal Cyst Nematode (Heterodera avenae) in Shandong, China

The cereal cyst nematode (CCN), Heterodera aveane, has been found in 16 provinces of China, including the Shandong winter-wheat-growing region. This study investigated the population dynamics of H. avenae in the winter wheat 'Jimai 22' and 'Tainong 18' for two consecutive years in the field. Soil and root samples were collected during the winter-wheat-growing season and H. avenae population densities and life-stages determined. H. avenae population dynamics in roots and soil of the two winter wheat cultivars were similar over the 2-year period. Second-stage juvenile (J2) population densities in wheat roots were greatest during booting stage (April), when mean soil temperature was between 11.8 and 14.4°C. Cysts in rhizosphere soil increased significantly when new cysts were formed after Zadoks (Z) 47 (booting stage). There was a peak in J2 population densities in soil during Z23 and Z30 (tillering and stem elongation, respectively) whereas J2 population densities were the lowest at Z13 (seedling stage). This research provides important information indicating that J2 populations in roots and soil increased after the wheat winter dormancy period. Knowledge of when different life stages of H. avenae occur in winter wheat in Shandong will provide valuable insights to enable the development of an integrated approach to manage this plant-parasitic nematode.

Impact of Pratylenchus penetrans on Established Red Raspberry Productivity.

The plant-parasitic nematode Pratylenchus penetrans is a major constraint to the production of red raspberry. To determine whether several popular raspberry cultivars in Washington State differ in susceptibility to P. penetrans and whether post-plant nematicides treatments are warranted, five independent, multiyear trials were conducted. Trials in existing plantings of 'Cascade Bounty', 'Chemainus', 'Meeker' (two trials), and 'Saanich' raspberry were established in northwest Washington. Treated plots were protected from P. penetrans by applying nematicides over a 3-year period, while nontreated plots received no nematicides. P. penetrans population densities in soil and root samples were assessed spring and fall of each year. In addition, impact of P. penetrans on raspberry yield, fruit composition, cane production, and root biomass was measured several times in each cultivar during the 3-year study. P. penetrans root population densities in nematicide-treated plots were consistently lower than those in nontreated plots at all the samplings. There were few consistent treatment differences in fine root biomass, the preferred feeding sites for P. penetrans. However, a complete root system sampling of one of the cultivars did show greater fine root biomass in treated plants compared with nontreated plants. When differences were observed aboveground, treated plants yielded less than corresponding nontreated plants, indicating that the nematicides may have been phytotoxic to some of the cultivars. This study suggests that post-plant nematicide applications are of limited benefit because, at least during the 3-year time period of this study, there were few observable benefits of protecting these raspberry cultivars from P. penetrans.

Causal relationships versus emergent patterns in the global controls of fire frequency

Abstract. Global controls on month-by-month fractional burnt area (2000–2005) were investigated by fitting a generalised linear model (GLM) to Global Fire Emissions Database (GFED) data, with 11 predictor variables representing vegetation, climate, land use and potential ignition sources. Burnt area is shown to increase with annual net primary production (NPP), number of dry days, maximum temperature, grazing-land area, grass/shrub cover and diurnal temperature range, and to decrease with soil moisture, cropland area and population density. Lightning showed an apparent (weak) negative influence, but this disappeared when pure seasonal-cycle effects were taken into account. The model predicts observed geographic and seasonal patterns, as well as the emergent relationships seen when burnt area is plotted against each variable separately. Unimodal relationships with mean annual temperature and precipitation, population density and gross domestic product (GDP) are reproduced too, and are thus shown to be secondary consequences of correlations between different controls (e.g. high NPP with high precipitation; low NPP with low population density and GDP). These findings have major implications for the design of global fire models, as several assumptions in current models – most notably, the widely assumed dependence of fire frequency on ignition rates – are evidently incorrect.

