Soil Organic Matter Nitrogen Research Articles

Predicting soil organic matter nitrogen mineralization

AbstractThe objectives of this study were to develop a model for soil organic matter (SOM) N mineralization that required minimal inputs, to test the model using independent datasets, and to determine if the results could be used in adjusting commercial N fertilizer recommendations. A first‐order model was adjusted monthly for differences in soil temperature and moisture. A daily time step was used to allow N mineralization estimates from one date to another. Simulations began in the month where temperature exceeded 10 °C. Model predictions were compared with those in published studies in northern California and Illinois. In the first California study, model predictions were near observed values in four of five locations. In the second California study, model predictions were within the 95% confidence interval of those based on laboratory incubation corrected for field temperature and moisture regimes. In a third study, unfertilized corn (Zea mays L.) yields were compared with seasonal N mineralization predictions plus N from the prior crop for 15 Illinois soils. The result was 32.0 kg corn kg−1 seasonal available N as compared with the typical value of 67.5 kg corn kg−1 commercial N fertilizer. Nitrogen mineralization predictions for Illinois soils were related to total N, suggesting that an equation could replace simulation modeling for a given soil–location combination. It is proposed that the N mineralization model, which has readily obtainable inputs (total N, bulk density, monthly weather), could be used in conjunction with field studies to refine commercial N fertilizer recommendations.

Soil Profile Studies of Organic and Conventional farms growing Chilli, Capsicum annuum

The experiments were conducted to determine effects of farming practises on soil quality of fields. Comparative analyses of soil samples from organic and conventional farms were carried out for soil organic matter nitrogen, phosphorus, potassium, salinity, and soil pH. Applications of organic manures increase the availability of organic elements in soil naturally and improve the Nutrient Use Efficiency (NUE) of crops. Standard chemical analytical methods were used to determine organic matter, EC, pH, in soil. Special attention was paid to phosphorus, nitrogen and potassium. Soil profile analysis showed that organic farming gradually enhances soil quality naturally. Results indicated increasing levels of organic carbon, total nitrogen, phosphorus, potassium, CEC, pH of soil from farms practising organic farming.

Effect of subtilisin, a protease from Bacillus sp., on soil biochemical parameters and microbial biodiversity

Proteinaceous material constitute the main source of nitrogen in soil organic matter. Use of this nitrogen is limited by the breakdown of proteins into peptides and free amino acids. Proteases, therefore, are important in the use of protein N. The aim of this study is to assess the effect of subtilisin, which is a soil extracellular endopeptidase from Bacillus sp., both on soil microbial biostimulation and biodiversity. In addition to the protease, keratins, an insoluble-protein and low-bioavailable substrate, was added to enhance the effect of protease in soil. Protease, both on its own and in combination with keratins, has a biostimulant effect on soil microbial activity that was reflected in the protease, dehydrogenase and phosphatase activities.DNA metabarcoding analysis further revealed specific changes in soil biodiversity, mainly defined by the enrichment of plant-growth promoting microorganisms, specifically those producing hydrolase enzymes such as phosphatase and ammonifiers. Surprisingly, the addition of keratins specifically showed a rapid stimulation of soil proteolytic bacteria.Thus, the present work supports the use of subtilisin as biofertiliser and values the recycling of keratinous industrial waste in the field of biofertilisation.

Strengthening mycorrhizal research in South America.

Strengthening mycorrhizal research in South America.

Simulating phosphorus responses in annual crops using APSIM: model evaluation on contrasting soil types

Crop simulation models have been used successfully to evaluate many systems and the impact of change on these systems, e.g. for climatic risk and the use of alternative management options, including the use of nitrogen fertilisers. However, for low input systems in tropical and subtropical regions where organic inputs rather than fertilisers are the predominant nutrient management option and other nutrients besides nitrogen (particular phosphorus) constrain crop growth, these models are not up to the task. This paper describes progress towards developing a capability to simulate response to phosphorus (P) within the APSIM (Agricultural Production Systems Simulator) framework. It reports the development of the P routines based on maize crops grown in semi-arid eastern Kenya, and validation in contrasting soils in western Kenya and South-western Colombia to demonstrate the robustness of the routines. The creation of this capability required: (1) a new module (APSIM SoilP) that simulates the dynamics of P in soil and is able to account for effectiveness of alternative fertiliser management (i.e. water-soluble versus rock phosphate sources, placement effects); (2) a link to the modules simulating the dynamics of carbon and nitrogen in soil organic matter, crop residues, etc., in order that the P present in such materials can be accounted for; and (3) modification to crop modules to represent the P uptake process, estimation of the P stress in the crop, and consequent restrictions to the plant growth processes of photosynthesis, leaf expansion, phenology and grain filling. Modelling results show that the P routines in APSIM can be specified to produce output that matches multi-season rotations of different crops, on a contrasting soil type to previous evaluations, with very few changes to the parameterization files. Model performance in predicting the growth of maize and bean crops grown in rotation on an Andisol with different sources and rates of P was good (75-87% of variance could be explained). This is the first published example of extending APSIM P routines to another crop (beans) from maize.

