Agricultural Soil Fertility Research Articles

Fertilizer regime changes the competitive uptake of organic nitrogen by wheat and soil microorganisms: An in-situ uptake test using 13C, 15N labelling, and 13C-PLFA analysis

Fertilizer regime affects plant growth and soil microbial community composition, however, its impact on organic nitrogen (N) uptake by plants remains poorly understood. To address this, we undertook an in-situ, short-term uptake experiment based on 13C, 15N labelling, and 13C-PLFA analysis at two long-term (6 year) fertilizer trial sites (Jintan and Changshu). Each site had five treatments: a control without fertilizers, NPK fertilizers, 50% NPK fertilizer +6 t/ha pig manure, 100% NPK fertilizer + cereal straw, and 50% NPK fertilizer +6 t/ha pig manure and cereal straw. Overall, we found that 6–21% and 6–11% of the added 13C-15N-glycine was taken up intact by wheat, while 18–35% and 8–20% was captured by soil microorganisms in Jintan and Changshu locations, respectively. These results indicate that wheat has an appreciable capacity to utilize organic N, even in fertile agricultural soils. Organic N uptake by wheat correlated positively with ammonium and nitrate soil contents, indicating that inorganic N may enhance organic N capture by increasing plant biomass. The 13C:15N ratio in the microbial biomass showed that 32–71% and 13–71% of the 15N was absorbed through a direct uptake route in Jintan and Changshu soils. Chemical fertilizer reduced microbial biomass and increased the proportion of intact glycine uptake by wheat. Gram-positive bacteria accounted for 18–23%, and 13–15% of the total 13C labelled PLFA in Jintan and Changshu, respectively, while Gram-negative bacteria accounted for 43–48% and 66–72% indicating that they are the dominant competitors with plants for soil nutrients. Total 15N uptake by wheat and microorganisms was highest in the 50% NPK fertilizer + pig manure and cereal straw treatment at both sites, indicating that it represents the best fertilizer practice for sustainable food production, as it not only reduced chemical fertilizer application, improved wheat growth and microbial biomass, but also increased wheat utilization of soil organic N.

Long-term benefits of combining chemical fertilizer and manure applications on crop yields and soil carbon and nitrogen stocks in North China Plain

Application of manure is reported to effectively improve agricultural soil fertility. However, the potential of annual manure applications to increase stocks of soil organic carbon (SOC) and total nitrogen (TN) needs to be better understood. In this study, we evaluated the long-term (1991–2012) effects of various fertilization regimes on crop yield, and SOC and TN in the topsoil (0–20 cm) of a fluvo-aquic soil in a wheat (Triticum aestivumL.)-maize (Zea mays L.) cropping system in the North China Plain. The treatments included no N fertilizer (PK), chemical N, P, K fertilizers (NPK), NPK plus 22.5 t ha−1 swine manure (NPKM), and NPK plus 33.75 t ha−1 swine manure (NPKM+). Compared with NPK and PK, both NPKM and NPKM+ significantly increased crop yields, with no significant difference between NPKM and NPKM+. NPKM and NPKM+ treatments had a lower N use efficiency (NUE) than NPK through the whole period and the average NUE were 30.1%, 14.8% and 12.3% in NPK, NPKM and NPKM+ treatments, respectively. Compared with the initial value of 17.2–17.4 Mg C ha−1 and 2.01–2.07 Mg N ha−1, SOC and TN stocks in NPKM and NPKM+ increased by 94.7–114.2% and 83.0–98.0% over the 22 experimental years, respectively, without any indication of C or N saturation in the soil. Furthermore, TN stock was positively correlated to SOC stock (P < 0.01) added with manure, indicating the significance of more organic C input from manure to build up TN pool. In conclusion, long-term application of organic manure in combination with conventional chemical fertilization could increase crop yield and soil C and N stocks in the wheat-maize cropping system of the North China Plain, but it should be noted that large amounts of manure N could also lead to elevated risk of environmental N losses.

