Effects of winter buds on winter nitrogen uptake and allocation in Pinus densiflora saplings

Studies of nitrogen (N) use by plants have confirmed some winter N uptake; however, the mode of regulation of plant N use in winter is unknown. The regulation of N use by plants during winter may differ from that in the growing season, as plant growth strongly affects N use. We investigated the effects of winter buds on winter N use by Japanese red pine (Pinus densiflora), as a previous study demonstrated that N absorbed during winter contributes significantly to leaf growth in the following spring. We conducted a bud pruning experiment during winter to examine the effects of winter buds on winter N uptake and allocation among plant organs using ¹⁵N labeling. Over a three-week labeling period, the ¹⁵N content in roots increased to 0.20 ± 0.12 mg N g DW^?1, which is equivalent to 1.8 ± 1.1 % of the total N content in the roots. However, this absorbed ¹⁵N rarely appeared in needles and buds. Bud pruning did not affect ¹⁵N uptake and allocation. On the other hand, significant total N retranslocation was found within the crowns of saplings without bud pruning, but N was not retranslocated in bud-pruned plants. The bud pruning experiment indicated that N was retranslocated from needles into winter buds. Since soil N availability changes dramatically and is unstable in many forest ecosystems, N contained in needles would be a more stable source of N than newly absorbed N.     

Impacts of low-intensity prescribed fire on microbial and chemical soil properties in a <Emphasis Type="Italic">Quercus frainetto</Emphasis> forest

Prescribed fire is a common economical and effective forestry practice, and therefore it is important to understand the effects of fire on soil properties for better soil management. We investigated the impacts of low-intensity prescribed fire on the microbial and chemical properties of the top soil in a Hungarian oak (Quercus frainetto Ten.) forest. The research focused on microbial soil parameters (microbial soil respiration (R_SM), soil microbial biomass carbon (Cmic) and metabolic quotient (qCO₂) and chemical topsoil properties (soil acidity (pH), electrical conductivity (EC), carbon (C), nitrogen (N), C/N ratio and exchangeable cations). Mean annual comparisons show significant differences in four parameters (C/N ratio, soil pH, Cmic and qCO₂) while monthly comparisons do not reveal any significant differences. Soil pH increased slightly in the burned plots and had a significantly positive correlation with exchangeable cations Mg, Ca, Mn and K. The mean annual C/N ratio was significantly higher in the burned plots (28.5:1) than in the control plots (27.0:1). The mean annual Cmic (0.6 mg g^?1) was significantly lower although qCO₂ (2.5 µg CO₂–C mg Cmic h^?1) was significantly higher, likely resulting from the microbial response to fire-induced environmental stress. Low-intensity prescribed fire caused very short-lived changes. The annual mean values of C/N ratio, pH, Cmic and qCO₂ showed significant differences.     

Effects of <Emphasis Type="Italic">Faidherbia albida</Emphasis> canopy and leaf litter on soil microbial communities and nitrogen mineralization in selected Zambian soils