Distribution characteristics of soil organic matter and total nitrogen on the Yajiageng vertical belt, Gongga Mountain around the Dadu River banks

Distribution characteristics of soil organic matter(SOM) and total nitrogen(TN) were studied in different plant communities of the Yajiageng vertical belt in Gongga Mountain around the Dadu River banks. The results show: ➀ the contents of SOM and TN of the plant communities gradually decreased with the following order: subalpine coniferous forest (3 027 m), subalpine meadow (3 873 m), coniferous broadleaved mixed forest(2 737 m), subalpine shrub(3 565 m) and treeline(3 564 m). ➁ With soil profile depth increasing, the contents of SOM and TN gradually decreased. For different vegetation types, the contents of SOM and TN in sub-alpine coniferous forest were higher than that of other vegetational types. ➂ The ratio of the content of carbon to the content of total nitrogen (C C/C TN) was 13.5–27.6, which was relatively lower than the appropriate C C/C TN of 25–30, and indicated that the soil in favor of the organic matter decomposed and nutrients released. C C/C TN in the soil had no correlation with sea level altitude. However, its distribution in the soil varied with different vegetation types. ➃ Nitrogen in SOM existed mainly in the form of organic nitrogen, and C C/C TN in the soil was not obvious correlated with SOM and TN.

Effects of potato–grain rotations on soil erosion, carbon dynamics and properties of rangeland sandy soils

The potential for wind erosion in South Central Colorado is greatest in the spring, especially after harvesting of crops such as potato ( Solanum tuberosum L.) that leave small amounts of crop residue in the surface after harvest. Therefore it is important to implement best management practices that reduce potential wind erosion and that we understand how cropping systems are impacting soil erosion, carbon dynamics, and properties of rangeland sandy soils. We evaluate the effects of cropping systems on soil physical and chemical properties of rangeland sandy soils. The cropping system included a small grain–potato rotation. An uncultivated rangeland site and three fields that two decades ago were converted from rangeland into cultivated center-pivot-irrigation-sprinkler fields were also sampled. Plant and soil samples were collected in the rangeland area and the three adjacent cultivated sites. The soils at these sites were classified as a Gunbarrel loamy sand (Mixed, frigid Typic Psammaquent). We found that for the rangeland site, soil where brush species were growing exhibited C sequestration and increases in soil organic matter (SOM) while the bare soil areas of the rangeland are losing significant amounts of fine particles, nutrients and soil organic carbon (SOM-C) mainly due to wind erosion. When we compared the cultivated sites to the uncultivated rangeland, we found that the SOM-C and soil organic matter nitrogen (SOM-N) increased with increases in crop residue returned into the soils. Our results showed that even with potato crops, which are high intensity cultivated cropping systems, we can maintain the SOM-C with a rotation of two small grain crops (all residue incorporated) and one potato crop, or potentially increase the average SOM-C with a rotation of four small grain crops (all residue incorporated) and one potato crop. Erosion losses of fine silt and clay particles were reduced with the inclusion of small grains. Small grains have the potential to contribute to the conservation of SOM and/or sequester SOM-C and SOM-N for these rangeland systems that have very low C content and that are also losing C from their bare soils areas (40%). Cultivation of these rangelands using rotations with at least two small grain crops can reduce erosion and maintain SOM-C and increasing the number of small grain crops grown successfully in rotation above two will potentially contribute to C and N sequestration as SOM and to the sequestration of macro- and micro-nutrients.

