Build-up Of Soil Research Articles

The biological controls of soil carbon accumulation following wildfire and harvest in boreal forests: A review.

Boreal forests are frequently subjected to disturbances, including wildfire and clear-cutting. While these disturbances can cause soil carbon (C) losses, the long-term accumulation dynamics of soil C stocks during subsequent stand development is controlled by biological processes related to the balance of net primary production (NPP) and outputs via heterotrophic respiration and leaching, many of which remain poorly understood. We review the biological processes suggested to influence soil C accumulation in boreal forests. Our review indicates that median C accumulation rates following wildfire and clear-cutting are similar (0.15 and 0.20 Mg ha-1 year-1, respectively), however, variation between studies is extremely high. Further, while many individual studies show linear increases in soil C stocks through time after disturbance, there are indications that C stock recovery is fastest early to mid-succession (e.g. 15-80 years) and then slows as forests mature (e.g. >100 years). We indicate that the rapid build-up of soil C in younger stands appears not only driven by higher plant production, but also by a high rate of mycorrhizal hyphal production, and mycorrhizal suppression of saprotrophs. As stands mature, the balance between reductions in plant and mycorrhizal production, increasing plant litter recalcitrance, and ectomycorrhizal decomposers and saprotrophs have been highlighted as key controls on soil C accumulation rates. While some of these controls appear well understood (e.g. temporal patterns in NPP, changes in aboveground litter quality), many others remain research frontiers. Notably, very little data exists describing and comparing successional patterns of root production, mycorrhizal functional traits, mycorrhizal-saprotroph interactions, or C outputs via heterotrophic respiration and dissolved organic C following different disturbances. We argue that these less frequently described controls require attention, as they will be key not only for understanding ecosystem C balances, but also for representing these dynamics more accurately in soil organic C and Earth system models.

Long Term Impact of Fertilization and Intensive Cropping on Maize Yield and Soil Nutrient Availability under Sandy Clay Loam Soil (Inceptisol)

A field experiment was conducted to evaluate the impact of crop productivity and soil nutrient availability under continuous cropping and fertilization. A single nutrient application or omission of nutrient or mineral fertilizer alone can deteriorate the soil nutrient availability and yield in long run. The result revealed that soil pH and EC have not changed substantially even after the repeated application of fertilizers over five decades. The use of balanced fertilizers either alone or integrated with organic manure (FYM) has significantly increased the grain and straw yield of maize. The yield increment of maize was observed 13.9 percent higher than 100% NPK and 18.3 percent higher than without the addition of S (S free). Balanced fertilization can improve the soil nutrients (N, P, K & S) and soil organic carbon instead addition of FYM @ 10 t ha-1 could increase the SOC and soil nutrients in long run in a sustainable manner. Concerning nitrogen, single nutrient (N alone) plots received low available nutrients and yield also it’s deteriorated the soil nutrients over long period. A build-up of available soil P and S was observed due to its continuous addition through fertilizer but soil K has reduced because of intensive cropping and high-yielding cultivars. Hence, for sustainable roduction, application of a recommended dose of mineral fertilization (100% NPK) along with FYM @ 10 t ha-1 may be used to achieve a higher yield, stable nutrient balance and soil quality over decades.

Effects of Organic Fertilizers on the Soil Microorganisms Responsible for N2O Emissions: A Review.