The nitrogen status of most Zambian soils is inherently low. Nitrogen-fixing trees such as Faidherbia albida (F. albida) could have the potential to restore soil fertility. We conducted a study to examine the role of mature F. albida trees on the soil microbial communities and overall N fertility status in Zambia. Soil samples were collected under and outside the canopies of F. albida trees in representative fields from two sites namely; Chongwe (loamy sand) and Monze (sandy loam). To assess the long term canopy effects; total N, mineral N and soil organic carbon (C_org) content were directly measured from soils collected under and outside the canopy. Short term litter effects were assessed by subtracting concentrations of biochemical properties of non-amended controls from amended soils with F. albida litter during an 8 week incubation experiment. We also determined N mineralization rates, microbial community structure—Phospholipid fatty acids, microbial biomass carbon, and labile organic carbon (\({\text{C}}_{{{\text{org[K}}_{ 2} {\text{SO}}_{ 4} ]}}\)) during incubation. For the long term canopy effect, average N mineralization rate, C_org, total N and mineral N content of non-amended soils under the canopy were (all significant at p < 0.05) greater than soils outside the canopy on both sites. In the short term, amending soils with litter significantly increased N mineralization rates by an average of 0.52 mg N kg^?1 soil day^?1 on soil from Monze. Microbial biomass carbon measured after 4 weeks of incubation was on average significantly higher on amended soils by 193 and 334 mg C kg^?1 soil compared with non-amended soils in Chongwe and Monze soils, respectively. After 6 weeks of incubation, the concentration of all selected biomarkers for major microbial groups concentrations in non-amended soils were significantly higher (all p < 0.05) under the canopy than outside in Monze soil. Using principal component analysis, we found that the segregation of the samples under and outside the canopy by the first principal component (PC1) could be attributed to a proportional increase in abundances of all microbial groups. Uniform loadings on PC1 indicated that no single microbial group dominated the microbial community. The second principal component separated samples based on incubation time and location. It was mainly loaded with G-positive bacteria, and partly with G-negative bacteria, indicating that microbial composition was dominated by these bacterial groups probably at the beginning of the incubation on Monze soils. Our results show that the improvement of soil fertility status by F. albida could be attributed to a combination of both long term modifications of the soil biological and chemical properties under the canopy as well as short term litter fall addition.     

Greenhouse biofumigation with <Emphasis Type="Italic">Melia azedarach</Emphasis> controls <Emphasis Type="Italic">Meloidogyne</Emphasis> spp. and enhances soil biological activity

The need for environmentally friendly agricultural practices has led to the development of plant-based nematicides for root-knot nematode control. The efficacy of these botanicals has been tested primarily under laboratory and rarely under actual field conditions. Moreover, any side effects on non-target soil organisms that support soil biological activity are usually ignored. Herein, we evaluate the efficacy of Melia azedarach preparations against Meloidogyne spp. in a tomato greenhouse, by root gall examination and soil J2 enumeration. We also assessed side effects on soil microbes through PLFA analysis and microbivorous nematodes, and we quantified several plant growth parameters (e.g., fruit number and weight, root weight). Different treatments within the greenhouse included M. azedarach ripe fruit powder (MFP), ripe fruit water extract (MWE) and furfural, one of the principal active ingredients of M. azedarach and previously known to exhibit fumigant nematicidal activity. Results were compared to those obtained with the commercial nematicide oxamyl (Vydate^® 10 SL) and an untreated control. All treatments were repeated every 20 days throughout the cultivation period. MFP and MWE suppressed Meloidogyne spp. often at the same levels obtained by furfural and oxamyl treatments and enhanced soil biological activity, as indicated by the proliferation of soil microbes and microbial feeding nematodes. Furfural and oxamyl adversely affected the soil community, especially the free-living nematodes. Moreover, furfural was phytotoxic to tomato plants in spite of its natural origin.     

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m^?2/16.06 mg m^?2) and autumn (9.7 m^?2/16.98 mg m^?2) and minimum in the summer (0.43 m^?2/1.26 mg m^?2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO₂–C g soil^?1 day^?1) and minimum in winter (0.24 mg CO₂–C g soil^?1 day^?1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.     

Short-term changes in the soil carbon stocks of young oil palm-based agroforestry systems in the eastern Amazon

The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha^?1) and high (87.6 ± 3.3 Mg C ha^?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha^?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha^?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha^?1 and between oil palm: 10.6 ± 0.5 Mg C ha^?1) and the strip area (17.0 ± 1.4 Mg C ha^?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha^?1 year^?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding.     

Phosphorus dynamics and solubilizing microorganisms in acid soils under different land uses of Lesser Himalayas of India