Assessment of soil fertility index for potato production using integrated Fuzzy and AHP approaches, Northeast of Iran

Considering the important role of soil fertility and nutrient management in the modern agriculture seems to be a key step in appropriate site-specific fertilizers management for crop production. The present study was conducted to prepare a soil fertility zonation map based on soil nutrient elements including total nitrogen, available potassium and phosphorus, magnesium, manganese and iron and soil chemical parameters comprising cation exchange capacity, organic carbon, salinity and pH by integrated Fuzzy and AHP approaches for potato production in Rokh plain, northeast of Iran. In this regard the most important soil chemical parameters and nutrient elements in 0-30 cm depth of the soil was analyzed and mapped. The S-shaped fuzzy membership function was subsequently defined for each factor to fuzzify soil fertility parameters. The soil fertility map was prepared by weighing factor layers by the AHP approach and summation of factor layers by IDW interpolation function in GIS. The values of the soil fertility index in the scale of 0 to 1 ranged from 0.104 to 0.574, classified the study area in very low (922.90 km 2 ), low (566.10 km 2 ) and moderate fertility (14.86 km 2 ) classes which comprises 61.37%, 37.64% and 0.99% of the surface area, respectively. A regression between soil fertility values and potato yield in the study area revealed a high correlation (R 2 = 0.91) between the observed results which validate the zonation of the fertility classes in the region.

Ayçiçeği Bitki Artıklarının Organik Tarım Amaçlı Değerlendirilmesi

İnsan beslenmesinde önemli bir yere sahip olan tarımsal ürünlerin yetiştiriciliğinde kullanılan hormon, ilaç, gübre gibi kimyasal girdiler sağlığı olumsuz yönde etkilemektedir. Bu nedenle günümüzde, toprağa ve bitkiye zarar veren kimyasal maddeler yerine bitkilerin ihtiyacı olan ve insan sağlığını olumsuz yönde etkilemeyen organik gübre ve doğal ilaçlama yöntemleri geliştirilmeye çalışılmaktadır. Organik tarım, insanların sağlıklı beslenmesinin yanı sıra toprak verimliliğini artıracak her türlü organik artıkların değerlendirilmesi ve tarımda devamlılığın sağlanması açısından büyük önem arz etmektedir. Özellikle ayçiçeği bitkisinin tüm kısımlarında %63,9 potasyum (K2O), %21,7 azot (N) ve %14,4 fosfor (P2O5) besin elementleri bulunduğundan, ayçiçeği yetiştiriciliği yapılan yerlerde hasat sonrası arazide kalan belirli miktarda sap ve köklerin toprağa karıştırılarak yeşil gübre olarak kullanılması pratikte uygulanabilecek en önemli yöntemlerden biridir. Ayrıca hasat sonrası geriye kalan sap, tabla gibi kısımlar, yakacak olarak değerlendirilirken, yanma sonucu elde edilen ve yüksek oranda potasyum bulunan külleri tarlaya serpilerek organik gübre olarak da değerlendirilebilmektedir. Bu derlemede; özellikle ülkemizde organik madde yönünden fakir olan araziler için bir kenara atılarak heba edilen ve çevre kirliliğine neden olan ayçiçeği hasat artıklarının organik hammadde olarak kullanılması, organik ürün elde edilmesi yönünde çiftçilerin bilinçlendirilmesi ve bu şekilde ülke ekonomisine sağlayabileceği konular ele alınmıştır.

Using multi-objective optimization to secure fertile soils across municipalities

To protect fertile agricultural land and guarantee food security in regions that are strongly affected by urban growth, it is crucial to use and design appropriate policy instruments. In Switzerland, as well as in many other countries worldwide, one of the most important instruments for steering urban development is zoning. Zoning regulations are usually implemented at local governance levels (i.e. at municipality level) and have proven to effectively account for externalities. To determine whether zoning across municipalities could lead to a better protection of fertile agricultural soils, we developed an innovative approach based on multi-objective optimization. Using this approach we quantified the trade-off between reducing the loss of agricultural productivity and obtaining compact urban development patterns. We show that cooperation between municipalities is useful at two different stages in the decision-making process. Firstly, municipalities should cooperate when they define their environmental and socio-economic development goals and rank their preferences concerning different goals. Secondly, municipalities should cooperate when deciding on how much agricultural land should be converted into urban land. These results allow decision-makers to understand if zoning at a supra-municipal level significantly reduces the loss of agricultural productivity and should thus be favoured over zoning at the municipal level.