The use of organic fertilizers constitutes a sustainable strategy to recycle nutrients, increase soil carbon (C) stocks and mitigate climate change. Yet, this depends largely on balance between soil C sequestration and the emissions of the potent greenhouse gas nitrous oxide (N2O). Organic fertilizers strongly influence the microbial processes leading to the release of N2O. The magnitude and pattern of N2O emissions are different from the emissions observed from inorganic fertilizers and difficult to predict, which hinders developing best management practices specific to organic fertilizers. Currently, we lack a comprehensive evaluation of the effects of OFs on the function and structure of the N cycling microbial communities. Focusing on animal manures, here we provide an overview of the effects of these organic fertilizers on the community structure and function of nitrifying and denitrifying microorganisms in upland soils. Unprocessed manure with high moisture, high available nitrogen (N) and C content can shift the structure of the microbial community, increasing the abundance and activity of nitrifying and denitrifying microorganisms. Processed manure, such as digestate, compost, vermicompost and biochar, can also stimulate nitrifying and denitrifying microorganisms, although the effects on the soil microbial community structure are different, and N2O emissions are comparatively lower than raw manure. We propose a framework of best management practices to minimize the negative environmental impacts of organic fertilizers and maximize their benefits in improving soil health and sustaining food production systems. Long-term application of composted manure and the buildup of soil C stocks may contribute to N retention as microbial or stabilized organic N in the soil while increasing the abundance of denitrifying microorganisms and thus reduce the emissions of N2O by favoring the completion of denitrification to produce dinitrogen gas. Future research using multi-omics approaches can be used to establish key biochemical pathways and microbial taxa responsible for N2O production under organic fertilization.

Bioavailability of phosphorus in granulated and pyrolyzed broiler manure

Production of organic fertilizers from poultry manure may compromise availability of phosphorus (P) to plants. This study examined the effects of granulation, feather meal addition, and pyrolysis on bioavailability of P in broiler manure in a pot experiment with ryegrass and assessed whether P availability is enhanced by inoculating arbuscular mycorrhizal fungi (AMF) into soil. Granulated broiler manure gave similar plant yield and P uptake to superphosphate. Feather meal addition had a minor negative effect on P availability, whereas pyrolysis lowered the fertilization effect of broiler manure. The yield-based mineral-P equivalences were 120%, 85% and 75% during the first harvest, and 100%, 75% and 45% during one growing season for granulated unamended, granulated amended with feather meal and pyrolyzed broiler manure. Soil inoculation with AMF did not enhance P availability. Granulated poultry manure is suitable as a P fertilizer for annual crops with comparable bioavailability to mineral fertilizer P, whereas pyrolyzed poultry manure is suitable as a slow-release or storage P fertilizer in slightly acidic soils. Knowledge on P bioavailability in organic fertilizers produced with different technologies can be used for optimizing fertilization, minimizing build-up of soil P and its adverse environmental effects. • Processing of poultry manure is needed to enhance sustainable use of P. • Bioavailability of P in granulated broiler manure was equal to superphosphate. • Feather meal amendment had minor effects on bioavailability of P in broiler manure. • Slow pyrolysis of broiler manure decreased bioavailability of P. • Granulation and pyrolysis produce poultry manure fertilizers for distinct purposes.

Climate Change Vulnerability and Disaster Risk Assessment Using Remote Sensing Technology and Adaptation Strategies for Resiliency and Disaster Risk Management in Selected Coastal Municipalities of Zambales, Philippines

The Philippines is one of the most hazard prone and vulnerable countries in the world to climate change effects due to its geographical location. Climate change is already happening and affecting many places causing huge problems to coastal ecosystems. Vulnerability and disaster assessment and mapping in coastal areas are essential tasks and undertakings for coastal disaster risk management. The objectives of this study were to assess the climate change vulnerability and disaster risks in the four municipalities (Sta. Cruz, Candelaria, Masinloc and Palauig) of Zambales and to determine the climate change community-based adaptation (CBA) and ecosystem-based adaptation (EBA) strategies. Remote sensing, GIS, secondary data gathering and key informant interview were used to assess vulnerability and disaster risks and mapping in the four municipalities. Survey questionnaire, focus group discussion and key informant interview were utilized in gathering data for the determination of climate change adaptation strategies. Using remote sensing technology, it was revealed that coastline changes have occurred in the shorelines of the four coastal municipalities after a decade. Sea level rise happened in Sta. Cruz and Masinloc, Zambales while there was build-up of soil in the coastline of Candelaria and Palauig, Zambales. Twelve hazard maps, 12 vulnerability maps and 12 disaster risk maps were generated for the three major disasters (flood, landslide, storm surge) in the four coastal municipalities. Based on the flood vulnerability and disaster risk assessment, the municipality of Palauig was found to be the most prone to flooding while the municipality of Candelaria was found to be the most vulnerable to landslide compared to other municipalities. All coastal barangays in the four municipalities were susceptible to storm surge. The four coastal municipalities were conducting community-based adaptation (CBA) and ecosystem-based adaptation (EBA) approaches in order to protect their coastal resources from the damaging impacts of climate change and improve the resilience of their local communities.