Although chemical and some soil physical properties have been studied under different land uses of the Lesser Himalayas of India, very limited information is available on soil biochemical properties. Hence we investigated phosphorus (P) fractions [total P (TP), inorganic P (P_i), organic P (P_o), available P, microbial biomass P (MBP)], enzyme activities [dehydrogenase, phosphatases, phytase], phosphate solubilizing bacteria (PSB) and fungi (PSF), and their correlations of acid soils (0–15 and 15–30 cm depths) under different land uses (viz, organic farming, maize–wheat, apple orchard, undisturbed oak forest and uncultivated land of the Indian Himalayas). All land use systems differed significantly for the P fractions, except TP. The highest values for TP, P_i, available P and MBP were found in soils under oak forest and lowest in uncultivated land. However, P_o content was highest in apple orchard. The organic farming (organic manures field under garden pea-french bean cropping system for > 10 years) maintained highest activities of dehydrogenase, acid phosphatase and alkaline phosphatase. The highest phytase activity and highest numbers of PSB (99 × 10³ g^?1 soil) and PSF (30 × 10³ g^?1 soil) were observed in the rhizosphere soils of oak forest. Significant relationships between soil P fractions and enzyme activities, except alkaline phosphatase, were recorded in surface soil layer. PSB and PSF population were also correlated significantly with P fractions and enzyme activities. This would lead us to understand the level of degradation of P pools due to cultivation over forest system and the suitable management practices needed for soil quality restoration.     

Soil properties and microbial functional structure in the rhizosphere of Pinus densiflora (S. and Z.) exposed to elevated atmospheric temperature and carbon dioxide

Rhizosphere-induced changes of Pinus densiflora (S. and Z.) grown at elevated atmospheric temperature and carbon dioxide are presented based on experiments carried out in a two-compartment rhizobag system filled with forest soil in an environmentally controlled walk-in chamber with four treatment combinations: control (25°C, 500 μmol mol^?1 CO₂), T2 (30°C, 500 μmol mol^?1 CO₂), T3 (25°C, 800 μmol mol^?1 CO₂), and T4 (30°C, 800 μmol mol^?1 CO₂). Elevated temperature and atmospheric carbon dioxide resulted in higher concentration of sugars and dissolved organic carbon in soil solution, especially at the later period of plant growth. Soil solution pH from the rhizosphere became less acidic than the bulk soil regardless of treatment, while the electrical conductivity of soil solution from the rhizosphere was increased by elevated carbon dioxide treatment. Biolog EcoPlate? data showed that the rhizosphere had higher average well color development, Shannon–Weaver index, and richness of carbon utilization compared with bulk soil, indicating that microbial activity in the rhizosphere was higher and more diverse than in bulk soil. Subsequent principal component analysis indicated separation of soil microbial community functional structures in the rhizosphere by treatment. The principal components extracted were correlated to plant-induced changes of substrate quality and quantity in the rhizosphere as plants’ response to varying temperature and atmospheric carbon dioxide.     

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a <Emphasis Type="Italic">Larix gmelinii</Emphasis> plantation in China

Continuous increases in anthropogenic nitrogen (N) deposition are likely to change soil microbial properties, and ultimately to affect soil carbon (C) storage. Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch (Larix gmelinii) plantation. In a 9-year experiment in the plantation, N was applied at 100 kg N ha^?1 a^?1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However, soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However, microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, δ¹³C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition (1) altered microbial biomass and activity without affecting soil C in light fractions and (2) resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.     

Analysis of growth and nutrition of a young Castanea �� coudercii plantation after application of wood-bark ash

The aim of the present study was to evaluate the effects of the application of wood-bark ash (WBA) on the growth and nutritional status of a 5-year-old hybrid chestnut plantation in two consecutive periods of 3 and 4 years, i.e., from age 5 to 8 years and from age 8 to 12 years, respectively. A field experiment, which included 3 treatments and 4 replicate blocks, was established on an acidic, organic matter-rich mineral soil. The treatments were two different doses of ash (10 and 20 t ha^?1) and an unfertilized control. Application of the ash (by spreading on the ground) produced mean increases of 16% in diameter and 11% in height growth of trees during the first 3 years, considering both doses together; the response was also significant for the subsequent period, particularly with the higher dose of ash (increases of 11% in diameter and 15% in height growth). The ash had a marked effect, although clearly short lived, on pH (H₂O) levels (an increase of 0.6 units) and on exchangeable soil K, Ca and Mg. The nutritional status of the plantation was improved, mainly in terms of K, Ca and Mg, and the results of a vector analysis indicated that these elements, particularly K, were limiting forest production. Foliar or soil nutrient concentrations in the mineral soil were no longer affected by the ash at age 12 years. We recommend the application of two doses of 10 Mg ha^?1 throughout the rotation for fertilizing acid mineral soils that are rich in organic matter.     

