Inorganic Nitrogen Application Research Articles

Linking organic carbon accumulation to microbial community dynamics in a sandy loam soil: result of 20 years compost and inorganic fertilizers repeated application experiment

Repeated compost or inorganic fertilization may increase soil organic C (SOC) but how SOC accumulation relates to changes in soil aggregation, microenvironment and microbial community structure is unclear. Arable soils (Aquic Inceptisol) following a 20-year (1989–2009) application of inorganic fertilizer nitrogen (N), phosphorus (P) and potassium (K) (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK), compost (CM), half compost N plus half fertilizer N (HCM), and non-fertilization (Control) were collected to evaluate the relationship between SOC accumulation rate, soil aggregation, microenvironment and microbial community composition using phospholipid fatty acid (PLFA) analysis. Compared to the starting year, SOC content after 20 years under CM, HCM and NPK was significantly (P < 0.05) increased by 172 %, 107 % and 56 %, respectively, and by less than 50 % under NP, NK and PK. The mass proportion of macroaggregates was increased by 101–250 % under CM, but was not significantly affected by inorganic fertilizations, except PK. Compost and NPK significantly (P < 0.05) reduced the effective diffusion coefficient of oxygen primarily by increasing the proportion of pores <4 μm, and in contrast, increased the abundance of branched PLFAs and Gram-positive (G+) bacteria, resulting in the reduction of the ratio of monounsaturated/branched PLFAs (M/B) compared with Control. The mass proportion of macroaggregates was significantly (P < 0.01) and negatively correlated with the effective diffusion coefficient of oxygen; the latter was positively associated with M/B ratio. The SOC accumulation rate (z) had a significant interaction with the mass proportion of macroaggregates (x) and M/B ratio (y) (z = 0.514 + 4.345e x-15–0.149e y ). Our results suggested that SOC accumulation promoted the macroaggregation and reduced the effective diffusion coefficient of oxygen, causing changes in microhabitats and a shift in microbial community composition to more facultative and/or obligate anaerobes; such microbial community shifts favored accumulation of SOC in turn.

Effects of Long‐Term Fertilization on Soil Carbon and Nitrogen in Chinese Mollisols

Three field experiments were conducted to examine the influence of long‐term (30–31 yr) effect of fertilizer applications on soil C and N in the mollisols of Northeast China. Each experiment represented a different latitude range: low latitude (LatL), middle latitude (LatM) and high latitude (LatH). Four types of fertilizer applications were considered: (i) CK: unfertilized (control); (ii) NPK: balanced application of inorganic fertilizer nitrogen, phosphorus, potassium; (iii) M: application of organic manure; and (iv) NPKM: fertilizer nitrogen, phosphorus, potassium, plus organic manure. Compared with CK treatments, applications of fertilizers increased soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), microbial biomass carbon (Cmic) and microbial biomass nitrogen (Nmic). On average compared with CK treatments, SOC in the NPK, M, and NPKM treatments increased by 2.74, 22.00, and 27.81%, respectively. Thus, applications of organic manure combined with inorganic fertilizers showed greater effects on the topsoil C and N content than inorganic fertilizers. Under the same fertilizer treatments, SOC, TN, Nmic, and Cmic contents were the lowest at LatM site. Available N content decreased for a latitude sequence of LatH &gt; LatM &gt; LatL for CK, M, and NPKM treatments and LatM &gt; LatH &gt; LatL for the NPK treatments. These results indicate that the magnitude of soil C and N among the three sites was not related to the latitude of the experiments.