Missing sinks, feedbacks, and understanding the role of terrestrial ecosystems in the global carbon balance

Terrestrial ecosystems are thought to be a major sink for carbon at the present time. The endeavor to find this terrestrial sink and to determine the mechanisms responsible has dominated terrestrial research on the global carbon cycle for years. Some of the mechanisms advanced to explain the “missing sink” are also negative feedbacks to a global warming. Here we distinguish between mechanisms likely to act as feedbacks to a global warming and other mechanisms consistent with a terrestrial sink that are not feedbacks to a global warming. One of the postulated negative feedback mechanisms that also helps explain the current “missing sink” is based on the theory that carbon should accumulate in vegetation as a result of a warming‐enhanced mineralization of nitrogen in soil organic matter. The theory assumes that mineralized N is neither retained in the soil (through reimmobilization by microbial biomass) nor lost from the ecosystem, but rather becomes available for plant growth. None of these assumptions is supported yet by field data. In contrast, trends across existing climatic gradients suggest that warmer temperatures will lead to a decrease in the C:N ratio of soils (i.e., the mineralized N remains in soil). Data pertaining to temporal variability in the global carbon balance are conflicting with respect to the question of whether increasing temperatures cause a release or storage of terrestrial carbon. The answer seems to depend in part on time scale. Most likely, multiple mechanisms, including some that release carbon and others that accumulate it, account for the present net accumulation of carbon on land. However, a positive feedback between temperature and the release of CO2to the atmosphere by terrestrial respiration seems likely to grow in importance and could change significantly the role that terrestrial ecosystems play in the global carbon balance.

Treedyn3 forest simulation model

The treedyn3 forest simulation model is a process model of tree growth, carbon and nitrogen dynamics in a single-species, even-aged forest stand. It is based on the treedyn model. Major changes include the computation of sun angle and radiation as a function of latitude and day of the year, the closed-form integration of canopy production as a function of day and hour, the introduction of tree number, height, and diameter as separate state variables, and different growth strategies, mortalities, and resulting self-thinning as function of crowding competition. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: tree number, base diameter, tree height, wood biomass, nitrogen in wood, leaf mass, fine root mass, fruit biomass, assimilate, carbon and nitrogen in litter, carbon and nitrogen in soil organic matter, and plant-available nitrogen. The model includes explicit formulations of all relevant ecophysiological processes such as: computation of radiation as a function of seasonal time, daytime and cloudiness, light attenuation in the canopy, and canopy photosynthesis as function of latitude, seasonal time, and daytime, respiration of all parts, assimilate allocation, increment formation, nitrogen fixation, mineralization, humification and leaching, forest management (thinning, felling, litter removal, fertilization etc.), temperature effects on respiration and decomposition, and environmental effects (pollution damage to photosynthesis, leaves, and fine roots). Only ecophysiological parameters which can be either directly measured or estimated with reasonable certainty are used. treedyn3 is a generic process model which requires species- and site-specific parametrization. It can be applied to deciduous and coniferous forests under tropical, as well as temperate or boreal conditions. The paper presents a full documentation of the mathematical model as well as representative simulation results for spruce and acacia.

Case Studies on Nitrate Leaching in Arable Fields of Organic Farms

ABSTRACT Nitrogen supply of crops on organic farming systems mainly depends on mineralization of soil organic matter nitrogen. Mineralization was studied by taking soil samples from 30 plots in the crop rotation of two organic farms at intervals of 7 to 14 days during the growing season. On fallow plots net-mineralization alternated with net-immobilization three times from April to November. These soil inherent dynamics were modified by cultivation and the growing cycles of the different crops. Several cases could be observed which led to high accumulations of leacheable nitrate in soils: 1. fallow during growing season, 2. fallow during autumn and winter, 3. manuring in autumn, 4. leaching of chopped green manure by rain, 5. low nitrogen uptake of crops because of diseases, 6. transfer of mineralizable nitrogen from spring to autumn. The concept of the soil merely as a storage place for plant nutrients was one of the main factors for mistakes in nitrogen management. Understanding the interactions of plan...

Complex dynamics in a carbon-nitrogen model of a grass-legume pasture

A physiologically based model of a grass-legume pasture is used to study the dynamics of these competing species. In our model, we consider carbon and nitrogen pools and fluxes, incorporating competition for light and soil mineral nitrogen, and including the processes of nitrogen fixation, nitrogen losses and dry matter allocation. First, the steadystate responses of each species to nitrogen deposition, to leaching rate, and to other nitrogen losses are examined. We then consider the dynamic behaviour of these species when there is no time delay for nitrogen cycled through the soil organic matter pool. Next, the effects of various time delays associated with the soil organic matter nitrogen pool on the system dynamics are examined: the behaviour becomes complex, non-linear and exhibits lightly or heavily damped oscillations at two frequencies. The high sensitivity of the system both to the initial value of the soil organic matter nitrogen pool, and to any photosynthetic competitive advantage, is investigated. The implications of these results in relation to observations and experiments on grass-legume pastures are discussed.

Natural abundance of 15N in soils along forest-to-pasture chronosequences in the western Brazilian Amazon Basin.