Forest-type shift and subsequent intensive management affected soil organic carbon and microbial community in southeastern China

In this study, we investigated the effect of forest types changes (from coniferous and broadleaf mixed forest (CBMF) to plantation forests of bamboo (Phyllostachys pubescens forest, MBF) and hickory (Carya cathayensis forest, CHF)) combined with intensive management on soil organic carbon (SOC) and microbial community structure, using the ¹³C-nuclear magnetic resonance (NMR) and phospholipid fatty acid (PLFA). The results indicated that soil organic carbon significantly decreased by 30.7 and 28.5% in MBF and CHF, respectively. The aromatic C and aromaticity also significantly decreased in MBF and CHF (P < 0.05), while alkyl, O-alkyl and carbonyl C contents increased (P > 0.05). Significant changes of the soil microbial community were found after the forest type changed from CBMF to MBF and CHF. Total soil microbial PLFAs, soil bacteria PLFAs, fungus PLFAs, actinobacteria PLFAs, arbuscular mycorrhizal fungi PLFAs and protozoan PLFAs ranked as follows: CBMF > CHF > MBF (P < 0.05). The ratio of soil fungus to bacteria was in the order of MBF (0.78) > CHF (0.66) > CBMF (0.49) (P < 0.05), while an opposite order was found for ratio of G+/G− values (CBMF > CHF > MBF, P < 0.05). The converting CBMF into MBF and CHF combined with fertilization and tillage significantly changed the SOC and microbial community. Therefore, necessary measures should be taken to improve the SOC and soil fertility in the MBF and CHF.

     

Evaluating changes in switchgrass physiology,biomass, and light-use efficiency under artificial shade to estimate yields if intercropped with Pinus taeda L.

There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel intercrop in forestry systems. However, there are limited data on the longevity of intercropped bioenergy crops, particularly with respect to light availability as the overstory tree canopy matures. Therefore, we conducted a greenhouse study to determine the effects of shading on switchgrass growth. Four treatments, each with different photosynthetically active radiation (PAR) levels, were investigated inside the greenhouse: control (no shade cloth, 49 % of full sunlight), low (under 36 % shade cloth), medium (under 52 % shade cloth), and heavy shade (under 78 % shade cloth). We determined the effect of shading from March to October 2011 on individually potted, multi-tillered switchgrass transplants cut to a stubble height of 10 cm. In the greenhouse, there was a reduction in tiller number, tiller height, gas exchange rates (photosynthesis and stomatal conductance), leaf area, above- and belowground biomass and light-use efficiency with increasing shade. Total (above- and belowground) biomass in the control measured 374 ± 22 compared to 9 ± 2 g pot^?1 under heavy shade (11 % of full sunlight). Corresponding light-use efficiencies were 3.7 ± 0.2 and 1.4 ± 0.2 g MJ^?1, respectively. We also compared PAR levels and associated aboveground switchgrass biomass from inside the greenhouse to PAR levels in the inter-row regions of a range of loblolly pine (Pinus taeda L.) stands from across the southeastern United States (U.S.) to estimate when light may limit the growth of intercropped species under field conditions. Results from the light environment of loblolly pine plantations in the field suggest that switchgrass biomass will be significantly reduced at a loblolly pine leaf area index between 1.95 and 2.25, which occurs on average between ages 6 and 8 years across the U.S. Southeast in intensively managed pine plantations. These leaf area indices correspond to a 60–65 % reduction in PAR from open sky.     

Effects of pruning and stand density on the productionof new epicormic shoots in young stands of pedunculate oak (Quercus robur L.)

Context

Avoidance or control of epicormic shoots is among the major silvicultural challenges for the production of high-quality oak timber. In northern Europe, contemporary oak silviculture aims to produce valuable timber on a relatively short rotation, applying early, heavy thinning combined with artificial pruning.

