Soil Structural Index Research Articles

Effects of biochar application combined with nitrogen fertilizer on soil physicochemical pro-perties and winter wheat yield in the typical ancient region of Yellow River, China

The aims of this study were to reveal the effects of biochar application combined with nitrogen fertilizer on soil physicochemical properties and crop yield in the typical ancient region of Yellow River, and to clarify the dynamics of carbon and nitrogen content and soil physicochemical properties with different treatments of biochar and nitrogen, which could provide scientific basis for reasonable fertilization of soil, quality improvement of cultivated land, and yield increase of winter wheat. A two-year field experiment was conducted with different biochar applications (0, 15, 30 t·hm-2) combined with different nitrogen levels (N 270, 330 kg·hm-2) to investigate their effects on soil physicochemical property in the typical ancient of Yellow River. After 2-yr biochar application, the generalized soil structure index (GSSI) was increased and three-phase structure distance index of soil (STPSD) was decreased, and three-phase ratio was significantly improved. The most ideal state of three-phase ratio was in the condition of 30 t·hm-2 biochar application. Soil compactness and bulk density was decreased, total porosity and capillary porosity was increased, water holding capacity was improved, water and gas permeability was enhanced, and soil hardening was relieved. The composition of soil aggregate was also changed. Soil aggregate >0.25 mm particle size was increased by 70.6%-94.4%, and mean weight diameter (MWD) was improved by 24.0%-48.0%. Biochar application significantly increased organic carbon content by 15.8%-67.0%, adjusted soil C/N, reduced nitrogen release intensity, improved utilization rate of nitrogen fertili-zer, and enhanced soil fertility. However, it didn't increase soil pH. Soil pH showed a significant downward in 10-20 cm layer. With the same amount of nitrogen application, biochar application significantly increased average yield of winter wheat by 9.6%-25.6% in two years. With the same amount of biochar application, average yield of winter wheat with high nitrogen application was 2.5%-4.4% higher than that with conventional nitrogen application. In summary, combined biochar and nitrogen application could improve soil micro-environment, soil fertility and crop yield. Comprehensively considering soil modification, crop yield improvement and input cost, the optimum amount of fertilization was biochar application (30 t·hm-2) combined with nitrogen fertilizer (330 kg·hm-2).

Response of soil OC, N and P to land-use change and erosion in the black soil region of the Northeast China

Converting forest to cropland generally results in the deterioration of soil structure and the loss of soil organic carbon (OC) and nutrients, while agricultural soil erosion accelerates such degradation. To understand how soil structure, OC and nutrients respond to the conversion of forest to cropland and agricultural erosion, we compared soils between forest and cropland that was established in forest 60 years ago, and among croplands suffering various intensities of erosion (from non-erosion to heavy erosion). Soil samples were collected from 0−70 cm depth for the measurement of bulk density, OC, nitrogen (N) and phosphorous (P). The soil structural stability index was calculated. We showed that the conversion of forest to cropland decreased the soil structural stability and the concentrations and stocks of OC and N in the top 30 cm soils but had no effects on P. Soil erosion significantly increased soil bulk density but decreased soil structural stability and the concentrations and stocks of OC, N and P along the 0−70 cm soil profile. Additionally, most of the effects of erosion were enhanced with the intensity of erosion. However, OC, N and P were significantly higher at the deposition sites than at the either non-erosion or eroding sites in 15−70 cm soils, probably due to the burial of OC, N and P in deep soils of deposition sites. Moreover, the effects of converting forest to cropland on OC and N were greater than the effects of light erosion but smaller than the effects of moderate and heavy erosion in the top 30 cm soils. Therefore, erosion intensity should be carefully considered when disentangling the effects of converting natural ecosystem to managed ecosystem and soil erosion.