Spatial Variability of Soil Phosphorus Indices under Two Contrasting Grassland Fields in Eastern Canada

Phosphorus (P) is an essential nutrient for grassland production systems. However, continuous applications of P fertilizers result in soil P accumulations, increasing the risk of P losses in runoff and erosion. This study aims to investigate the field-scale variability of soil-test P (STP) in two contrasting grassland fields using descriptive statistics and geostatistics for accurate recommendations on soil sampling strategy and sustainable approaches to P management. A young grassland (YG; 2 years) and an old grassland (OG; 10 years under permanent pasture) were classified as humo-ferric podzol and received organic fertilizers. Soil samples were collected in 16-m by 16-m triangular grids at two depths (0–5 and 5–20 cm). They were analyzed for available P and other soil elements extracted using the Mehlich-3 method (M3). The agri-environmental P saturation index (P/Al)M3 was calculated. Phosphorus accumulation was observed in OG (0–5 cm) as a result of long-term manure applications. Repeated applications of organic fertilizers can impact the long-term buildup of soil P, thus decreasing soil P va-riability and spatial dependence in permanent grasslands. A soil sampling strategy focusing on the 0–5 cm layer should be retained in permanent grasslands for sustainable P recommendations in Eastern Canada.

A two-surface thermomechanical plasticity model considering thermal cyclic behavior

In thermal-related engineering such as thermal energy structures and nuclear waste disposal, it is essential to well understand volume change and excess pore water pressure buildup of soils under thermal cycles. However, most existing thermo-mechanical models can merely simulate one heating–cooling cycle and fail in capturing accumulation phenomenon due to multiple thermal cycles. In this study, a two-surface elasto-plastic model considering thermal cyclic behavior is proposed. This model is based on the bounding surface plasticity and progressive plasticity by introducing two yield surfaces and two loading yield limits. A dependency law is proposed by linking two loading yield limits with a thermal accumulation parameter nc, allowing the thermal cyclic behavior to be taken into account. Parameter nc controls the evolution rate of the inner loading yield limit approaching the loading yield limit following a thermal loading path. By extending the thermo-hydro-mechanical equations into the elastic–plastic state, the excess pore water pressure buildup of soil due to thermal cycles is also accounted. Then, thermal cycle tests on four fine-grained soils (natural Boom clay, Geneva clay, Bonny silt, and reconstituted Pontida clay) under different OCRs and stresses are simulated and compared. The results show that the proposed model can well describe both strain accumulation phenomenon and excess pore water pressure buildup of fine-grained soils under the effect of thermal cycles.

Novel wiper device for the management of weedy rice

The research programme undertaken at Rice Research Station, Moncompu, Kerala Agricultural University, for the post-emergence management of weedy rice by direct contact application (DCA) of broad-spectrum non-selective herbicides using specially designed novel hand held weed wiper device could selectively dry the panicles of weedy rice at 60–65 DAS, taking advantage of the height difference of 15–20 cm between weedy rice and cultivated rice. The study revealed that DCA can be effectively done in weedy rice infested cropped field using non-selective herbicides, viz. glufosinate ammonium, paraquat dichloride or glyphosate at 1015% concentration. Weed control efficiency by this method in terms of drying of the weedy rice panicles was as high as 83 to 88%. The device has been filed for Indian Patent at Patent Office, Chennai (Application No. 1763/CHE/2014 dated 01.04.2014). The technology can reduce the seed rain and buildup of soil seed bank of weedy rice. It is highly energy efficient, less labour intensive, and ecofriendly compared to hand weeding, cutting of weedy rice ear heads or application of large quantity of herbicides using sprayers. The device has become popular among the farming community of Kerala and transfer of technology of the device was done during 2015. The product is now marketed as ‘KAU Weed Wiper’ by M/s Raidco Ltd, for large scale manufacturing and sale to farmers.