Nemato-toxic potential of Betel (Piper betle L.) (Piperaceae) leaf

In vitro and in-planta trials were conducted to determine the nemato-toxic potential of aqueous leaf extracts of Betel (Piper betle L.) against the root-knot nematode species, Meloidogyne incognita, at five concentrations, standard extract (S) [1:2 (w/v] and its four dilutions, 20%, 40%, 60%. 80% of S. In the in vitro trials, second-stage juveniles (J2s) and eggs of M. incognita were directly exposed to the extract while in the in-planta trials, the effect of the extract was evaluated as a root dip treatment using tomato plants. The findings indicated that the extract was lethal to J2s but also inhibited egg hatch. The seedling dip treatments reduced root infestations in terms of gall formation, egg production and J2 population densities in soil while simultaneously enhancing the growth of tomato plants. All these effects varied in a dose-dependent manner. Based on the LC50 value, the eggs were found to be less sensitive to the extract than J2s. One hundred percent of mortality of J2s was recorded at four concentration levels, 40%, 60% and 80% of S and S, while 100% egg inhibition was only recorded at S. The highest reductions in gall formation (i.e., number of galls/root system), egg production and J2 population were all recorded at S as 83%, 87% and 84% compared to the untreated water control. The maximum growth enhancement, which was 235% of the control, was detected in the root length of treated tomato plants. It appears the aqueous leaf extract of P. betle shows promise as a sustainable eco-friendly nematicide for the management of M. incognita.

Thermal time requirements of root-knot nematodes on zucchini-squash and population dynamics with associated yield losses on spring and autumn cropping cycles

The present research was undertaken to evaluate the effects of soil temperature on the life cycle of root-knot nematodes (RKN) on zucchini-squash in growth chambers and to assess the relationship between Meloidogyne incognita soil population densities at planting (Pi), its multiplication rate, and crop losses of zucchini in field conditions. Thermal requirements for M. incognita and M. javanica were determined by cultivating zucchini plants in pots inoculated with 200 second stage juveniles (J2) of each Meloidogyne species at constant temperatures of 17, 21, 25, and 28 °C. Number of days from nematode inoculation until appearance of egg laying females and until egg hatching were separately recorded. For life cycle completion, base temperatures (Tb) of 12 oC and 10.8 oC and accumulated degree-days above Tb (S) of 456 and 526, were estimated for M. incognita and M. javanica, respectively. The relationship between fruit weight and M. incognita Pi fits the Seinhorst damage function, but differed accordingly to the cropping season, spring or autumn. Tolerance limits for M. incognita on zucchini were 8.1 J2 per 250 cm3 of soil in spring and 1.5 in autumn cropping cycles, and the minimum relative yields were 0.61 in spring and 0.69 in autumn. Zucchini-squash was a poorer host for M. incognita in spring than in autumn, since maximum multiplication rates (a) and equilibrium densities (E) were lower in spring (a = 16–96; E = 274–484) than in autumn (a = 270–2307; E = 787–1227).

EFFICACY OF DIMETHYL DISULFIDE (DMDS) IN THE CONTROL OF THE ROOT-KNOT NEMATODE MELOIDOGYNE INCOGNITA AND THE CYST NEMATODE HETERODERA CAROTAE ON CARROT IN FIELD CONDITION IN ITALY

ISHS VIII International Symposium on Chemical and Non-Chemical Soil and Substrate Disinfestation EFFICACY OF DIMETHYL DISULFIDE (DMDS) IN THE CONTROL OF THE ROOT-KNOT NEMATODE MELOIDOGYNE INCOGNITA AND THE CYST NEMATODE HETERODERA CAROTAE ON CARROT IN FIELD CONDITION IN ITALY

Soil allelochemical residue effects of nemafric-BL and nemarioc-AL phytonematicides on soil health, growth of sweet sorghum and Meloidogyne species

A field trial was initiated to investigate the post-treatment effects of soil allelochemical residue (SAR) of nemafric-BL and nemarioc-AL phytonematicides on soil health, growth of sweet sorghum (Sorghum bicolor) and population densities of Meloidogyne species. SAR conditions were created in tomato (Solanum lycopersicum) trials, with treatments comprising untreated control, nemafric-BL 3%, nemafric-BL 6%, nemarioc-AL 3% and nemarioc-AL 6%, which were applied at empirically established intervals for a 56-day crop cycle. Soil preparation was followed by a 30-day fallow to allow for microbial decomposition of root remnants. Sweet sorghum seeds were sown on spots where tomato plants grew and soil samples were collected for determining the soil health status at two-leaf stage. At 80 days after sowing, SAR effects improved soil health and contributed 8% in total treatment variation (TTV) of chlorophyll and sugar contents each in sweet sorghum, with nemarioc-AL 3 and 6% phytonematicides stimulating improvement of the two variables. Nemafric-BL SAR effects had no effect on growth of sweet sorghum. In contrast, SAR effects contributed 76 and 39% in TTV of nematode population densities in root and soil, respectively. SAR effects of nemafric-BL and nemarioc-AL inhibited nematode numbers by 67–97% and 64–80%, respectively. In conclusion, SAR effects on soil health, plant growth and nematode population densities were desirable, suggesting that the two products were each still active in the soil.