Initial decomposition of post-harvest crown and root residues of poplars as affected by N availability and particle size

An incubation experiment was carried out to investigate the impacts of residue particle size and N application on the decomposition of post-harvest residues of fast-growing poplar tree plantations as well as on the microbial biomass. Crown and root residues, differing in their C/N ratios (crown 285, root 94), were ground to two particle sizes and incubated with and without application of inorganic nitrogen (N) for 42 days in a tilled soil layer from a poplar plantation after 1 year of re-conversion to arable land. Carbon and N mineralization of the residues, microbial biomass C and N, ergosterol contents, and recovery of unused substrate as particulate organic matter (POM) were determined. Carbon mineralization of the residues accounted for 26 to 29 % of added C and caused a strong N immobilization, which further increased after N addition. N immobilization in the control soil showed that even 1 year after re-conversion, fine harvest residues still remaining in the soil were a sink for mineral N. Irrespective of the particle size, C mineralization increased only for crown residues after application of N. Nevertheless, the overall decrease in amounts of POM-C and a concurrent decrease of the C/N ratio in the POM demonstrate the mineralization of easily available components of woody residues. Microbial biomass significantly decreased during incubation, but higher cumulative CO2 respiration after N application suggests an increased microbial turnover. Higher ergosterol to microbial biomass C ratios after residue incorporation points to a higher contribution of saprotrophic fungi in the microbial community, but fungal biomass was lower after N addition.

Soil type, crop and irrigation technique affect nitrogen leaching to groundwater

Many groundwater resource in California are degraded by high concentrations of nitrate, most of which was transported to the groundwater in water percolating below the root zone of agricultural fields. Factors that affect the rate of water percolation — including soil type, crop and irrigation — along with nitrogen application influence the probability of this type of groundwater degradation. UC scientists have developed several useful tools, including the Nitrogen Hazard Index (NHI) and the ENVIRO-GRO (E-G) model, for use in developing best management practices (BMPs) to achieve high crop yields while minimizing groundwater degradation. We report the results of E-G simulations that quantify the effects of irrigation, soil type and organic and inorganic nitrogen (N) application amounts to corn yield and the amount of leached N. Simulation results indicate that a nitrate management strategy that also includes water management will be more effective in reducing N loading to groundwater. The research findings are discussed in the context of the track and report concept in comparison to the BMP approach.

Differential responses of system of rice intensification (SRI) and conventional flooded-rice management methods to applications of nitrogen fertilizer

Rising food demand, slowing productivity growth, poor N-use efficiency in rice, and environmental degradation necessitate the development of more productive, environmentally-sound crop and soil management practices. The system of rice intensification (SRI) has been proposed as a methodology to address these trends. However, it is not known how its modified crop-soil-water management practices affect efficiency of inorganic nitrogen applications. Field experiments investigated the impacts of SRI management practices with different N-application rates on grain yield, root growth and activity, uptake of N and its use-efficiency, leaf chlorophyll content, leaf N-concentration, and photosynthetic rate in comparison with standard management practices for transplanted flooded rice (TFR). Overall, grain yield with SRI was 49 % higher than with TFR, with yield enhanced at every N application dose. N-uptake, use-efficiency, and partial factor productivity from applied N were significantly higher in SRI than TFR. Higher leaf nitrogen and chlorophyll contents during the ripening-stage in SRI plants reflected delayed leaf-senescence, extension of photosynthetic processes, and improved root-shoot activities contributing to increased grain yield. Rice grown under SRI management used N fertilizer more efficiently due to profuse root development and improved physiological performance resulting in enhanced grain yield compared to traditional flooded rice.

Growth of ectomycorrhizal fungal mycelium along a Norway spruce forest nitrogen deposition gradient and its effect on nitrogen leakage

Almost all boreal and temperate forest tree species live in symbiosis with ectomycorrhizal fungi (EMF); the trees transfer carbon (C) to the fungi in exchange for nutrients and water. Several studies have shown that experimental application of inorganic nitrogen (N) represses production of EMF extramatrical mycelia (EMM), but studies along N deposition gradients are underrepresented. Other environmental variables than N may influence EMM production and in this study we included 29 thoroughly monitored Norway spruce stands from a large geographical region in Sweden in order to evaluate the importance of N deposition on EMM growth and N leaching in a broader context. It was concluded that N deposition was the most important factor controlling EMM production and that the amounts typically deposited in boreal and boreo-nemoral regions can be sufficient to reduce EMM growth. Other factors, such as phosphorus status and pH, were also correlated with EMM production and should be considered when predicting EMM growth and N leaching. We also showed that EMM production substantially contributed to the C sequestration (320 kg ha−1 yr−1), suggesting that it should be included in C cycle modelling. Furthermore, EMF are probably important for the N retention capacity since high N leaching coincided with low EMM growth. However, it was not possible to differentiate between the effects of EMF and the direct effect of N deposition on N leaching in the present study.