Impact of rice-husk ash on the soil biophysical and agronomic parameters of wheat crop under a dry tropical ecosystem

Abstract Several alternative amendments like organic manure and biochar have been proposed for revitalizing the degrading soil viability and fertility for sustainable agriculture, globally. However, detailed field-scale studies focussing on the soil and agronomic parameters of crops under these amendments are limited in dry tropical ecosystems. Therefore, we studied the impact of various soil amendments viz., rice-husk ash (RHA) and farm-yard manure (FYM) along with mineral fertilizer on soil biophysical and agronomic parameters of wheat crop. We specifically explored the impact of the amendments on soil CO2 efflux (SCE, under different growth stages) and the harvest index of wheat crop, which are considered as the key indicators of soil viability and agronomic efficiency, respectively. SCE, soil moisture, soil temperature, soil N, microbial biomass and soil pH were found significantly varying under different treatments (P

Effectiveness of the application of rice straw mulching strips in reducing runoff and soil loss: Laboratory soil flume experiments under simulated rainfall

The use of mulch as a management tool has shown one of the highest effectiveness/cost ratios for improving agricultural soil fertility, crop productivity, soil restoration in badlands and post-fire soil erosion mitigation. Some researchers have suggested that mulching costs can be reduced by applying it in strips rather than over the entire area. However, the implications of strip-wise mulching on the effectiveness to reduce soil erosion are poorly known. This study aimed to evaluate, in laboratory experiments, the effectiveness of strip-wise mulching with rice straw in reducing runoff and soil loss for a highly erodible sandy loam soil at a steep slope of 40%. Six mulching application schemes were compared against a bare soil. The six schemes combined two surface cover rates of 50 and 70% and three spatial patterns: mulch over the entire flume length and two strips of 1/3 and 2/3 of the flume length, both located at the bottom part of the flume. The runoff-erosion experiments involved the simulation of a sequence of three rainfall events, the latter one combining the application of concentrated flow from upslope of the soil flume. Overall, mulching was more effective in reducing soil loss than runoff (50 vs. 25%) and was significantly more effective during the first rainfall event than during the following two events (83 v. 16% for runoff and 92 vs. 53% for soil loss). During the third event, mulching effectiveness dropped significantly with increasing rates of upslope concentrated flow. Overall, mulching was more effective when applied over the entire flume length than over the 1/3 and 2/3 flume’s length strips, both in terms of runoff (24 vs. 21 and 13% at 50% soil cover and 41 vs. 33 and 16% at 70% soil cover) and of soil loss (44 vs. 50 and 33% at 50% soil cover and 71 vs. 60 and 39% at 70% soil cover). Even so, these differences were not significant. Therefore, strip-wise mulching can be an effective approach to substantially reduce costs or to maximize the area that can be treated. Its main disadvantage may be that it does not avoid runoff generation and associated transport process in the slope areas where no mulch is applied.

Can Strategic Spatial Planning Contribute to Land Degradation Reduction in Urban Regions? State of the Art and Future Research

Land degradation is becoming a serious environmental issue threatening fertile agricultural soils and other natural resources. There are many driving forces behind land degradation. The expansion of artificial surfaces due to various economic activities, such as housing, industry, and transport infrastructure, known as soil sealing, constitutes one of the most intensive forms of land degradation in urban regions. Measures to halt and reverse land degradation require both strong land-use management policies, as well as effective spatial planning mechanisms. In this regard, strategic spatial planning has been increasingly practised in many urban regions worldwide, as a means to achieve sustainable land-use patterns and to guide the location of development and physical infrastructures. It is reasonable, therefore, to expect that strategic spatial planning can counteract the outlined undesired land degradation effects, specifically those resulting from soil sealing. In this paper, we review strategic spatial planning literature published between 1992 and 2017. The focus is on the phenomena causing land degradation that are addressed by strategic spatial planning literature, as well as on the mechanisms describing the role of strategic spatial planning in land degradation reduction. Results show that sustainable development and environmental concerns have become core objectives of strategic planning in recent years, yet references to the drivers of land degradation are rare. The mechanisms that exist are mainly intended to address environmental issues in general, and are not aimed at reducing particular forms of land degradation. The paper concludes by sketching future research directions, intended to support strategic spatial planning and land-use policymaking related to coping with the global phenomenon of land degradation.