Survey of Plant-Parasitic Nematodes in Kansas and Eastern Colorado Wheat Fields

Observations on the prevalence and abundance of plant-parasitic nematodes were made from soil and root samples collected from 2,640 wheat fields in Kansas and Colorado during 2007-2010. Stunt nematodes (predominately Merlinius brevidens and Quinisulcius acutus), root-lesion nematodes (predominately Pratylenchus neglectus), and pin nematodes (Paratylenchus projectus) were the most commonly encountered taxa. Maximum soil population densities of 6,520 and 1,880 nematodes/100 cm3 soil were observed for pin and stunt nematodes, respectively, while a maximum root population density of 90,309 nematodes/g dry root was observed for root-lesion nematodes. Lower nematode densities were associated with wheat following corn, grain sorghum, or soybean for pin and stunt nematodes, and with wheat following fallow for root-lesion nematodes. Based on the results of this survey, 6% and 8% of wheat acreage in the central Great Plains are estimated to be at risk for significant (>5%) yield loss due to stunt nematodes and root-lesion nematodes, respectively. The number of fields with high population densities of both stunt and root-lesion nematodes was negligible (1%); therefore, the total wheat acreage with nematode populations above provisional economic thresholds is estimated to be ∼13%. Damage relationships with greater accuracy, precision, and relevance are necessary to establish reliable yield loss estimates for this region. 3 June 2014. 11 August 2014.

N2O emission from cropland field soil through fungal denitrification after surface applications of organic fertilizer

Agricultural fields are one of the largest anthropogenic sources of atmospheric nitrous oxide (N2O). Fungi have been suggested to contribute substantially to N2O emission in terrestrial environments; however, the extent of the fungal contribution and the phylogenetic and physiologic nature of related fungal communities in agricultural fields are largely unknown. This study focused on the large N2O emission from cropland soil that occurs after granular organic fertilizers were applied to the surface. The granular organic fertilizers applied were evidently covered by fungal mycelia. An experiment using a soil microcosm was established to imitate the field observations. N2O emissions following surface organic fertilization were suppressed by 84 and 20% after the addition of cycloheximide (a fungal inhibitor) and streptomycin (a bacterial inhibitor), respectively, suggesting that fungi provide the main contribution to the observed N2O emission. The population density and community composition of fungi in the surface-fertilized and non-fertilized soils in the field were determined using colony counting, denaturing gradient gel electrophoresis and subsequent phylogenetic analyses. Thirty-four fungal strains were isolated from the soils, and their N2O producing activities were analyzed. Fungal population density in the surface-fertilized soil (2.6 × 106 CFU/g) was much higher than that in the non-fertilized soil (1.0 × 105 CFU/g). In addition, the fungal community compositions of the soils differed. Actinomucor elegans, Bionectria ochroleuca, Fusarium avenaceum, Fusarium equiseti, Fusarium oxysporum, Fusarium solani and Nectria sp. dominated the surface-fertilized soil, and their activity in producing N2O was confirmed. These results suggested that N2O emission after the surface application of granular organic fertilizers in the cropland field mainly resulted from fungal denitrification.