The potential to reduce the risk of diffuse pollution from agriculture while improving economic performance at farm level

Abstract Within the constraints of the EU Nitrates and Water Framework Directives, controlling and managing nutrient transfers to water from excessive nutrient use on agricultural land is a significant environmental policy challenge. This paper assesses whether there is room to reduce inorganic nitrogen and phosphorus fertiliser applications and imported feeds by exploring the extent to which application rates may have exceeded optimum levels using data envelopment analysis methodology. The investigation concentrates on specialist dairy and tillage farms in the Republic of Ireland stratified by land use potential as these agricultural systems are the most intensive and may pose the greatest risk in terms of managing nutrient transfers from agricultural land to water bodies. Results demonstrate inefficiency in the utilisation of nitrogen and phosphorus fertilisers across these systems. Second stage regression analysis indicates significant return to efficiency from agricultural education. Average over application of chemical fertilizers ranged from 22.8 to 32.8 kg N ha −1 and 2.9 to 3.51 kg P ha −1 in 2008 which research has shown is at least similar and greater than losses to leaching and runoff for N and P, respectively, from similar intensive agricultural land uses. Potential cost savings on chemical fertilisers across all systems on average ranged from €38.9 ha −1 to €48.5 ha −1 . Additionally, potential cost reductions on imported feeds of €65–84 per livestock were indicated for dairy farms versus efficient cohort benchmark farms. Average excess of imported feedstuffs equated to 5.82–7.44 kg LU −1 of N and 0.92–1.17 kg LU −1 of P. Such reductions have the potential to deliver a double dividend by reducing the risk of diffuse nutrient losses from agricultural land while improving economic margins at farm level.

Long-term fertilization effects on yield trends and soil properties under a winter wheatsummer maize cropping system

This study examined yield trends and changes in soil chemical properties during a 26-year field experiment, involving a winter wheat–summer maize rotation on a loessial soil in China. Mean yields of wheat and maize increased significantly with increasing rates of manure (M) or inorganic nitrogen and phosphorus (NP) application. However, over time, the yield of both crops declined under the NP treatments, although the change was only significant for wheat. Positive yield responses for both crops were recorded under M+NP treatments. Soil organic matter and soil total N increased under all treatments. The Olsen P level dropped significantly in NP plots and increased markedly in manured plots. There was a reduction in soil exchangeable potassium under nearly all treatments, particularly on NP, where it dropped from an initial concentration of 245 mg kg-1 to ca. 110 mg kg-1. We conclude that annual inputs of NP fertilizers at rates of less than 240 kg ha-1 N and 52 kg ha-1 P were not sufficient to sustain crop production in the system investigated. The practice of applying organic manure as well as NP should be modified to facilitate continued crop production and to provide environmental protection. Key words: Chemical fertilizer, organic manure, soil organic matter, Olsen P, soil exchangeable potassium.