Aims

The aim of this study was to analyse the effects of pruning and stand density on the production of new epicormic shoots on young trees of pedunculate oak (Quercus robur L.).

Methods

The study was based on two field experiments in even-aged stands of pedunculate oak subjected to different thinning practices and early selection of potential future crop trees. From ages 13 to 15 years, stem density was reduced to 300 trees ha^?1, 1,000 ha^?1 or stands remained unthinned. Pruning was conducted on selected trees at ages 22–24 years. At that age, the stem density in unthinned control plots ranged from 2,500 to 3,100 ha^?1. All treatments were replicated twice within each experiment.

Results

Pruning led to an overall increase in the total production of new epicormic shoots. More epicormic shoots were produced in the lower part of the stem (0–3 m in height) than in the upper part (3–6 m). The number of new epicormic shoots increased with increasing stand density.

Conclusion

Early, heavy thinning combined with high pruning at regular intervals may help shorten the rotation length for pedunculate oak without further reduction in wood quality than that which is caused by wider annual growth rings.     

Precipitation influences on active fractions of soil organic matter in seasonally dry tropical forests of the Yucatan: regional and seasonal patterns

In a transect study involving 15 mature seasonally dry tropical forests growing on uniform geological substrate in the Yucatan Peninsula, Mexico, we analyzed the influence of a large reduction in mean annual precipitation (1,036–537 mm year^?1) on carbon (C) and nitrogen (N) pools in soils. We investigated the C content in organic soil and in active fraction pools (organic matter and microbial biomass) and analyzed the dependence of these pools on precipitation. Carbon (total, inorganic and organic, and in microbial biomass) and N (total) concentrations in bulk soil decreased as rainfall increased from <600 mm year^?1 >1,000 mm year^?1. Additionally, in all organic matter fractions, C and N concentrations generally decreased with greater precipitation. Soil average C mineralization decreased by 61 % from the wettest to the driest region. Reduced precipitation during the dry season increased microbial biomass C and water-extractable C concentrations and decreased the C concentration in organic matter fractions. No other significant changes were observed between seasons in C concentrations, N concentrations or C mineralization. Overall, we conclude that physical (macroclimate) and biological processes are more active in soils in the wettest region, resulting in a faster turnover of organic matter.     

Variation of soil enzyme activity and microbial biomass in poplar plantations of different genotypes and stem spacings

To improve the productivity of poplar plantations, a field experiment of split-plot design with four tree spacings and three poplar clones was established, and four soil enzyme activities and microbial biomass were monitored in the trial.Soil enzyme activities, in most cases,were significantly higher in topsoil(0–10 cm) than in lower horizons(10–20 cm).Soil cellulase, catalase and protease activities during the growing season were higher than during the non-growing season, while invertase activity followed the opposite trend.Soil invertase, cellulase and catalase activities varied by poplar clone but soil protease activity did not.Cellulase and protease activities in the plantation at 5×5 m spacing were significantly higher than in the other spacings.The highest catalase activity was recorded at 6×6 m spacing.At the same planting density, invertase activity was greater in square spacings than in rectangular spacings.Soil microbial biomass was also significantly affected by seedling spacing and poplar clone.The mean soil MBC was significantly lower in topsoil than in the lower horizon, while MBN showed the opposite pattern.Significantly positive correlations were observed among soil cellulase, protease and catalase activities(p0.01), whereas soil invertase activity was negatively and significantly correlated with cellulase, protease and catalase activities(p0.01).Soil microbial biomass and enzyme activities were not correlated except for a significantly negative correlation between soil MBC and catalase activities.Variations in soil enzyme activity and microbial biomass in different poplar plantations suggest that genotype and planting spacing should be considered when modeling soil nutrient dynamics and managing for long-term site productivity.     