Polyacrylamide dissolved in low-quality water effects on structure stability of soils varying in texture and clay type

ABSTRACT Efficacy of polyacrylamide (PAM), a water-soluble soil conditioner, prepared with poor-quality water (low salinity, higher sodicity) commonly available to farm managers, is unknown. We studied the effects of treating aggregates of four soils with predominant smectitic or kaolinitic clay mineralogy with PAM solution prepared with poor-quality water (low salinity and high sodicity). Impact of PAM on pore size distribution (PSD) and structure stability of the soils and the relations between the stability indices obtained were studied from water retention curves derived at low suction (0–50 hPa). The retention curves were characterized by a modified van Genuchten model that yields (i) the model parameters α and n and (ii) a soil structure index (SI). Applying PAM modified the water retention curve shape, mostly in the smectite soils, and increased α and improved SI up to 3.3 and 1.7 times in the smectitic and kaolinitic soils, respectively, relative to the control. An observed exponential relationship between soil SI and parameter ɑ allowed predicting the effects of PAM addition on soil structure stability. The noted improvement in structure stability was comparable with results for conditions where PAM solution was prepared with good-quality water. Abbreviations: PAM, polyacrylamide; SAR, sodium adsorption ratio; EC, electrical conductivity; HEMC, high-energy moisture characteristic; VDP, volume of drainable pores; MS, modal suction; SI, structural index; PSD, pore size distribution.

Soil structure indices under different tillage systems of sandy loam soil in Hadejia, Jigawa state, Nigeria

Abstract. Soil structural indices have a significant effect on the nutrients retention and crop yield. Studies on soil structure indices in the semi-arid zone are minimal despite their importance in controlling water and water transmission, root elongation and erosion. A study was conducted in the area of Hadejia to evaluate the influence of tillage systems (TS) and sampling depths on some selected soil structure indices. The TS were four (4); conventional tillage (CT), reduced tillage (RT), zero tillage (ZT) and chisel plough (CP), while the sampling depths were two – 0-15cm and 15-30cm. Randomised complete block design (RCBD) was used in factorial arrangement. The result showed that the soil is sandy loam in texture irrespective of the TS. Lower dispersion ratio (DR) was observed in ZT with greater aggregate silt + clay (ASC) and water stability index (WSI) which differed significantly (p<0.01) from one another. Pearson’s correlation and simple linear regression analysis revealed a significant (p<0.01) positive and negative relationships between organic matter (OM) content of the soil with ASC, WSI and DR, respectively. Negative correlation of OM with DR stressed the significance of OM in decreasing DR of the soil which further explains lower DR by ZT because of greater OM content (p<0.05). Sodium (Na), sodium absorption ratio (SAR) and exchangeable sodium percentage (ESP) were in the order of RT>ZT>CT>CP with RT having the highest that differed significantly (p<0.05) from other TS. Lower values in CT and CP could be a result of leaching due to the lower surface residues relative to conservational tillage systems. Conclusively, the best tillage systems to improved soil structural indices are conservation tillage (ZT and RT) systems, particularly ZT.

Aluminium and iron oxides affect the soil structure in a long-term mineral fertilised soil