Greenhouse gas fluxes respond to different N fertilizer types due to altered plant-soil-microbe interactions

The application of inorganic nitrogen (N) fertilizers strongly influences the contribution of agriculture to the greenhouse effect, especially by potentially increasing emissions of nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) from soils. The present microcosm-study investigates the effect of different forms of inorganic N fertilizers on greenhouse gas (GHG) emissions from two different agricultural soils. The relationship between greenhouse gas emissions and soil microbial communities, N transformation rates and plant (Hordeum vulgare L. cv. Morex) growth were investigated. Repeated N fertilization led to increased N2O emissions. In a parallel survey of functional microbial population dynamics we observed a stimulation of bacterial and archaeal ammonia oxidisers accompanied with these N2O emissions. The ratio of archaeal to bacterial ammonium monooxygenase subunit A (amoA) gene copies (data obtained from Inselsbacher et al., 2010) correlated positively with N2O fluxes, which suggests a direct or indirect involvement of archaea in N2O fluxes. Repeated N fertilization also stimulated methane oxidation, which may also be related to a stimulation of ammonia oxidizers. The fertilizer effects differed between soil types: In the more organic Niederschleinz soil N-turnover rates increased more strongly after fertilization, while in the sandy Purkersdorf soil plant growth and soil respiration were accelerated depending on fertilizer N type. Compared to addition of NH 4 + and NO 3 − , addition of NH4NO3 fertilizer resulted in the largest increase in global warming potential as a summary indicator of all GHG related effects. This effect resulted from the strongest increase of both N2O and CO2 emission while plant growth was not equally stimulated, compared to e.g. KNO3 fertilization. In order to decrease N losses from agricultural ecosystems and in order to minimize soil derived global warming potential, this study points to the need for interdisciplinary investigations of the highly complex interactions within plant-soil-microbe-atmosphere systems. By understanding the microbial processes underlying fertilizer effects on GHG emissions the N use efficiency of crops could be refined.

The effects of organic and inorganic fertilizer applications to Miscanthus×giganteus, Arundo donax and Phalaris arundinacea, when grown as energy crops in Wales, UK

AbstractTwo pot trials and one field trial were established to investigate the effects of organic and inorganic fertilizer applications to energy crops grown in mid‐Wales. Chicken litter and sewage cake applied at a high level in excess of MAFF recommendations produced an increased yield response in Miscanthus and Arundo plants. Miscanthus plants exhibited an increased growth response to all fertilizers applied in its second year. Fertilizer applications in accordance with MAFF recommendations produced no significant differences in yields for Miscanthus or Arundo potted plants. In the field there was an increased yield response of Miscanthus to inorganic nitrogen applications compared with organic manures, but not with control plots. Analysis of the Miscanthus plant material at harvest showed significant differences in the nitrogen, potassium and copper content between treatments. No mineral content differences were shown for Miscanthus rhizome material or Arundo plant material. The Phalaris plants did not exhibit significant differences in growth or yield parameters, but their plant matter showed differences in nitrogen, phosphorus, potassium, calcium, sulphur and boron content between treatments.

Effect of frequency of application of inorganic nitrogen fertilizer within a rotational paddock‐grazing system on the performance of dairy cows and inputs of labour

AbstractAs herd sizes and labour costs increase, and the availability of skilled labour decreases, efficient use of available labour becomes more important in dairy cow systems. Two experiments were conducted to examine the effect of reducing the frequency of application of inorganic nitrogen (N) fertilizer on inputs of labour and performance of dairy cows. Experiments 1 (duration of 169 d) and 2 (duration of 179 d) involved fifty‐eight and forty multiparous Holstein–Friesian dairy cows, respectively, in mid‐lactation. In each experiment, in the ‘infrequent’ treatment fertilizer was applied to all paddocks on a single occasion at the start of each grazing cycle, while in treatment ‘frequent’, fertilizer was applied on three occasions each week, within 2 or 3 d of each paddock having been grazed. The experimental treatments were started from 30 March and 29 March in Experiments 1 and 2 respectively. Total N application rates were approximately 360 and 250 kg N ha−1 in Experiments 1 and 2 respectively. Concentrate feed (4·0 kg per cow) was offered daily in both experiments. With the ‘infrequent’ treatment, highest concentrations of crude protein and nitrate in herbage were observed in swards grazed approximately 10 d after N fertilizer was applied. Treatment had no significant effect on milk yield, milk fat and protein concentrations, and final live weight and body condition score of cows in either experiment. Milk urea and plasma urea concentrations were not significantly affected by treatment. Calculated application times of fertilizer for a herd of 100 dairy cows were 107 and 83 min week−1 for the ‘frequent’ and ‘infrequent’ treatments respectively.