Nitrogen cycling trade-offs with broadcasting and injecting dairy manure

Understanding the fate of nutrients in land-applied manure is key to improving the efficiency of their use in crop production. We developed nitrogen (N) budgets for 2 years of continuously cropped corn fertilized by dairy manure via broadcast application or shallow disk injection. Major pathways and pools of N loss were monitored on 12, 0.04 ha field lysimeters in central Pennsylvania, USA to estimate the impact of manure application method on N fate: gas emissions, off-site runoff (overland and subsurface flow), crop uptake, and, soil storage. The budgets illuminated trade-offs in N cycling with each management strategy. Crop removal accounted for the largest portions of manure N applied in both budgets (16–43%). Injection manure N balances were more difficult to close because balances included a large proportion of ‘unaccounted’ N (49% and 68% of applied N for two accounting periods). Even so, results point to cumulative differences in nutrient use efficiencies that can be attributed to the greater conservation of ammonia-N with manure injection. There was an apparent build-up of soil N with manure injection that was not observed with broadcast application (in pre sidedress nitrogen test measurements). However, these trends were preliminary; over the two growing seasons covered by this study, these findings did not result in significant differences in corn yield or crop N removal.

Soil-plant nitrogen pools in nectarine orchard in response to long-term compost application

The search for sustainable source of N, the need of soil organic matter restoration, along with the call for recycling of organic wastes has led to a rise of the use of organic fertilizers. The aim of the present experiment was to evaluate: the effectiveness of compost application as a N fertilizer, the impact on N distribution in soil and plant and on tree performances, in a long-term experiment (14 years).The study was carried out in the Po valley, Italy and, since orchard planting (2001), the following treatments were applied: 1. unfertilized control; 2. mineral fertilization; 3. compost at a rate of 5 t DW ha−1 yr−1; 4. compost at a rate of 10 t DW ha−1 yr−1. Soil total N, potentially mineralizable, microbial and extractable N were higher in compost in comparison to mineral (fertilizer). The effect was found both in the row and in the inter-row and the rise of N fractions was evident in the shallowest soil layer of the row. Soil mineral, potentially mineralizable N was increased by mineral (11.1 mg kg−1) and compost 10 (12.4 mg kg−1) fertilization compared with control (6.7 mg kg−1). Vegetative growth and yield were increased in trees treated with mineral and compost 10; moreover, these plants were able to recycle (66.1 and 70.5 kg ha−1 yr−1, respectively) and remobilize (41.5 and 48.7 kg ha−1 yr−1, respectively) a higher amount of N than those of control and compost 5. In conclusion, organic fertilization strategy promoted the buildup of soil N reserve, meaning a capacity of the ecosystem to sequestrate N. The application of compost 10 showed a similar effect on plant growth and production as mineral fertilization, but introduced the advantage of the use of a cheap, renewable waste material, providing a new insight on N fertilization management.

Comment on “In vivo assessment of possible probiotic properties of Bacillus subtilis and prebiotic properties of levan”

With the increase in intensive crop and livestock production, excess application of P as fertilizer and manure contributes to the build-up of soil P levels causing eutrophication. A novel biofilm-based technology was developed to recover and reposition the nutrients in manure, producing biofilm fertilizer and the treated water with better nutrient composition. Anaerobically digested and pretreated manure was used as a medium to grow the surface-attached composite biofilm, which constitutes the selected polyphosphate accumulating fungi and nitrogen accumulating fresh water microalgae for efficient recovery of nutrients on a matrix for better biomass harvesting. Under the tested conditions in lab-scale with the pretreated digested manure, the removal efficiency of the nutrients by attached mycoalgae biofilm was 76.74% P and 76.40% N with COD removal of 65.75%. To increase the nutrient content of the biomass and for enhancing the cell growth the wastewater generated in corn ethanol process (thin stillage) was added as an external nutrient at different ratios in the digested manure. The cell growth, nutrient removal efficiency, lipid content of the biomass, COD removal and reducing sugar content at different medium conditions were evaluated. The nutrient-rich solid biofilm can be harvested by scraping off the biofilm from the matrix and the nutrient lean liquid can be discharged or further used for agriculture. The microbial biofilm assimilates the organic and inorganic components in manure and converts them into cellular constituents together with N-P-K resulting in deposition of manure nutrients in biofilm, which can be directly used as a bio-fertilizer.