The influence of iron and aluminium (hydr)oxide on soil aggregation is still not sufficiently understood. Therefore, we undertook a study on the effects of Al and Fe forms on soil structure and their mutual relationships in sandy soil under long-term fertilisation experiments near Skierniewice (Poland). In this study, we examined three treatments of soil under long-term fertilisation: in 94- and 41-year- experiments: (1) control—without mineral fertilisation (Co); (2) mineral fertilisation (NPK); (3) mineral fertilisation + calcium (CaNPK). Treatments in the 25-year experiment included the following: (1) farmyard manure and no mineral fertilisation (FYM); (2) farmyard manure + mineral fertilisation (FYM + NPK); (3) farmyard manure + mineral fertilisation with calcium (FYM + CaNPK). We analysed parameters of soil structure such as dry-sieved aggregate and water-stable aggregate contents as well as calculating soil structure indices. Total contents of Al and Fe and their free oxides were determined. The results showed that in 94-year experiment, for NPK and CaNPK treatments, the content of dry-sieved macro-aggregates (DSAma) in the 5–3- and 3–1-mm size classes was significantly higher by 144 and 192% as well as by 37 and 36%, respectively, compared with that in the Co treatment. In comparison with the control, a lower percentage of macro-aggregate destruction (by 50%) and crusting index (Ic) (by 16%) was seen during the treatment with NPK fertilisation with added Ca. In the 41-year experiment, the structure coefficient significantly decreased after NPK and CaNPK fertilisation. In the 25-year experiment, the mineral fertilisation in combination with FYM did not affect individual size classes of DSAma. Values of Ic significantly decreased after the application of FYM in both NPK and CaNPK treatments. Overall, the highest number of correlations between Al and Fe free oxides and the soil structure was in the 94-year experiment, followed by the 25-year experiment, and the lowest number of significant correlations was in the 41-year experiment. Fe and Al oxides might act as important agents for stabilising mainly the higher size classes of DSAma. On the other hand, Fe, Al and their oxides did not have effect on the smaller size classes of DSAma, particularly in the 94-year experiment. Overall, the application of mineral fertilisers with farmyard manure could accelerate the positive changes in the structure of sandy soil, even, in particular, through Fe oxides.

Stacking Agricultural Management Tactics to Promote Improvements in Soil Structure and Microbial Activities

Linking agricultural management tactics to quantifiable changes in soil health-related properties is a key objective for increasing adoption of the most favorable management practices. We used two long-term, no-till cropping studies to illustrate the variable patterns of response of soil structure indices and microbial activity to additional management tactics, including crop rotational diversity, residue management and cover cropping. We found that observable effects of management tactics on soil properties were often dependent on the current crop phase sampled, even though the treatments were well-established. In some cases, a single additional management tactic produced a response, two tactics each produced a response and sometimes there were interactions between tactics. However, importantly, we never observed a negative effect for any of the response variables when stacking soil health building practices in no-till cropping systems. The collective results from the two field studies illustrate that soil health improvements with stacking management tactics are not always simply additive and are affected by temporal relationships inherent to the treatments. We conclude that the implementation of multiple positive management tactics increases the likelihood that improvements in soil properties can be documented with one or more of the proxy measures for soil health.

Soil Carbon Stock under Different Agro-climatic Zones and its Economic Valuation for Productivity Enhancement of Pigeon Pea (Cajanus cajan) in Southern Deccan Plateau

Soil Carbon (SC) storage is a key indicator of soil function used to monitor and predict crop response to management decisions. Under the SUJALA-3 Watershed Development Project, a total of 202 soil series representing major pigeon pea-growing soils were studied in seven agro-climatic zones of Karnataka. The organic and inorganic carbon stocks status were estimated at different soil depths to arrive at the economic value and assessed its relation with crop production. The SOC and SIC stock was 23.8 and 11.2 t ha-1 at 0-30 cm, 42.0 and 32.1 t ha-1 at 30-100 cm and 66.9 and 42.8 t ha-1 at 0-100 cm depth, respectively. The yield of pigeon pea was high (12.18 q ha-1) under high OC status of clay textured soils followed by medium SOC (11.11q ha-1) and low OC soils (11.52 q ha-1) in NETZ region. Using the agglomeration method, five groups were derived to determine the soil organic carbon management clusters. The soil organic carbon deficit (t ha-1) calculated to arrive investment requirement showed the order of cluster-4>cluster-3>cluster-1>cluster-5>cluster-2 and the investment required to bridge the gap of Rs. 30228, 26508, 26190, 22674 and 21990, respectively. As soil structure stability has an important role in carbon sequestration, the polynomial equation was constructed between soil carbon density and soil structural stability index, which yielded a threshold soil carbon stock value of 66.6 t ha-1 to attain a stable soil structure index value of nine. The ANOVA analysis showed statistically significant differences in SOC stock between regions (p = 0.022) and soil subgroups (p = 0.001). The study concludes an average investment of ₹ 25,000 ha-1yr-1 for 20 yr is required for enhancing the soil carbon status in Karnataka and to achieve the Pigeon pea potential yield of 20 q ha-1