Potencial de cinco especies de leguminosas como abonos verdes en la zona altiplano de San Luis Potosí, México

Los abonos verdes (AV) son una alternativa para mejorar la fertilidad y conservación de suelos agrícolas en zonas semiáridas. Por tal motivo, se evaluó el potencial de cinco especies de leguminosas como AV en el altiplano de San Luis Potosí, México. Las especies de estudio fueron: 1) frijol dolichos negro (Lablab purpureos); 2) frijol dolichos café (Lablab purpureos); 3) frijol dolichos rojo (Lablab purpureos); 4) frijol yorimón (Vigna unguiculata); y 5) garbanzo (Cicer arietinum). El ensayo se realizó bajo un diseño de bloques al azar con tres repeticiones. En la etapa de floración de cada especie se realizó la evaluación. Las variables que se midieron fueron: biomasa, captura de carbono, huella de carbono, nitrógeno en planta y relación C/N. Los resultados indican que Dolichos rojo fue la más sobresaliente en producción de biomasa (6.5 t ha-1), captura de carbono (2.97 t ha-1) y huella de carbono (-4.3 t ha-1). Cicer arietinum sobresalió en concentrar N en sus tejidos (2.03, 1.47 y 1.87% en parte aérea, raíz y planta completa) y podría aportar al suelo hasta 83 kg ha-1 N. Cicer sp., tuvo la más baja relación C/N con 24.12, con lo que tendría una mineralización más rápida que las demás especies. Como conclusión, las cinco especies tienen potencial para usarse como AV en la zona de estudio y son una alternativa importante para mejorar los suelos agrícolas y el medio ambiente.&#x0D; &#x0D;

Improving strategies for sustainability of short-term agricultural utilization on degraded peatlands in Central Kalimantan

Indonesia is the major contributor of peatland areas in the tropics; however, exploitation of peatlands for various needs with improper management such as illegal logging activities, conversion to plantations, and expansion of smallholder agriculture has caused peatland degradation. In Central Kalimantan Province, only 1.5 million ha (57%) of the total 2.6 million ha peatland is categorized as pristine peatlands forest and the remaining 1.1 million ha is categorized as degraded. Degraded peatland is a significant source of CO2 emissions as well as one such alternative for agricultural expansion. There is scientifically unfounded belief that drained peatland agriculture can be made “long-term sustainable”; therefore, the main idea is only short-term utilization of degraded peatlands for agriculture in a relatively sustainable manner, while effort for conservation and reforestation for long-term sustainable keeps going on. Prospective structural analysis was used to identify the most influential and sensitive variables to be influenced for determining the locally most crucial areas of improvement for enabling short-term agricultural utilization of degraded peatlands in a relatively sustainable manner. This method is a part of strategic foresight toolbox for scenario building process, which observes interrelation and influence among different variables in order to understand the most relevant factors for the development of a specific area. Based on the analysis, the strategies considered for enabling short-term agricultural utilization of degraded peatlands in a relatively sustainable manner include improvement in soil fertility and suitability for agriculture, infrastructure related to peatlands agriculture, institutional capacity, innovation technology and dissemination, farmer knowledge in sustainable peatlands agriculture, and plant productivity. Agricultural expansion implemented in connection with these improvements would enhance the welfare of farmers as well as maintain ecological systems.