Yield responses to P fertilisation of onion (Allium cepa L.) and cabbage (Brassica oleracea Capitata Group L.) in Finland

Finnish data on vegetable crops’ yield responses to phosphorus (P) applications are scarce, but P is usually applied in quantities that meet the crop demand with wide safety margins. We determined yield responses to P fertilisation of onion and cabbage at three sites in 3-year field trials. Only on a sandy loam with low P status did annual P applications give statistically significant yield increases, 7% and 20% over the P-unfertilised treatment for onion and cabbage, respectively. The maximum P rate allowed by national regulation for this soil is 80 kg ha-1, but P rates of 10–12 kg ha-1 were sufficient to produce 97% of the yield maxima. The results strongly suggest that the P demand of the studied vegetables is smaller than previously thought also in a boreal climate. Critical soil test P concentrations for vegetables should be established to avoid unnecessary build-up of soil P that may be uneconomical and elevate the risk for P losses to waterways. However, too few data exist for this at present.

Deposition of manure nutrients in a novel mycoalgae biofilm for Nutrient management

Abstract With the increase in intensive crop and livestock production, excess application of P as fertilizer and manure contributes to the build-up of soil P levels causing eutrophication. A novel biofilm-based technology was developed to recover and reposition the nutrients in manure, producing biofilm fertilizer and the treated water with better nutrient composition. Anaerobically digested and pretreated manure was used as a medium to grow the surface-attached composite biofilm, which constitutes the selected polyphosphate accumulating fungi and nitrogen accumulating fresh water microalgae for efficient recovery of nutrients on a matrix for better biomass harvesting. Under the tested conditions in lab-scale with the pretreated digested manure, the removal efficiency of the nutrients by attached mycoalgae biofilm was 76.74% P and 76.40% N with COD removal of 65.75%. To increase the nutrient content of the biomass and for enhancing the cell growth the wastewater generated in corn ethanol process (thin stillage) was added as an external nutrient at different ratios in the digested manure. The cell growth, nutrient removal efficiency, lipid content of the biomass, COD removal and reducing sugar content at different medium conditions were evaluated. The nutrient-rich solid biofilm can be harvested by scraping off the biofilm from the matrix and the nutrient lean liquid can be discharged or further used for agriculture. The microbial biofilm assimilates the organic and inorganic components in manure and converts them into cellular constituents together with N-P-K resulting in deposition of manure nutrients in biofilm, which can be directly used as a bio-fertilizer.

Land Use Effects on Soil Fertility and Nutrient Cycling in the Peruvian High‐Andean Puna Grasslands

Core Ideas A short‐term increase in fertility and greater N mineralization were found in agricultural lands. Low plant recovery and soil degradation were found in fallow soils correlated with erosion indexes. In grass‐legume mixture pastures, improved soil structure and N build up increased soil fertility. P was found as the limiting nutrient in the studied agroecosystem. Expansion of crop production into high‐altitude native grasslands is occurring in the Peruvian High‐Andes due to climate change and agricultural intensification, with little understanding of the consequences to the ecosystem. The objective of this study was to determine the impact of land‐use changes on soil fertility and nutrient cycling to guide future land management. Comparisons were made between native grasslands and two alternative farming systems; the first was a system in which native grassland was replaced by an annual cash crop, maca (Lepidium meyenii Walp.), followed by a long fallow and the second was a long‐standing perennial cultivated pasture. There was greater N mineralization, extractable Bray‐1 P, and K+ in recently converted maca soils relative to adjacent native grassland soils most likely caused by tillage‐induced nutrient mineralization and by incorporation of manure and native grassland residue during the first year of land preparation prior to planting maca. Soil fertility, as determined by an ex situ pot trial to measure plant yield, was correlated with plant cover, soil total organic carbon, and water stable aggregates (WSA) under fallow following maca, suggesting that soil erosion might be an issue in the long term. In cultivated pastures, we found an increase in long‐term fertility driven primarily by the build‐up of soil N and improved soil structure in the perennial grass‐legume mixture compared with adjacent native grassland. Responsible management of the Puna agroecosystem requires restoration of plant cover after annual cropping of maca or the establishment of mixed perennial cultivated pasture.