QUALIDADE DA ESTRUTURA DO SOLO EM SISTEMA INTEGRADO DE PRODUÇÃO AGROPECUÁRIA NO MUNICÍPIO DE ARIQUEMES, RONDÔNIA

Objetivou-se avaliar a qualidade da estrutura do solo, em um sistema integrado de produção agropecuária. O estudo foi realizado na fazenda Esperança, no município de Ariquemes-RO, em agosto de 2017. Foram amostradas três áreas pertencentes ao sistema integrado de produção e uma área de pastagem extensiva. A área 1 apresenta antecedentes de cultivo em sucessão de milho/ Brachiaria ruziziensis (sem pastejo) no ano agrícola 2015/2016 e uma safra de soja em 2016/2017. Na área 2 anteriormente ocorreu o cultivo em sucessão de soja/milho/Brachiaria ruziziensis (com pastejo) no ano agrícola 2014/2015 com 1 safra de soja em 2015/2016 e novamente soja em 2016/2017. A área 3 é proveniente de sucessão Brachiaria ruziziensis/soja (sem pastejo) no ano agrícola de 2014/2015, seguida de 1 safra de soja em 2015/2016 e novamente soja/Brachiaria ruziziensis em 2016/2017. A área 4, era constituída de uma pastagem degradada. Avaliou-se a qualidade da estrutura do solo visualmente, pelo método de diagnóstico rápido da estrutura do solo, atribuindo notas de 1 a 6 para o Índice de qualidade estrutural do solo (IQES). Os manejos empregados nas áreas 1, 2 e 3 proporcionaram a obtenção de qualidade estrutural do solo superior a da área 4 (área de pastagem degradada), sendo observadas as seguintes notas 4,87; 4,67; 5,67 e 2,57, para as áreas 1, 2, 3 e 4, respectivamente. A Sucessão Brachiaria ruziziensis/soja (sem pastejo), soja, soja/Brachiaria ruziziensis resultou em melhor qualidade da estrutura do solo. A pastagem degradada apresentou qualidade da estrutura do solo ruim. PALAVRAS-CHAVE: Estrutura do solo, Manejo do solo, Plantio direto.

SOIL STRUCTURAL QUALITY AS A FUNCTION OF MANAGEMENT IN AN INTEGRATED AGRICULTURAL PRODUCTION SYSTEM

O objetivo do trabalho foi avaliar a qualidade estrutural do solo, em função do manejo, em um SIPA no município de Rio Crespo-RO. O estudo foi realizado na fazenda Esperança, em setembro de 2017. Foram estudados os seguintes manejos: área 1: safra-milho-grao/safrinha-soja (2015/2016); safra-soja/Bracharia ruzizienses/pastejo-60 dias - 3,87 UA/ha (2015/2016); safra-soja/safrinha-milho-silagem/Bracharia ruzizienses pastejo-60 dias - 3,39 UA/ha (2016/2017); área 2: safra-milho-grao/safrinha-soja (2015/2016); safra-soja/Bracharia ruzizienses/pastejo-60 dias - 3,39 UA/ha (2015/2016); safra-soja/safrinha-milho-silagem/Bracharia ruzizienses - pastejo-60 dias - 4,22 UA/ha (2016/2017); área 3: crotalária/safra-milho-grao/safrinha-soja (2015/2016); safra-milho-grao (2015/2016); safra-soja/safrinha-milho-grão / Bracharia ruzizienses sem pastejo, área 4: crotalária/safra-milho-grao/safrinha-soja (2015/2016); safra-milho-grao /Bracharia ruzizienses/pastejo-60 dias - 3,20 UA/ha (2015/2016); safra-soja/safrinha-milho-grão/Bracharia ruzizienses - pastejo-60 dias - 4,22 UA/ha (2016/2017) e área 5: mata nativa. A avaliação da qualidade do solo foi feita visualmente pelo método de diagnóstico rápido da estrutura do solo, com atribuição de notas para o Índice de qualidade estrutural do solo (IQES) de 1 a 6. O IQES de cada área foram: área 1 - 5,67 (qualidade estrutural muito boa); área 1 e 4 com IQES de 4,12 e 4,05, respectivamente (qualidade estrutural boa). As áreas 2 e 5 com IQES de 2,77 e 2,54 respectivamente (qualidade estrutural ruim). A implantação de SIPAs resulta em melhoria na qualidade estrutural do solo. A melhor qualidade da estrutura do solo é obtida quando não se emprega pastejo animal. Em áreas com lotação animal maior que 4,0 UA/ha é necessário monitoramento constante da qualidade da estrutura do solo, observando também a distribuição homogênea dos animais na área.PALAVRAS-CHAVE: Estrutura do solo, Integração-lavoura-pecuária, Manejo conservacionista.