Long-term soil accumulation of potentially toxic elements and selected organic pollutants through application of recycled phosphorus fertilizers for organic farming conditions

The pollutant input and the risk of contamination by long-term application of recycled P fertilizers (RPFs) in European agricultural soils were estimated by a mass balance approach. Calculations based on literature data were carried out for the potentially toxic elements (PTEs) Cd, Cr, Cu, Ni, Pb, Zn and for the persistent organic pollutants (POPs) PCBs, PAHs and polychlorinated dibenzo-dioxins and -furans. The PTE accumulation estimation during 200 years of fertilizer application, equivalent to 11 kg P ha−1 year−1, the mean P export via harvested products on European stockless organic farms, regarded soil background concentrations and proposed threshold concentrations. For PTEs, inputs were fertilizer application, atmospheric deposition and liming, output processes were leaching and crop harvest. The effect of varying site conditions was assessed by considering two precipitation excess (F) values and two soil pH values. For POPs, fertilizer application and the half-life time were considered. The PTE accumulation risk was low for most RPFs. For the analysed POPs no accumulation was found. The highest accumulation was found for all PTEs at pH 7 and F = 0.1 m year−1, the lowest at pH 5 and F = 0.3 m year−1. A high P concentration in fertilizers resulted in a low PTE flow per unit of P. Composts had the highest PTE accumulation risk due to lowest P contents. Struvite, meat and bone meal, digestate of catering waste, ash and biosolids would be better suited as P fertilizers. The use of fertilizers should be regulated based on their pollutant-to-nutrient ratio.

Soil Fertility in Agriculture: Russia – Western Europe – USA: in the Past and Today

Soil Fertility in Agriculture: Russia – Western Europe – USA: in the Past and Today

“Green technology”: Bio-stimulation by an electric field for textile reactive dye contaminated agricultural soil

The aim of the study is to degrade pollutants as well as to increase the fertility of agricultural soil by starch enhancing electrokinetic (EKA) and electro-bio-stimulation (EBS) processes. Starch solution was used as an anolyte and voltage gradient was about 0.5V/cm. The influence of bacterial mediated process was evaluated in real contaminated farming soil followed by pilot scale experiment. The in-situ formation of β-cyclodextrin from starch in the treatments had also influence on the significant removal of the pollutants from the farming soil. The conductivity of the soil was effectively reduced from 15.5dS/m to 1.5dS/m which corroborates well with the agricultural norms. The bio-stimulation was confirmed by the increase of the phosphorus content in the treated soil. Finally, phytotoxicity assays demonstrated the viability of the developed technique for soil remediation because plant germination percentage was higher in the treated soil in comparison to untreated soil.

Influence of Long Term Application of Green Manure on the Productivity of Coconut Cultivated in Reddish Brown Latosolic Soils in Sri Lanka

Organic matter contributes in maintaining soil fertility in agriculture. Green leaf biomasses of Gliricidia sepium and Tithonia diversifolia are high in plant nutrients and recognized as potential green manure sources for many crops. In a field experiment carried out in a coconut plantation with Reddish Brown Latosolic soil, two green manure crops were grown to study their abilities and establishment in coconut avenues and to evaluate their effect on nut yield. In situ green manuring, especially with legumes, had the most beneficial effect on soil improvement. The use of green biomass alone has improved soil properties. The biomasses of Gliricidia and Tithonia decomposed rapidly after application to the soil, and incorporated biomass would be an effective source of N, P and K for crops. Results showed that, coconut yields were significantly increased with the incorporation of green biomass of Gliricidia and Tithonia than with commercial inorganic fertilizer application. Mean nut yield for five years in the green manure applied plots was (37-46%) significantly (P &lt; 0.05) higher, compared to that of the inorganic fertilizer applied plots towards the latter part of the experiment. Addition of green manure has significantly (P &lt; 0.05) improved the soil parameters i.e. soil N (by 75%), organic C content (by 86%) and soil microbial activity (by 52%). Soil bulk density has been reduced by 20% which enhances the root growth. The improvement of soil moisture content by 92% is of great importance for coconut in withstanding the frequent dry spells which are on increasing trend with the present climatic change situations. There was no significant effect of green manures on soil pH and P but P content was improved with the use of green biomasses of Gliricidia and Tithonia.