We examined the natural abundance of 15N in soil profiles along two chronosequences in the western Brazilian Amazon Basin state of Rondônia, to investigate possible mechanisms for changes to soil nitrogen sources and transformations that occur as a result of land use. One chronosequence consisted of forest and 3-, 5- and 20-year-old pasture, the other of forest and 8- and 20-year-old pasture. The δ15N values of surface soil and soil to 1 m depth in the native forest ranged from 9.8 to 13.6‰ and were higher than reported for temperate forest soils. Fractionation associated with nitrification and denitrification and selective losses of 15N-depleted nitrate, could potentially result in a strong enrichment of nitrogen in soil organic matter over the time scale of soil development in highly weathered tropical soils. Pasture surface soils were 1-3‰, depleted in 15N compared with forest soils. Lower δ15N values in 20-year-old pastures is consistent with greater cumulative inputs of 15N-depleted atmospheric-derived nitrogen, fixed by free-living bacteria associated with planted pasture grasses in older pastures, or differential plant utilization of soil inorganic N pools with different δ15N values. The pattern of δ15N values following conversion of forest to agricultural use differs from the pattern in the temperate zone, where pasture or cultivated soils are typically more enriched in 15N than the forest soils from which they were derived.

Decomposition and Nutrient Release Patterns of the Leaves of Three Tropical Legumes

Information on decomposition and nitrogen release patterns of tropical legumes is scarce despite the important role of legumes in agroforestry systems. Decomposition patterns of the leaves of three tropical legumes Inga edulis Mart., Cajanus cajan (1.) Millsp., and Erythrina sp. were determined by a litterbag study in an alley cropping experiment conducted in the Peruvian Amazon. The leaflets of the three species had similar nitrogen concentrations but different lignin and soluble polyphenolic concentrations. Inga and Cajanus decomposed at similar rates (k = 0.91 and 1.72 yr-1, respectively) and had similar polyphenolic concentrations but differed in lignin. Erythrina had the lowest concentration of polyphenolics and decomposed the fastest (k = 3.45 yr-1). Polyphenolics appeared to influence rates of decomposition more than percent nitrogen or percent lignin. It is proposed that the polyphenolics bind to N in the leaves forming compounds resistant to decomposition. These compounds may be precursors to stable forms of nitrogen in soil organic matter. Rates of nutrient loss followed the general trend potassium > phosphorus, nitrogen, and magnesium > calcium. It is apparent from this study that not all leguminous leaves decompose and release nitrogen quickly, despite high nitrogen concentrations in the leaves. Nitrogen release by legumes with high polyphenolic concentrations will be slower than that by legumes with low polyphenolic concentrations and has important implications to nitrogen cycling and the selection of legumes for agroforestry systems.

Generic simulation model of forest growth, carbon and nitrogen dynamics, and application to tropical acacia and european spruce

Abstract In order to provide accurate assessments of forest stand development even in the absence of long-term growth and yield observations (as may be the case in developing countries and for less well-known species), a generic dynamic (cybernetic) simulation model has been developed representing tree growth, and carbon and nitrogen dynamics in a single-species, even-aged forest stand. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: wood, leaf, fine root, fruit biomass; assimilate; carbon and nitrogen in litter; carbon and nitrogen in soil organic matter; and plant-available nitrogen. All parameters are measurable ecophysiological quantities (no statistical parameter estimation). The model includes explicit formulations of all relevant ecophysiological processes such as: temporal and spatial light distribution and photosynthesis in the canopy; respiration of all parts; assimilate allocation; increment formation; nitrogen fixation, mineralization, humification and leaching; forest management (thinning, felling, litter removal, fertilization, etc.); and environmental effects (air pollution and insect damage). Application of the model requires specification of 38 tree-specific and 15 region-specific parameters (obtainable - except for root data - from simple field estimates or laboratory measurements not requiring time-series studies), 10 initial conditions for the state variables and 13 scenario parameters (e.g. nitrogen input, maximum nitrogen-fixing rate, litter removal, thinning and cutting schedule, pollution damage to photosynthesis, leaves, or fine roots, time and severity of insect calamity). The simulation model has been applied successfully to study stand growth behavior under different conditions of soil quality, forest management, and pollution and insect damage for broadleaf trees in a tropical climate ( Acacia auriculaeformis ) Cunn. ex Benth. in South China) and coniferous trees in a temperate climate ( Picea abies (L.) Karst. in Central Europe). Despite the difference of species and climate, the model provides accurate representations of stand development under various conditions in both cases, yielding good agreement with standard yield tables (for spruce).