Effects of land-use change on Nitisols properties in a tropical climate

El cambio en el uso de la tierra, especialmente la conversión de bosques nativos en tierras cultivadas ejerce un impacto sobre las propiedades físicas, químicas e hidrofísicas de los suelos. El objetivo de este estudio fue evaluar la influencia de diferentes sistemas de manejo de un suelo tropical reflejado en algunas de sus propiedades físicas, químicas e hidrofísicas. Se evaluaron nueve perfiles de un suelo Nitisol agrupado en tres categorías: (I) bosque nativo (Referencia > 30 años); (II) suelos anteriormente cultivados y luego convertidos en pastizales (Conservados > 10 años); y (III) suelos bajo cultivo continuado (Agrogénicos > 50 años). Las variables analizadas fueron materia orgánica, densidad aparente, densidad real, porosidad, capacidad de campo, textura e índice estructural. Los resultados determinaron que la acción de las técnicas agrícolas tradicionales en ambientes tropicales produce una excesiva degradación de las propiedades del suelo. El contenido de materia orgánica e índice estructural muestran una relación lineal con un alto grado de dependencia (R2=0,99). La densidad aparente promedio para los perfiles (I) y (II) fue menor (P<0,05) que los valores de densidad aparente del perfil (III). En los análisis de regresión a medida que aumenta la densidad aparente disminuye la capacidad de campo y la tendencia observada para (I) y (II) es lineal, mientras que para (III) es polinómica con (R2=0,83), pudiendo estar influenciado por los valores más altos de la densidad aparente, mayor compactación, menor índice estructural, materia orgánica y porosidad en correspondencia con los otros perfiles.

Soil structural quality in pasturelands in the city of Buritis (RO), Brazil

Thisstudy aims to evaluate the soil structural quality of pasturelands in the city of Buritis (RO), Brazil. The analysis took place at Boa Esperança and Boa Sorte farms, in November 2017. Three areas at Boa Esperança were evaluated: 1 –cultivation of Panicum maximum cv. Mombaça planted for 19 years; 2 –cultivation of Panicum maximum cv. Mombaça planted for two years; and 3 –cultivation of Brachiaria brizantha cv. Xaraés planted for a year and a half. The area 4 was evaluated at Boa Sorte, having Brachiariadecumbens cultivated for two years. For structural evaluation purposes, the visual examination method was deployed and grades from 1 to 6 for Soil Structural Quality Index were attributed. The average of indexes in each area was: area 1 –4,87 (good structural quality); area 2 –3,64 (regular structural quality); area 3 –4,67 (good structural quality); and area 4 –3,36 (regular structural quality). The obtained grades for areas 2 and 4 show that land use in such areas should be treated with conservationist techniques to improve overall soil structural quality over time. The good quality shown in area 1 points out that keeping fodder plants for large periods of time does not compromise overall structural quality. In this scenario, for better production results, it is only needed to improve chemical factors by fertilizing and correcting soil acid levels. The evaluation of soil structural quality is proven to be useful to help producers enhance their methods of land use, also contributing to a sustainable livestock production.