Reducing the loss of agricultural productivity due to compact urban development in municipalities of Switzerland

Globally urban growth destroys fertile soils and endangers food security. Fertile soils are often located in the vicinity of existing urban areas. Thus, preserving high-quality soils can conflict with the objective of developing compact urban patterns. In this study, we assess the trade-off between compact urban patterns and urban patterns that can help reduce the loss of agricultural productivity by maintaining fertile agricultural soils. We assess the trade-offs for selected municipalities in Switzerland using a multi-objective evolutionary algorithm to create a front of non-dominated solutions. These results are used as a benchmark against which we compare simulations of a Business-As-Usual urban expansion in Switzerland to estimate the potential for reducing the loss of agricultural productivity. By analysing the front of non-dominated solutions, we show that there are areas of open land that can be converted into residential land without trading-off compactness against agricultural productivity. We show that there is a large potential for reducing the loss of agricultural productivity when optimizing the configuration of urban development. This potential strongly varies between municipalities and seems to depend primarily on the amount of demand for new urban land within each municipality. The proposed methodology of using multi-objective optimization, followed by a post-optimality analysis and including results from business-as-usual development can be used to support the decision-making processes in urban planning.

Conversion of Biomass Waste into Biochar and the Effect on Mung Bean Crop Production

The dependence on chemical fertilizers in agriculture leads to environmental hazards, destruction of biological communities, and poorer soil quality. Addition of biochar in soil alters overall soil properties, encourages microbiota and increases nutrients’ holding and absorption capacity; hence can be used to improve soil fertility for sustainable agriculture. Cow dung (CD), pine wood (PW), and pine needles (PN) found abundantly in the Himalayan region were selected for preparing biochar. Since phosphate solubilizing fungi have also been cited in the literature to enhance plant growth, the Penicillium sp. K4 strain was added along with biochar. A pot experiment with mung bean plants with eight different treatments was conducted. Generally, all the treatments showed a significant increase in growth and yield compared to plants grown in untreated soil. However, the biochar prepared from pine needles was found to be the best. It was observed that addition of biochar to soil influenced the overall growth of plants positively but the inoculation of Penicillium sp. K4 with biochar improved this effect further. Hence, it can be concluded that the addition of bio‐inoculant in biochar can be a useful practice for enhancing crop productivity.

Variability of Effective Micro-organisms (EM) in bokashi and soil and effects on soil-borne plant pathogens

The microbial inoculant ‘Effective Microorganisms’ (EM) has been used to promote soil fertility and plant growth in agriculture. We tested effects of commercial EM products on suppression of soil-borne diseases, microbial activity and bacterial composition in organically managed sandy soils. EM was supplied as microbial stock suspension and fermented organic matter (EM-bokashi). Bioassays for soil-borne disease incidence were conducted with a naturally infested soil and inoculated disease-free organically managed nonamended soils or the same soils amended with EM-bokashi or sterilized EM-bokashi. Soil respiration analysis and denaturing gradient gel electrophoresis (DGGE) were performed to determine microbial activity, and bacterial composition and diversity. Disease incidence of cucumber plants was not affected by EM-bokashi but reduced by sterilized bokashi compared to the control in naturally infested soil. Pythium ultimum damping-off of cucumber in inoculated soil was enhanced by EM-bokashi and sterilized bokashi compared to the control. In one of three soils, infection of carrot by Rhizoctonia solani was reduced by EM-bokashi compared with sterilized bokashi. Soil respiration increased one week after soil amendment with EM-bokashi and sterilized EM-bokashi compared to the control, but not seven weeks later. DGGE showed that two batches of EM products had different microbial communities and soil amendment with EM-bokashi or sterilized EM-bokashi did not change the bacterial community and diversity in two soils. The added microorganisms in EM were possibly outcompeted and did not affect the existing bacterial community. We conclude that EM did not consistently suppress soil-borne diseases or change microbial activity and bacterial composition and diversity.

Time-dependent shifts in populations and activity of bacterial and archaeal ammonia oxidizers in response to liming in acidic soils

