The present study was conducted to see the short term impact of organic and inorganic fertilizers on soil microbial biomass both in spring and summer. Also aimed to observe the correlation between soil microbial biomass and soil DNA. The study concluded that type of fertilizer might alter the soil microbial biomass and DNA contents. In soil treated with organic fertilizers resulted in higher concentrations of microbial biomass and DNA contents in summer as compared to spring dute to increase in temperature. Correspondingly, in case of inorganic fertilizer, concentrations of soil microbial biomass and DNA detected higher in summer instead of spring. The statistical correlation between soil microbial biomass, DNA and ODR in spring and summer along with organic and inorganic fertilizers were calculated highly significant (p>0.01). This study demonstrated the impact of fertilizers and seasonal variations on soil microbial biomass and also revealed significant correlation between soil microbial biomass and soil DNA.

International audience | Preservation and sustainable use of soil biological communities represent major challenges in the current agroecological context. However, to identify the agricultural practices/systems that match with these challenges, innovative tools have to be developed to establish a diagnosis of the biological status of the soil. Here, we have developed a statistical polynomial model to predict the molecular biomass of the soil microbial community according to the soil physicochemical properties. For this, we used a dataset of soil molecular microbial biomass estimates and pedoclimatic properties derived from analyses of samples collected in the context of the “French monitoring soil quality network = Réseau de Mesures de la qualité des Sols” (RMQS). This sampling network has provided 2115 soil samples covering the range of variability of soil type and land use at the scale of France. The best model obtained from the data showed that soil organic carbon content, clay content, altitude, and pH were the best explanatory variables of soil microbial biomass while other variables such as longitude, latitude and annual temperature were negligeable. Based on these variables, the multilinear model developed allowed very accurate prediction of the soil microbial biomass, with an excellent adjusted coefficient of determination of 0.6772 (P < 10−3). In addition to , the model was further validated by results from cross validation and sensitivity analyses. The model provides a reference value for microbial biomass for a given pedoclimatic condition, which can then be compared with the corresponding measured data to provide for the first time a robust diagnosis of soil quality. Application of the model to a set of soil samples obtained at the scale of an agricultural landscape is presented and discussed, showing the suitability of the model to diagnose of the impact of particular agricultural practices such as tillage and catch crops in field conditions, at least over the French nation.

International audience | Preservation and sustainable use of soil biological communities represent major challenges in the current agroecological context. However, to identify the agricultural practices/systems that match with these challenges, innovative tools have to be developed to establish a diagnosis of the biological status of the soil. Here, we have developed a statistical polynomial model to predict the molecular biomass of the soil microbial community according to the soil physicochemical properties. For this, we used a dataset of soil molecular microbial biomass estimates and pedoclimatic properties derived from analyses of samples collected in the context of the “French monitoring soil quality network = Réseau de Mesures de la qualité des Sols” (RMQS). This sampling network has provided 2115 soil samples covering the range of variability of soil type and land use at the scale of France. The best model obtained from the data showed that soil organic carbon content, clay content, altitude, and pH were the best explanatory variables of soil microbial biomass while other variables such as longitude, latitude and annual temperature were negligeable. Based on these variables, the multilinear model developed allowed very accurate prediction of the soil microbial biomass, with an excellent adjusted coefficient of determination of 0.6772 (P < 10−3). In addition to , the model was further validated by results from cross validation and sensitivity analyses. The model provides a reference value for microbial biomass for a given pedoclimatic condition, which can then be compared with the corresponding measured data to provide for the first time a robust diagnosis of soil quality. Application of the model to a set of soil samples obtained at the scale of an agricultural landscape is presented and discussed, showing the suitability of the model to diagnose of the impact of particular agricultural practices such as tillage and catch crops in field conditions, at least over the French nation.

The effect of fertilizers and amendments on organic matter dynamics in an acid Alfisol was studied in a long-term field experiment initiated during 1972 at experimental farm of Department of Soil Science, CSK HPKV, Palampur (India). Continuous application of chemical fertilizers either alone or in combination with farmyard manure (FYM) or lime for 42 years significantly influenced water-soluble organic carbon (WS-OC), water-soluble carbohydrate (WS-CHO), soil microbial biomass carbon, soil microbial biomass nitrogen, soil microbial biomass phosphorus, soil microbial biomass sulfur, humic acid (HA), and fulvic acid (FA). Continuous cropping without fertilization resulted in depletion to the order of 17, 21, 24, 23, 22, 26, 12, and 18% in WS-OC, WS-CHO, microbial biomass carbon, microbial biomass nitrogen, microbial biomass phosphorus, microbial biomass sulfur, HA, and FA, respectively. Different fractions of soil organic matter were found to be positively and significantly correlated with grain and straw/stover yield of wheat and maize crops.