Clay activity index as an indicator of soil erodibility

Activity index (AI) value characterizes the relationship between the plasticity index and clay content. In this study, AI value was investigated to determine whether it might be used as an indicator of soil structural stability or not. The AI values of 75 soil samples gave the significant negative correlations with their dispersion ratio (DR), soil erodibility factors (K) and erosion ratios (ER). Also, the AI values of the soils including clay and sandy clay loam textural class showed significant positive correlation with soil structural stability index (SSI). It seems that the AI value may be used as an indicator of soil structural stability.

Soil water retention, air flow and pore structure characteristics after corn cob biochar application to a tropical sandy loam

Soil structure is a key soil physical property that affects soil water balance, gas transport, plant growth and development, and ultimately plant yield. Biochar has received global recognition as a soil amendment with the potential to ameliorate the structure of degraded soils. We investigated how corn cob biochar contributed to changes in soil water retention, air flow by convection and diffusion, and derived soil structure indices in a tropical sandy loam. Intact soil cores were taken from a field experiment that had plots without biochar (CT), and plots each with 10tha−1 (BC-10), 20tha−1 without or with phosphate fertilizer (BC-20 and BC-20+P respectively). Soil water retention was measured within a pF range of 1 to 6.8. Gas transport parameters (air permeability, ka, and relative gas diffusivity, Dp/D0) were measured between pF 1.5 and 3.0. Application of 20tha−1 led to significant increase in soil water retention compared to the CT and BC-10 as a result of increased microporosity (pores <3μm) whereas for soil specific surface area, biochar had minimal impact. No significant influence of biochar was observed for ka and Dp/D0 for the BC treatments compared to the CT despite the larger values for the two properties in the 20tha−1 treatments. Although not significant, the diffusion percolation threshold reduced by 34% and 18% in the BC-20 and BC-20+P treatments, respectively, compared to the CT. Similarly, biochar application reduced the convection percolation threshold by 15 to 85% in the BC-amended soils. The moderate impact of corn cob biochar on soil water retention, and minimal improvements in convective and diffusive gas transport provides an avenue for an environmentally friendly disposal of crop residues, particularly for corn cobs, and structural improvement in tropical sandy loams.

Challenges of conservation agriculture practices on silty soils. Effects on soil pore and gas transport characteristics in North-eastern Italy

Soil air exchange is one of the most important soil functions that directly impacts on crop productivity and environment. Generally, conservation agriculture (CA) practices are expected to provide improved soil aeration but contrasting texture-related effects were found in the literature. The aim of this study was to evaluate the effect of CA practices on gas transport characteristics in the silty soils of the Veneto Region (North-Eastern Italy). In 2010, a field experiment comparing CA practices (no-tillage, cover crop and residues retention) to conventional intensive tillage (IT) system was established in four farms located in the Veneto low plain. In fall 2015, 144 undisturbed 100cm3 soil cores where collected at two different layers (3–6.5cm and 20–23.5cm) and analysed for air-filled porosity, air permeability, gas diffusivity and soil structure indices derived.Gas transport measurements highlighted low transmission properties of the silty soils independently from agronomic management. Both air permeability and relative gas diffusivity showed poor aerated conditions being generally <20μm2 and <0.005, respectively.CA treatments affected the transmission properties only in the coarsest soil studied causing a reduction of air permeability in the deeper layer and relative gas diffusivity in both layers. The CA-induced reduction was related to the tillage effect on soil bulk density and suggested that CA not only affected the air-filled porosity but also continuity and tortuosity characteristics.The poor structural stability of Veneto soils, particularly the poor soil organic carbon content, could prevent the exploitation of CA practices firstly on soil structure and in turn on gas exchanges. For these reasons further studies elucidating the mechanisms improving soil structural conditions for silty soils as those examined in this study are required.