Interactive effects of irrigation and exponential fertilization on nutritional characteristics in <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">euramericana</Emphasis> cv. ‘74/76’ cuttings in an open-air nursery in Beijing,China

Nutritional characteristics determine tree stock quality to a considerable extent. Exponential fertilization can induce nutrient reserves within juvenile trees, but its validity on poplar is contingent on interaction with a scientific irrigation regime due to limited water resources under global warming. In the present study, we raised 3200 Populus × euramericana cv. ‘74/76’ cuttings under four irrigation regimes of 0 (I0), 60 % (I60), 80 % (I80), and 100 % (I100) of field capacity for soil moisture content with or without (control) the employment of nitrogen (N) addition delivered as exponential fertilization at the rate of 8 g N cutting^?1 (E8) in an open-air nursery in Beijing, China. Both height and diameter increased with the increment of soil moisture ratio or in response to exponential fertilization (EF) without any interactive effects. In general, concentrations of N, phosphorus (P), and potassium (K) declined with time in stem but foliar N concentration did not change. Under the I100 regime, EF increased foliar N concentration relative to the control but failed to affect N concentration in stem in September, when both N concentration and N content were increased by EF under the I80 regime. Stem-K content and concentration by EF under the I80 regime also increased in September, therefore EF-treated cuttings had a higher ratio of K content in stem to that in whole plant (%ANAR). Vector diagnosis for nutritional status indicated that EF resulted in dilution of K concentration but induced a steady-state P uptake in leaves under all irrigation regimes. Therefore, EF of N addition could promote N uptake to leaves of P. × euramericana cv. ‘74/76’ cuttings, but it had a null effect on N and P reserves in stem and impaired K reserves. In conclusion, the irrigation regime of 80 % field capacity of soil moisture content was suggested for the culture of juvenile P. × euramericana cv. ‘74/76’ cuttings. As the interactive meaning, EF was also suggested for its excellent promotion on both N and K uptakes.     

Impact of drip fertigation on arecanut–cocoa system in humid tropics of India

A 5-year field trial was conducted on a laterite soil to evaluate the effects of organic and inorganic fertigations in arecanut sole and arecanut–cocoa land use systems at Vittal, India. Arecanut registered similar yield levels in sole and arecanut–cocoa cropping situations (3,022–3,117 kg ha^?1). Fertigation of 75 % NPK, vermicompost extract (VCE) 20 % N and VCE (10 and 20 % N)+25 % NPK registered the same yield levels (3,029–3,375 kg ha^?1). Dry bean yield of cocoa was at par with fertigation of 75 % NPK and 20 % N VCE + 25 % NPK (291–335 kg ha^?1). Fertigation @ 75 % NPK increased the yield of cocoa by 52 % over VCE alone. The productivity per unit area (kg ha^?1) was significant and higher by 12 % in arecanut–cocoa system (3,450) than arecanut sole (3,090). Productivity was similar to fertigation of 75 % NPK, 20 % N VCE and VCE (10 or 20 % N) + 25 % NPK (3,316–3,665 kg ha^?1). Leaf nutrient status of arecanut and cocoa indicated lower levels of N and K and above normal levels of Ca, Mg and micronutrients. The results indicate that drip fertigation increases the productivity, but precision application of N and K is required for sustaining the yields.     

Effect of multipurpose tree species on soil fertility and CO2 efflux under hilly ecosystems of Northeast India

A 26 years old agroforestry plantation consisting of four multipurpose tree species (MPTs) (Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex-Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were compared with a control plot (without tree plantation) for soil fertility status and CO₂ efflux. The presence of trees improved all the physico-chemical and microbial biomass parameters studied in this experiment. Relative to control, soils under MPTs showed significant increases of 17 % soil organic carbon, 26 % available nitrogen (AN), 28 % phosphorus (AP), 50 % potassium (AK), 65 % mean weight diameter (MWD) of aggregates, 21 % moisture and 34 % soil microbial biomass carbon (MBC) while reducing the mean bulk density (7 %). However, these parameters significantly differed among the tree species i.e., soils under A. nepalensis and M. oblonga had higher values of these attributes except bulk density, than under other species. Irrespective of treatments, the values of all these attributes were higher in surface soils while bulk density was highest in subsurface (60–75 cm). Cumulative CO₂ efflux under MPTs was significantly higher (15 %) and ranged from 1.71 g 100 g^?1 (M. oblonga) to 2.01 g 100 g^?1 (A. nepalensis) compared to control at 150 days of incubation. In all the treatments, increment in temperature increased the oxidation of soil organic matter, thereby increased the cumulative CO₂ efflux from soils. Of the tree species, with increment in temperature, A. nepalensis recorded more CO₂ efflux (2.50 g 100 g^?1) than other MPTs but the per cent increase was more in control plot. P. kesiya and A. nepalensis recorded highest activation energy (59.1 and 39 kJ mol^?1, respectively). Net organic carbon sequestered in soil was highest under A. nepalensis (25.7 g kg^?1) followed by M. oblonga (19.3 g kg^?1), whereas control showed the lowest values. Amount of net carbon stored in the soil had significant and positive correlation with MBC (r = 0.706**), MWD (r = 0.636*), and AN (r = 0.825**).     