Switchgrass (Panicum virgatum L.) is a promising bioenergy crop for temperate regions. Overwintering has been used to improve biomass quality, resulting in a more efficient combustion, partially due to a reduction in minerals concentration. This study examines the effects of soil composition on overwintered switchgrass composition. Samples were collected in the spring from 58 environments in Southern Quebec to determine possible relationships between soil composition and biomass quality. Principal component analysis and stepwise regressions were used to identify relationships between soil and biomass compositions. Soil parameters monitored explained 74% of the variation in biomass silicon (Si) concentration, 45% of the variation in ash, and 32% of the variation in magnesium (Mg). Soil composition had limited effects on the concentration of other elements in switchgrass biomass. Switchgrass biomass quality is influenced by soil composition and appears well suited to biomass combustion when overwintered and harvested in the spring.

Thesis (MScConsEcol)--Stellenbosch University, 2016. | ENGLISH ABSTRACT: Removal of woody invasive alien plants from riparian and terrestrial fynbos ecosystems usually leads to the accumulation of large volumes of plant biomass. The three study species, Acacia mearnsii, Acacia saligna and Eucalyptus camaldulensis are well known for their ability to considerably increase above-ground biomass production. While some biomass may be removed for use as timber, or chipped for export, in cases where there is no alternative use for this biomass, or where site accessibility is an issue, burning of biomass in the form of piles or rows is practiced as a way of destroying biomass in situ. However, this approach has been reported to produce high temperatures, which may lead to altered soil properties and destroyed soil stored seed banks. Burn scars may develop on soil surfaces that were exposed to the burning of slash piles, which may remain unvegetated for extended periods of time. As a consequence, restoration may be patchy, uneven or delayed in post-clearing landscapes. The aim of this study was to evaluate the seasonal and spatial effects of burning of slash piles of Acacia spp. and Eucalyptus spp. biomass on soil physicochemical properties. Four riparian study areas (Hermon and Robertson, both dominated by Eucalyptus camaldulensis prior to clearing, and Wit River and Rawsonville, Acacia mearnsii dominated) and one terrestrial study area (Blaauwberg; Acacia saligna) were selected within the fynbos biome. Burning was conducted in spring 2014 (Hermon and Blaauwberg) and winter 2015 for all other study areas. Acacia mearnsii and A. saligna piles had a volume of between 21.01 and 88.17m3 and E. camaldulensis stacks had a volume of between 93.93 and 116.68 m3. Soil samples were collected from the topsoil layer, 0-10 cm depth, prior to burning, post-fire and three subsequently seasons, from within the burn scars (in the centre, an intermediate position, i.e. between the edge and centre, and the edge), from the soil matrix (about 2 m from the edge), from a recovering reference site and from an invaded reference site. The collected samples were subjected to laboratory analyses for pH, electrical conductivity (EC), total carbon (C) and nitrogen (N), available N, available phosphorus (P), exchangeable cations and hydrophobicity. At all study areas, soil pH (water), EC, available P and exchangeable cations increased significantly immediately after burning and had returned to pre-fire levels within one year of sampling, with the exception of soil pH, which persisted longer. This was with the exception of the Wit River riparian study area, where soil pH increased significantly and had returned to pre-fire within 3-4 months of sampling and soil EC was not affected at all. Total C and N responded differently across study areas, where it remained unchanged at Hermon and decreased significantly at Rawsonville. Available N was not initially affected by fire at any of the study areas, but later showed higher levels within fire scars in Acacia invaded areas. No such difference emerged within fire scars of Eucalyptus camaldulensis invaded areas, suggesting that nitrogen may be more readily available in fire scars of riparian Acacia invaded areas. Hydrophobicity increased only at Rawsonville (Acacia mearnsii) as a result of fire and was not affected by fire in other areas. At the terrestrial site, soil pH, EC and available P increased significantly, but returned to pre-fire levels after a few seasons, with the exception of pH, which remained significantly higher. The results from this study indicate that certain parameters such as soil pH, EC, available P and cations generally increase immediately after fire. In addition, the response of other properties including total C and N, available N and hydrophobicity may be governed by the characteristics of the ecosystem, soil type, burn fuel and seasonal variations. The implications of the study are that using fire as a tool for biomass management in post