Effect of vegetation type on microstructure of soil aggregates on the Loess Plateau, China

Several types of vegetation restoration have been implemented on the Loess Plateau in China to control soil erosion and improve soil quality. Different revegetation types, however, have varying effects on soil structure; effects on the pore network of aggregates are especially not well understood. We used synchrotron-based high-resolution X-ray micro-computed tomography to quantify the microstructure of soil aggregates under four types of revegetation and an active cropland on the plateau. Five aggregates (3–5mm) collected from the topsoil at each site were scanned at a voxel resolution of 3.25μm, and the aggregate pore structure was visualized and quantified with ImageJ. Total porosities, >75μm porosities, fractions of elongated pores, 3D mass fractal dimensions, and connectivity were higher and the numbers of pores, <75μm porosities, the mean pore-shape factors, and the fractions of regular and irregular pores were lower in the revegetated sites than the control plot. Total porosities, macro-porosities, micro-porosities, fractions of regular pores, and 3D mass fractal dimensions differed significantly among the revegetated sites. We suggest that the fraction of elongated pores can be used as an important indicator for monitoring the recovery of soil structure. 3D mass fractal dimensions differed more than connectivity in the aggregates in the same samples, and thus could be a more sensitive indicator of changes in the pore network. Age and revegetation type both significantly affected the development of soil structure, but revegetation type was more important for the recovery of soil structure. We used a soil structural index (SSI) obtained by principal component analysis to assess the overall quality of soil structure. SSI values were higher in all revegetated sites than the cropland site and differed among the revegetated sites in the order: shrubland>grassland>woodland>pastureland. We recommend shrub plantation and natural grassland for the revegetation of degraded land on the Loess Plateau.

Relationship between soil water retention model parameters and structure stability

Studying and modeling the effects of soil properties and management on soil structure and near saturation water retention is vital for the development of effective soil and water conservation practices. The contribution of soil intrinsic properties and extrinsic conditions to structure stability was inferred, in quantitative terms, from changes in water retention curves near saturation (low matric potential, 0-50 cm, macropores > 60 µm) that were obtained by the high energy moisture characteristic (HEMC) method. The S-shaped water retention curves were characterized by the modified van Genuchten model that provided: (i) the model parameters α and n, which represent the location of the inflection point and the steepness of the water retention curve, respectively; and (ii) the soil structure index, SI=VDP/MS, where VDP is the volume of drainable pores, and MS is the modal suction. Model parameters, claculated by the soil-HEMC model, were related to soil properties and hence soil water retention properties were linked to measured characteristics in several field and laboratory experiments. Soil SI increased exponentially with the increase in α and the decrease in n, while the relationship between SI and α/n was linear. An improved description of the water retention and its link to pore and apparent aggregate size distribution, by using the model parameters α and n, could potentially assist in the selection of management practices for obtaining the most suitable type of soil structure depending on the desired soil function.

Tidal Suppression Negatively Affects Soil Properties and Productivity of Spartina densiflora Salt Marsh

In order to intensify cattle utilization, embankments were constructed to avoid tidal ingressions in Samborombon Bay, Argentina, The objective of this study was to evaluate the effect of tidal suppression and cutting frequency of a salt marsh dominated by Spartina densiflora Brongn. Two paddocks of a commercial cow-calf operation farm, one prevented from tidal flooding and another exposed to overflow from natural tidal pattern (control), were the main plots of the nested design. The experiments were carried out during a dry (2008- 2009) and a wet growing season (2012-2013). Two defoliation frequencies, simulating light and moderate grazing pressure, were performed in the subplots nested within each main plot. Soil organic matter and N content were lower and soil structural instability index was much higher in the embankment than in the control treatment. Soil salinity during the dry growing season was higher in the embankment than in the control treatment. Bare soil was higher under embankment treatment and high defoliation frequency exacerbated this response. Relative contribution of Spartina densiflora was lower under embankment than control treatment and the changes of floristic composition depended on the growing season. Aboveground net primary production (ANPP) in the wet growing season was almost 70% higher than in the dry growing season. Embankment reduced ANPP and high defoliation increased ANPP with respect to low defoliation frequency in the control paddock, to a much higher extent in the wet season. Dry matter digestibility of S. densiflora was not affected by treatments. Crude protein was higher in control paddocks under high frequency. Our results showed that tidal suppression by embankment was not effective to increase productivity and forage value of S. densiflora saltmarsh but caused soil and structural changes that may negatively alter ecosystem processes of this vulnerable grassland of high importance for biodiversity conservation.