Compost Input Effect on Dryland Wheat and Forage Yields and Soil Quality

Organic agricultural systems rely on organic amendments to achieve crop fertility requirements, and weed control must be achieved without synthetic herbicides. Our objective was to determine the crop yield and soil quality as affected by a transition from grass to dryland organic agriculture in the Central Great Plains of North America. This study evaluated three beef feedlot compost (BFC) treatments in 2010–2015 following biennial application rates: 0 (control), 22.9, and 108.7 t ha−1 on two dryland organic cropping systems: a wheat (Triticum aestivum)-fallow (WF) rotation harvested for grain and a triticale (Triticosecale)/pea (Pisum sativum)-fallow (T/P-F) rotation harvested for forage. The triticale + pea biomass responded positively to the 108.7-t ha−1 BFC treatment, but not the 22.9-t ha−1 BFC treatment. The wheat biomass was not affected by BFC addition, but biomass N content increased. Beef feedlot compost input did not increase wheat grain yields, but had a positive effect on wheat grain Zn content. Soil total C and N contents increased with the rate of 108.7 t ha−1 BFC after three applications, but not with 22.9 t ha−1 BFC. Soil enzyme activities associated with N and C cycling responded positively to the 108.7-t ha−1 BFC treatment. Saturated salts were high in the soil receiving 108.7 t ha−1 of BFC, but did not affect crop yields. These results showed that BFC was effective in enhancing forage yields, wheat grain quality, and soil C and N, as well as specific microbial enzymes important for nutrient cycling. However, the large rates of BFC necessary to elicit these positive responses did not increase grain yields, and resulted in an excessive buildup of soil P.

Fertilizer nitrogen recovery efficiencies in crop production systems of China with and without consideration of the residual effect of nitrogen

China is the world’s largest consumer of synthetic nitrogen (N), where very low rates of fertilizer N recovery in crops have been reported, raising discussion around whether fertilizer N use can be significantly reduced without yield penalties. However, using recovery rates as indicator ignores a possible residual effect of fertilizer N—a factor often unknown at large scales. Such residual effect might store N in the soil increasing N availability for subsequent crops. The objectives of the present study were therefore to quantify the residual effect of fertilizer N in China and to obtain more realistic rates of the accumulative fertilizer N recovery efficiency (RE) in crop production systems of China. Long-term spatially-extensive data on crop production, fertilizer N and other N inputs to croplands in China were used to analyze the relationship between crop N uptake and fertilizer N input (or total N input), and to estimate the amount of residual fertilizer N. Measurement results of cropland soil N content in two time periods were obtained to compare the change in the soil N pool. At the provincial scale, it was found that there is a linear relationship between crop N uptake and fertilizer N input or total N input. With the increase in fertilizer N input, annual direct fertilizer N RE decreased and was indeed low (below 30% in recent years), while its residual effect increased continuously, to the point that 40–68% of applied fertilizer was used for crop production sooner or later. The residual effect was evidenced by a buildup of soil N and a large difference between nitrogen use efficiencies of long-term and short-term experiments.

Seeing about soil — management lessons from a simple model for renewable resources

Employing an effective cellular automata model, we investigate and analyze the build-up and erosion of soil. Depending on the strategy employed for handling agricultural production, in many cases we find a critical dependence on the prescribed production target, with a sharp transition between stable production and complete breakdown of the system.Strategies which are particularly well-suited for mimicking real-world management approaches can produce almost cyclic behavior, which can also either lead to sustainable production or to breakdown.While designed to describe the dynamics of soil evolution, this model is quite general and may also be useful as a model for other renewable resources and may even be employed in other disciplines like psychology.