clearing landscapes may introduce unwanted soil physicochemical alterations, which may impact recovery, especially of native species. | AFRIKAANSE OPSOMMING: Die verwydering van houtagtige indringerplante in rivieroewers en terrestriële gebied in die fynbos-ekosisteem lei gewoonlik tot die opeenhoping van groot volumes plantbiomassa. Hierdie studie fokus op drie hoof indringerplantspesies in die Fynbos ekosisteem, naamlik Acacia mearnsii, Acacia saligna en Eucalyptus camaldulensis. Hierdie spesies is bekend vir hul vermoë om die bogrondse biomassa te verhoog. Verder, waar die verwydering van hierdie indringerplante vir kommersiële doeleindes, soos die verkoop van hout nie moontlik is nie, of in gevalle waar daar geen alternatiewe gebruik vir die oorblywende plant biomassa is nie, en waar daar die toeganglikheid van die ooblywende biomass problematies word, word die verbranding van hope of rye biomassa gebruik as 'n manier om van die biomassa ontslae te raak. Hierdie benadering lei tot ’n toename in temperature, wat kan lei tot die veranderinge in grondeienskappe en die vernietiging van die saadbank. Brandletsels kan ontwikkel op grond oppervlaktes weens die impak van vuur. Die impak van vuur verhinder die regenerasie van plante, en areas met brandletsels kan braak le vir lang tye. Die verlies van saadbank na die vuur impak dien as n moontlike faktor hoekom die plant nie kon groei in die gebrande areas nie. Gevolglik kan regenerasie kolsgewys, ongelyk of vertraagd plaasvind in post-restorasie landskappe. Die doel van hierdie studie was om die seisoenale en ruimtelike gevolge van die brand van Acacia en Eucalyptus biomassa op grondeienskappe te evalueer. Vier rivieroewer areas (Hermon en Robertson, gedomineer deur Eucalyptus camaldulensis voor die verwydering van biomass, en Witrivier en Rawsonville, gedomineer deur Acacia mearnsii) en een terrestriële studiegebied (Blaauwberg, Acacia saligna) is gekies in die fynbos bioom. Die brand in Hermon en Blaauwberg is uitgevoer in durende die lente in 2014, terwyl die brand in ander areas in die winter in 2015 uitgevoer is. Die volume van die biomassahope van Acacia mearnsii en A. saligna was tussen 21,01 en 88.17m3, waar van die volume in E. camaldulensis tussen 93,93 en 116,68 m3 was. Grondmonsters is geneem voor die brand, na die brand en drie seisoene opeenvolgend na die brand. Die monsters bevat grond vanaf die boonste grondlaag (0-10 cm diepte) en die monsters is geneem vanuit die volgende areas: (i) in die middel, (ii) by die intermediêre areas (die areas tussen die rand en die middle), (iii) die rand van die biomassahope, en (iv) die grond matriks (sowat 2 m van die rand). ’n Herstelde verwysings area en ’n indringerverwysings areas is ook in die studie ingesluit. Die versamelde monsters is onderwerp aan laboratorium ontleedings vir pH, elektriese geleiding (EG), totale koolstof (C) en stikstof (N), beskikbare N, beskikbare fosfor (P), uitruilbare katione en hidrofobisiteit. Al die areas het getoon dat vlakke van grond pH (water), EG, beskikbare P en uitruilbare katione beduidend toegeneem het na die brand. Al die chemiese eienskappe het teruggekeer na die vlakke voor die vuur, en wel binne ‘n periode van een jaar, met die uitsondering van grond pH, wat langer hoog gebly het. Dit is in teenstelling met die Wit river studiearea, waar grond pH toegeneem het na die vuur en teruggekeer het na vlakke voor die vuur binne 3-4 maande, sonder om die grond EG te affekteer. Elke studie area het verskillende tendense in terme van die totale C en N getoon, byvoorbeeld, die Hermon area het minimale verandering getoon waar Rawsonville ’n statisties beduidende verskil getoon het. Die beskikbare N was aanvanklik nie geraak deur die brand nie, maar later is daar beduidend hoër vlakke binne die gebrand areas van Acacia gevind. Hierdie bevindinge is nie getoon in areas wat beinvloed was deur die brand van Eucalyptus camaldulensis biomassahope nie. Hierdie resultate beteken dat N na die brand meer beskikbaar was in brandletsels in Acacia ingedringde rivieroewerareas. Slegs die Rawsonville (Acacia mearnsii) area het n toename in hidrofobisities na die brand getoon, ‘n tendens wat nie by deur ander areas getoon is nie. By die terrestriële studiearea het die grond pH, EG en beskikbare P aansienlik toegeneem, en al die faktore het teruggekeer na die vlakke voor die vuur na 'n paar seisoene, met die uitsondering van grond pH wat aansienlik hoër gebly het. Die resultate van hierdie studie dui daarop aan dat sekere parameters soos grond pH, EG, beskikbaar P en katione onmiddelik toeneem na ’n brand. Verder, die reaksie van ander eienskappe, insluitend die totale C en N, beskikbaar N en hidrofobisiteit mag moontlik beheer word deur die invloed van die ekosisteem, grondtipe, brandstof en seisoenale variasies. Die implikasies van hierdie studie is dat die gebruik van vuur om oorblywende plant biomassa te beheer (na die verwydering van indringerplante), mag moontlik ongewenste fisiese en chemiese veranderinginge veroorsaak wat die herstel van inheemse spesies kan beinvloed.