During the past decades, extensive nitrogen fertilization and acid deposition have greatly contributed to soil acidification in agroecosystems. Liming, the addition of calcium- and magnesium-rich material to soil, is an effective management strategy used to improve fertility and productivity of agricultural soils degraded by acidification. Nitrification plays a central role in nitrogen (N) availability in agroecosystems and contributes to soil acidification. However, little is known regarding the effects of liming on this process and microbial populations that drive it. Here, we investigated population dynamics and activity of ammonia oxidizers in response to a 2-year liming field trial in acidic soils received long-term fertilization with chemical N fertilizers and short-term lime amendment in microcosm incubations. Our results showed that activity, abundance and population structure of both ammonia-oxidizing archaea (AOA) and bacteria (AOB) were sensitive to liming in fertilized acidic soils. AOB abundance and potential nitrification rates increased in field plots subjected to liming, whereas the opposite was observed for AOA. In microcosm incubations, AOA abundance increased progressively over 60 days, namely under low CaO levels, whereas AOB abundance was greatly stimulated only during the first week under high CaO levels. 13CO2-SIP-DNA experiments further supported that AOA were the most active ammonia oxidizers in fertilized field soils. However, in N-fertilized soils freshly amended with CaO, only autotrophic growth of AOB was observed after seven days, but not after 30 days when growth of AOA was observed. Taken together, our results indicated that both AOA and AOB play a role in nitrification following liming in fertilized acidic soils, likely through selection of better adapted clades of organisms. Although AOA were likely the main drivers of nitrification in these soils in the long-term, liming stimulated AOB activity in the short-term.

Mecanismos de acción de hongos y bacterias empleados como biofertilizantes en suelos agrícolas: una revisión sistemática

&lt;p&gt;El fósforo, el nitrógeno, el hierro y el potasio son&lt;br /&gt;algunos compuestos necesarios para el crecimiento&lt;br /&gt;y desarrollo vegetal. Los fertilizantes químicos&lt;br /&gt;empleados para aumentar su concentración afectan&lt;br /&gt;significativamente el medioambiente y los ecosistemas&lt;br /&gt;del suelo. De acuerdo con la literatura científica, los&lt;br /&gt;microorganismos con potencial biofertilizante han&lt;br /&gt;demostrado poseer diversos mecanismos de acción&lt;br /&gt;para solubilizar estos compuestos y así cumplir con&lt;br /&gt;los requerimientos de las plantas. La presente revisión&lt;br /&gt;sistemática recopila información científica (publicada&lt;br /&gt;entre los años 2004 y 2014) que describe los&lt;br /&gt;mecanismos de acción de los biofertilizantes microbianos&lt;br /&gt;en suelos agrícolas. Se usaron tres bases de&lt;br /&gt;datos: ScienceDirect, SpringerLink y Scopus,&lt;br /&gt;mediante la ruta de búsqueda (biofertilizer) AND&lt;br /&gt;(bacteria OR fungi) AND (effect OR action OR mechanism).&lt;br /&gt;Tras la comprobación con diversos criterios de&lt;br /&gt;inclusión y exclusión, la búsqueda arrojó un total de&lt;br /&gt;63 artículos originales, incluyendo seis de publicaciones&lt;br /&gt;no indexadas. Como resultado de la revisión&lt;br /&gt;sistemática, se evidenció que la producción de&lt;br /&gt;diversos ácidos orgánicos permite la acidificación&lt;br /&gt;del suelo, lo cual facilita la absorción de los elementos.&lt;br /&gt;También se pudo observar que la solubilización de&lt;br /&gt;fósforo es el mecanismo más frecuentemente descrito,&lt;br /&gt;obtenido por Pseudomonas pseudoalcaligenes con&lt;br /&gt;hasta 726,5 mg/L de solubilización en este elemento.&lt;/p&gt;

Physicochemical, Geochemical and Mineralogical Aspects of Agricultural Soils in Limpopo Province, South Africa

ABSTRACTSoil samples were collected from three selected sites (uncultivated, cultivated and grazing land) at University of Limpopo Experimental Farm (Syferkuil) in Mankweng area to characterise their physicochemical, geochemical and mineralogical properties and their influence on soil fertility for agriculture. Soil textural triangle using Texture Auto Lookup Software (TAL 4.2) Package was used to determine particle sizes of samples which were all dominated by a loamy texture. Chemical characterisation carried out included determination of exchangeable cations, major elemental oxides and trace elements. Silica was the dominant oxide with the highest weight percentage values ranging from 75.99 to 83.45. Chemical index of alteration values of 66 to 75 depicted moderate silica weathering with depletion of soil nutrients due to leaching. Seven minerals were identified i n soil samples which were dominated by kaolinite. The presence of mica and smectites in the soils displayed properties typical of soils rich ...