The Phosphorus Footprint of China's Food Chain: Implications for Food Security, Natural Resource Management, and Environmental Quality

Efficient use of phosphorus (P) for producing food, preventing water pollution, and managing a dwindling rock P reserve are major challenges for China. We analyzed P stocks and flows in the Chinese food chain to identify where P use efficiency can be improved, where P leaks to the environment, and the research, technologies, and policies needed to improve P use. We found a high degree of inefficiency; of 6652 Gg P entering the food chain, only 1102 Gg P (18%) exit as food for humans. The greatest inefficiencies were a large build-up of soil P (3670 Gg P yr; 52% of P inputs) and high P losses to the environment from animal production (1582 Gg P yr; 60% of excreted P). Improving P use in China must focus on national-scale nutrient management strategies, better animal nutrition, and adoption of technologies and policies to reduce P discharges from the animal sector and recycle P as manures in agriculture.

Long-term nitrogen additions increased surface soil carbon concentration in a forest plantation despite elevated decomposition

Abstract Forests cover one-third of the Earth’s land surface and account for 30–40% of soil carbon (C). Despite numerous studies, questions still remain about the factors controlling forest soil C turnover. Present understanding of global C cycle is limited by considerable uncertainty over the potential response of soil C dynamics to rapid nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application. Here, we present a 15-year-long field study and show an average increase of 14.6% in soil C concentration in the 0–5 cm mineral soil layer in N fertilized (defined as N+ hereafter) sub-plots of a second-rotation Pinus radiata plantation in New Zealand compared to control sub-plots. The results of 14 C and lignin analyses of soil C indicate that N additions significantly accelerate decomposition of labile and recalcitrant soil C. Using an annual-time step model, we estimated the soil C turnover time. In the N+ sub-plots, soil C in the light (a density −3 ) and heavy fractions had the mean residence times of 23 and 67 yr, respectively, which are lower than those in the control sub-plots (36 and 133 yr in the light and heavy fractions, respectively). The commonly used lignin oxidation indices (vanillic acid to vanillin and syringic acid to syringaldehyde ratios) were significantly greater in the N+ sub-plots than in the control sub-plots, suggesting increased lignin decomposition due to fertilization. The estimation of C inputs to forest floor and δ 13 C analysis of soil C fractions indicate that the observed buildup of surface soil C concentrations in the N+ sub-plots can be attributed to increased inputs of C mass from forest debris. We conclude that long-term N additions in productive forests may increase C storage in both living tree biomass and soils despite elevated decomposition of soil organic matter.

Effect of Land Use Conversion from Rice Paddies to Vegetable Fields on Soil Phosphorus Fractions

Excess phosphorus (P) from agricultural soils contributes to eutrophication in water bodies. Samples ( n = 60) were taken from sites where rice paddies have been converted to vegetable fields for 0, < 10, 10–20, and > 20 years and analyzed for five inorganic P (P i) fractions, three organic P (P o) fractions, and several soil parameters to investigate how land use conversion affects P i and P o fractions in a peri-urban area of China with soils characteristic of many agricultural areas of Asia. Significant increases of 33, 281, 293, and 438 mg kg −1 were found for soluble and loosely bound P i (SL-P i), aluminum-bound P i (Al-P i), calcium-bound P i (Ca-P i), and iron-bound P i (Fe-P i), respectively, after conversion from rice paddies to vegetable fields. Most of the increase in P i was in the form of Fe-P i, which increased from 8% of total P (TP) on paddy soil to 31% on the soil with > 20-year vegetable cultivation, followed by Al-P i, which increased from 2% to 19% of TP. For P o fractions, there was no significant change in P concentrations. The conversion of land use from paddy fields to high intensity vegetable fields was causing significant changes in soil P fractions. Management practices were causing a buildup of soil P, primarily in the Fe-P i fraction, followed by Ca-P i and Al-P i fractions. If current trends continue, a 30%–70% increase in TP could be expected in the next 20 years. Farmers in the area should reduce P application and use to maximize P uptake.