Alpine meadow ecosystem is fragile and highly sensitive to climate change. An understanding of the allocation of above- and below-ground plant biomass and correlations with environmental factors in alpine meadow ecosystem can result in better protection and effective utilization of alpine meadow vegetation. We chose an alpine meadow in the Qinghai-Tibetan Plateau of China as the study area and designed experimental warming plots using a randomized block experimental design. We used single-tube infrared radiators as warming devices, established the warming treatments, and measured plant above- (AGB) and below-ground biomass (BGB) during the growing seasons (May to September) in 2012 and 2013. We determined the allocation of biomass and the relationship between biomass and soil environment under the warming treatment. Biomass indices including above-ground biomass, below-ground biomass and the ratio of root to shoot (R/S), and soil factors including soil moisture and soil temperature at different depths were measured. The results showed that (1) BGB of the alpine meadow had the most significant allometric correlation with its AGB (y=298.7x ⁰.⁴⁴, P<0.001), but the relationship decreased under warming treatment and the determination coefficient of the functional equation was 0.102 which was less than that of 0.188 of the unwarming treatment (control); (2) BGB increased, especially in the deeper soil layers under warming treatment (P>0.05). At 0–10 cm soil depth, the percentages of BGB under warming treatment were smaller than those of the control treatment with the decreases being 8.52% and 8.23% in 2012 and 2013, respectively. However, the BGB increased 2.13% and 2.06% in 2012 and 2013, respectively, at 10–50 cm soil depths; (3) BGB had significant positive correlations with soil moisture at 100 cm depth and with soil temperature at 20–100 cm depths (P<0.05), but the mean correlation coefficient of soil temperature was 0.354, greater than the 0.245 of soil moisture. R/S ratio had a significant negative correlation with soil temperature at 20 cm depth (P<0.05). The warmer soil temperatures in shallow layers increased the biomass allocation to above-ground plant parts, which leading to the increase in AGB; whereas the enhanced thawing of frozen soil in deep layers causing by warming treatment produced more moisture that affected plant biomass allocation.

The effects of the interaction between tree species composition and altitude on soil microbial properties are poorly understood. In this study, soil samples (0–20 cm) were collected in August 2011 from Betula platyphylla and Picea crassifolia forests along two different altitudinal gradients. Soil microbial activity and biomass were measured using Biolog-ECO plates and phospholipid fatty acid analysis. Both of the forest soils were characterized by a significantly lower soil pH (p < .05) and higher soil organic matter (SOM) and nutrient levels (total nitrogen, available nitrogen and phosphorus) at higher altitudes compared with lower altitudes. Soil microbial activity was significantly lower in the birch forests (p < .05), but changed little in the spruce forests with increasing altitude. Soil microbial biomass decreased in the two forest soils across altitude gradients. With each 100-m drop in altitude, the soil microbial biomass exhibited a sharper decline in the spruce forests than in the birch forests. SOM had significant negative effects on soil microbial biomass, but no effects on soil microbial activity. Soil pH was significantly negative correlated with soil microbial biomass and activity. The tree species composition exhibited more negative effects on soil microbial biomass in the spruce forests, while altitude had a greater effect in the birch forests.