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto, Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100kgNha−1 for upland rice, and 0 and 20kgNha−1 for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.

Short-term effects of tillage practices on soil properties under Tef [Eragrostis tef (Zucc. Trotter)] crop in northern Ethiopia

Tef crop shares the largest area of production in Ethiopia. However, its productivity is lower than 0.7tonha−1 which is mainly related to low soil fertility and moisture. An experiment was conducted using tef on Chromic Cambisols for two rainy cropping seasons (2008–2009) in northern Ethiopia. The objective was to assess the short-term effects of tillage frequencies on selected soil properties under continuous tef cropping system. The layout of the experiment was randomized complete block design using three tillage treatments, namely, conventional plowing (T1), four times plowing (T2), and reduced plowing (T3). A statistically significant (P≤0.05) effect of tillage treatments on soil moisture (SM) was determined during the experimental periods. SM was higher in T2 in both years followed by T3 in 2009. Soil physical properties (bulk density, BD; total porosity, TP; soil structural stability index, SSI) and soil nutrients (total nitrogen, TN; organic carbon, OC; cation exchange capacity, CEC; potassium, K) were significantly deteriorated by the application of T1 for consecutive two-years. The Paired-Samples T-Test showed significant improvements in these soil parameters due to T2 and T3 in 2009 as compared to the corresponded values in 2008. For example, there were significant increments in SM (11%), TP (18%), SSI (12%), TN (1.2 times), phosphorous (5%), OC (13%), and CEC (15%); but significantly decreased in OC: TN (48%) and BD (4%). Generally, despite the non-significant differences between the effects of T2 and T3, higher TP, SSI, OC, CEC; and lower BD were observed by T3 in 2009. Based on such short-term results of T3 it is possible to forecast its significant long-term effects on soil properties. Thus, for sustainable use of soil systems in the long-term due attention should be given to practice T3 as soil and water management practice in the study area conditions.

Land Use Impact on Soil Physical Quality and Soil Structure in Three Highland Watersheds of Ethiopia

Continuous monitoring of soil physical quality is essential in determining sustainability of land use in natural and managed ecosystems particularly; mountainous systems such as the Ethiopian highlands, where soil deterioration and degradation can become major threats to ecosystem and productivity. This study focused on assessment of soil physical quality (SPQ) by comparing values of soil indicator properties to their corresponding ‘ideal ranges’ established in literature and determining soil structural stability and aggregate associated carbon as influenced by land use types. It further employs factor analysis to identify appropriate SPQ indicators and soil structural indices that are dominantly influenced by each land use type in the three watersheds (namely; Jeldu, Diga and Fogera) of the Ethiopian highlands. Surface soil samples were collected from four adjacent agricultural land use types (namely; Grass fallow, Tree fallow, Homestead and Continuous field cropping) within each of the three watersheds for study of Dexter “S” index, aggregate associated carbon and aggregate stability and other SPQ indicators. Results revealed that soils were only adequate in Relative Field Capacity and Plant Available Water Capacity in all watersheds. The soils of the watersheds still maintained good physical quality but there are strong indications of low soil structural resilience and tendency to degrade. Factor analysis grouped SPQ indicators and structural indices into three factors: (Factor 1) structural stability (with soil organic carbon, aggregate associated organic carbon and aggregate size being the most dominant soil quality indicators); no dominant attribute for Factor 2 and Factor 3 is mainly soil texture (with clay being the most dominant). Soil improvement programme in the watersheds lies in management practices that will promote proper management of organic carbon as it is the principal SPQ indicator that influenced variation in other soil attributes.