Responses of labile soil organic carbon and enzyme activity in mineral soils to forest conversion in the subtropics

Aims

Globally, extensive areas of native forest have been almost replaced by plantations to meet the demands for timber, fuel material and other forest products. This study aimed to evaluate the effects of forest conversion on labile soil organic C (SOC), soil respiration, and enzyme activity, and to quantify their relationship in subtropical forest ecosystems.

Methods

Surface mineral soil (0–20 cm) was collected from a Cunninghamia lanceolata Hook. plantation, Pinus massoniana Lamb. plantation, Michelia macclurei Dandy plantation, and an undisturbed native broadleaf forest. Soil microbial biomass C, dissolved organic C, permanganate-oxidizable C, basal respiration, and six enzyme activities were investigated.

Results

Soil microbial biomass C was higher by 45.9 % in native broadleaf forest than that in M. macclurei Dandy plantation. The ratio of soil microbial biomass C to total SOC was 27.6 % higher in the M. macclurei Dandy plantation than in the native broadleaf forest. The soil respiration increased by 25.2 % and 21.7 % after conversion from native broadleaf forest to P. massoniana Lamb. and M. macclurei Dandy plantations respectively. The effects of forest conversion on the soil enzyme activities differed among the tree species. Soil microbial biomass C had higher correlation with soil respiration than with the other SOC fractions. Moreover, soil microbial biomass C was positively correlated with urease and negatively correlated with cellulase activity. Soil respiration had higher correlation with soil microbial biomass C, dissolved organic C and permanganate-oxidizable C.

Conclusion

Forest conversion affected the soil microbial biomass C, soil respiration, invertase, cellulase, urease, catalase, acid phosphatase, and polyphenol oxidase activities, but their response depended on tree species. Soil respiration was mainly controlled by labile SOC, not by total SOC.     

Effects of parent material on soil microbial biomass carbon and basal respiration within young afforested areas

Afforestation is economically and ecologically important for protecting land and improving soil quality. This study evaluates how soil basal respiration, physicochemical and microbiological characteristics are affected by parent material variety in afforesting degraded areas. For this, some soil physical and chemical parameters, microbial respiration (MR), soil microbial biomass carbon and microbial indexes (C_mic/C_org and MR/C_mic) were determined. The results showed that the physical, chemical and microbiological properties of the soil formed from limestone were better than those of the basaltic-andesite soil. An independent samples t-test demonstrated that the afforested area on the limestone parent material had significantly higher microbial biomass C than the basaltic-andesite parent material. The microbial quotient (C_mic/C_org) of the limestone soil was positively affected by afforestation. In addition, the highest basal respiration value (1.01?±?0.33 CO₂–C 10^?2?µg?g^?1?h^?1) was observed for the limestone at the topsoil. The lowest metabolic quotient values were determined for the basaltic-andesite parent material on both topsoil and subsoil (1.99 and 1.42?μg CO₂-C mg C_mic^?1 h^?1, respectively). This study revealed the importance of determining the parent material and its soil characteristics for successfully managing forest applications in degraded areas. Limestone soil sequesters more carbon and promotes microbial activities with a higher C_mic/C_org than the basaltic-andesite soil. Furthermore, the microbial quotient remained low during the 10 years in which the forest was in its sapling stage.