Transformation in soil and availability to plants of &lt;sup&gt;15&lt;/sup&gt;N applied as inorganic fertilizer and grass residue

A pot experiment was conducted in the glasshouse at the Imperial College at Wye to study the transformations that occur following application of both inorganic and organic nitrogen (N) leading to availability to maize and losses into the environment. Organic N was applied as winter rye residue at the rate of 20 g per pot, whilst inorganic N was applied as double-labeled 15NH415NO3 (5 atom %) at the rate of 100 and 200 kg ha-1. Watering was done when the soil began to dry up. Results indicate that N uptake by maize was affected by the rate and source of N application. Seventy-nine days after fertilizer application, 33 % of the N applied at 100 kg ha-1 was recovered in maize, but this was reduced to 24 % when the N application rate was doubled. Of the total N applied in the enriched rye residue, maize N recovery was 20.9 %, soil recovery was 53.2 %, and 0.002 % was lost through N2O emission. By difference, the amount unaccounted for, 25.89 %, was presumably either leached out of the pots and/or incorporated into the soil microbial biomass.

Modeling the Nitrogen and Phosphorus Inputs and Outputs of Financially Optimal Irish Beef Production Systems

Challenges currently faced by beef producers in Ireland include reducing their adverse environmental impact and maintaining farm economic margins. Fertilizers are essential for productive farming but they can be harmful to the environment when inappropriately or excessively applied to crop and pasture land. A linear programming model was used to identify financially optimal strategies for calf-to-stocker and calf-to-finish beef cattle production in high- and low-price market scenarios. The high-price scenario resulted in an increase in gross margin of $1,700 and $13,000 on a 40-ha farm for the stocker and finisher options, respectively. The impacts of these systems on environmental indicators were investigated through farm simulation. In general, the high-price scenarios were more intensive and had greater environmental impacts when compared to the low-price scenarios. Nitrogen leaching losses were quantitatively the most important environmental indicator on well-drained soils with a maximum annual loss of 72 kg N/ha. Volatilization and denitrification losses of nitrogen (N) were also relatively high where more intensive production was practiced with annual losses of 48 and 23 kg N/ha, respectively, in the most intensive scenario identified. Predicted phosphorus losses were small although annual accumulations in the soil of up to 7.5 kg P/ha may lead to greater losses in the future. On poorly drained soils, volatilization losses were greatest with leaching losses in this case the lowest of the loss pathways investigated. Further reduction in inorganic nitrogen application has the potential to reduce N losses, but predicted concomitant reductions in farm gross margins were also considerable.

The impacts of inorganic nitrogen application on mineralization of 14C-labelled maize and glucose, and on priming effect in saline alkaline soil