Population density and spatial pattern of sclerotia of Sclerotinia sclerotiorum in desert lettuce production fields

Soil population densities and spatial patterns of sclerotia produced by Sclerotinia sclerotiorum were determined in six commercial lettuce production fields with varying histories of lettuce drop in Yuma County, AZ. Each field was divided into eight approximate equal sections and in each section, a plot (10 × 20 m) was randomly selected for soil sampling. Soil cores were collected along both diagonals at 2 m intervals in each plot and sclerotia populations were determined by wet sieving. The average soil sclerotia population per plot ranged from 0.0 to 5.8/100 g soil. The highest and the lowest percent of individual soil samples with ≥ 1 sclerotia/100 g soil per plot were 63% and 7%, respectively. Three indices of dispersions – variance/mean, Morisita’s index and Lloyd’s index – calculated for each of the six fields indicated that sclerotia distributions were aggregated. However, in none of the fields could the sclerotia distributions be adequately described by the Poisson, negative binomial or Neyman type A distributions.

Analysis of U.S. soil lead (Pb) studies from 1970 to 2012

Although lead (Pb) emissions to the air have substantially decreased in the United States since the phase-out of leaded gasoline by 1995, amounts of lead in some soils remain elevated. Lead concentrations in residential and recreational soils are of concern because health effects have been associated with Pb exposure. Elevated soil Pb is especially harmful to young children due to their higher likelihood of soil ingestion. The purpose of this study is to create a comprehensive compilation of U.S. soil Pb data published from 1970 through 2012 as well as to analyze the collected data to reveal spatial and/or temporal soil Pb trends in the U.S. over the past 40years. A total of 84 soil Pb studies across 62 U.S. cities were evaluated. Median soil Pb values from the studies were analyzed with respect to year of sampling, residential location type (e.g., urban, suburban), and population density. In aggregate, there was no statistically significant correlation between year and median soil Pb; however, within single cities, soil Pb generally declined over time. Our analysis shows that soil Pb quantities in city centers were generally highest and declined towards the suburbs and exurbs of the city. In addition, there was a statistically significant, positive relationship between median soil Pb and population density. In general, the trends examined here align with previously reported conclusions that soil Pb levels are higher in larger urban areas and Pb tends to remain in soil for long periods of time.

Spatial targeting of land rehabilitation: a relational analysis of cropland productivity decline in arid Uzbekistan

Irrigated croplands of Central Asia are highly prone to land degradation due to their fragile physical settings and extensive agricultural land use. Current remote-sensing data and spatio-temporal analyses allow for detecting regional trends in a land decline and for relating them to underlying factors which is important for developing mitigation strategies. This study aimed to (1) assess the cropland’s state in the large irrigated agricultural areas in the northern Uzbekistan based on the time series of MODIS NDVI images, (2) relate the degradation trend to its factors including soil quality, terrain, population density and land use, and (3) synthesize the results to provide recommendation on spatial targeting of land rehabilitation measures. An NDVI-based land degradation assessment revealed a significant decline of land productivity across 23.13% (94834.90 ha) of the arable area in the study region. The degraded cropland, located in the areas of high population pressure and characterized by better-quality soils, should be prioritized for rehabilitation measures. For the degraded cropland, found on the poor-quality soils and in the areas of low population density, depending on the severity of degradation, a decision has to be made whether to vacant the land from agriculture or to continue cultivation if the latter is an economically viable option.

Seasonal dynamics, slope aspect and land use effects on soil mesofauna density in the mid-hills of Nepal

This study addressed the integrated effects of season, slope aspect and land use on faunal population density, diversity and Soil Biological Quality (QBS-ar index) in the mid-hills of the central Nepal Himalaya. It also examined the relationship among these soil quality indicators. Faunal density and QBS-ar were significantly higher during the post-monsoon season when compared with the pre-monsoon season. Faunal population density during both the seasons was higher on the northern rather than southern slope aspects. Faunal density was significantly higher in the forest when compared with agricultural land in both the seasons. Soil moisture was positively correlated with soil organic carbon (SOC) and population density, but negatively correlated with soil temperature during the pre-monsoon period. In the post-monsoon season, bulk density was negatively correlated with QBS-ar and population density. Season, slope aspect and land use all had significant effects on the soil quality indicators. This study suggests that high SOC, moisture content and low bulk density lead to increases in population density of soil mesofauna and the QBS-ar index. Therefore, management practices that enhance SOC contents through plant residue retention on farm land, such as farmyard manure application, crop residue mulching and reduced tillage, could increase the numbers and diversity of soil organisms while improving the fertility and productivity of the land.