Organic matter dynamics and nutrient availability in saline alkaline soil of the former lake Texcoco will determine the success of a planned reforestation program. Uniformly labelled 14C-maize (MAI-treatment) and glucose (GLU-treatment) with or without 200 mg NH 4 + − N kg −1 soil (MAI-N treatment and GLU-N treatment, respectively) were added to soils with electrolytic conductivity (EC) 56 dS m −1 (soil A) and 12 dS m −1 (soil B) to investigate the importance of N availability on decomposition of organic material. Production of CO 2 and CO 2 14 and inorganic N dynamics were monitored. The amount of 14C-glucose mineralized increased 1.8-times in the soil A, but had no effect in the soil B when 200 mg NH 4 + − N kg −1 soil was added, while the amount of 14C-maize mineralized increased 1.7 and 1.3-times when 200 NH 4 + − N kg −1 soil was added in the soils A and B, respectively. Application of NH 4 + increased priming effect 3.7-times in the MAI-treatment of the soil A and 3.4-times in the GLU-treatment, while in the soil B the increase of priming effect was 4.1-times in the MAI-treatment and 3.7-times in the GLU-treatment. Of the 200 mg NH 4 + − N kg −1 added to both soils less than 10 mg NH 3–N kg −1 was volatilized within one day, while 22 and 44 mg NH 4 + − N kg −1 soil was fixed on the soil matrix in the soil A and the soil B, respectively. Therefore more than 100 mg NH 4 + −N kg −1 was immobilized into the microbial biomass within the first day. Concentration of nitrite ( NO 2 − ) increased sharply in all the treatments of soil A at the onset of the incubation followed by a decrease. A similar pattern was observed in the GLU-N and MAI-N treatments of the soil B, but not in the other treatments. A decrease in concentration of NO 3 − was observed in both soils followed by an increase in the MAI-N and GLU-N treatments of the soil B. It was found that application of NH 4 + had a stimulating effect on the decomposition of maize and glucose, and on the priming effect, while assimilatory reduction of NO 3 − resulted in an increase of NO 2 − in the soil A, and nitrification in the soil B.

Effect of Organic and Inorganic Fertilizer Application on Maize Fodder Production

The field experiment was conducted at Students Experimental Farm, Sindh Agriculture University Tandojam, Pakistan to assess the maize growth and fodder yield under varying combinations of organic manure (Farm Yard Manure (FYM) at the rate of 1500, 3000 and 4500 kg ha-1) and inorganic fertilizers (0, 60, 90,120 and 150 kg N ha-1). The results revealed that all the maize plant parameters were significantly affected with the incorporation of FYM and nitrogen levels. Among the plant characters, tall plants, maximum stem girth, more green leaves and highest maize fodder yield were observed with the application of 120 kg N ha-1 with combination of 3000 FYM. It was concluded that the inorganic nitrogen application is the common practice of the farmers, but if, farmyard manure will be supplemented there may be significant increase in maize fodder yield.

Above- and below-ground responses of Eragrostis and Bouteloua grass seedlings to the plant-growth-promoting bacterium Azospirillium brasilense

Two experiments were performed to determine the effects of inoculation with N 2 fixing bacterium Azospirillum brasilense on forage production and root growth in seedlings of Wilman lovegrass, weeping lovegrass, and sideoats grama. Two sources of inorganic nitrogen (N) were tested: Urea, CO(NH 2) 2 (45%) and ammonium nitrate NH 4NO 3 (33.3%). Crude protein (CP), calcium (Ca) and phosphorous (P) concentrations were determined. In both experiments top dry matter (DM) production was significantly affected for grasses and inoculation but no differences were found for inorganic nitrogen applications. Maximum amount of top DM was obtained with the Wilman lovegrass with 5.70 g, weeping lovegrass reached 2.70 g, and sideoats grama only reached 1.58 g. Inoculated treatments reached 3.37 g while the no-inoculated treatments obtained 2.74 g. A similar trend was also noted for root phytomass. CP, Ca and P concentrations for the first experiment did not show any trend; therefore, they were not determined for the second experiment. Inoculation of grasses with A. brasilense may be a feasible practice for seeding some rangeland where N deficiency is a problem.

Seven years of biosolids versus inorganic nitrogen applications to tall fescue.

Repeated applications of municipal wastewater biosolids is cost effective for biosolids managers, but may lead to undesirable accumulations of nutrients or contaminants. We evaluated the effects of seven years of biosolids applications on tall fescue (Festuca arundinacea Schreb.) production and nutrient availability. We compared two types of Class A biosolids applied to tall fescue on a sandy loam in western Washington. Mean annual biosolids rates of 290, 580, and 870 kg total N ha(-1) yr(-1) were compared with inorganic N and zero-N controls using a randomized complete block design. We measured yield and N uptake for each forage harvest, plant tissue metals at selected harvests, soil nitrate each fall, diethylenetriaminepentaacetic acid (DTPA)-extractable metals after five years of applications, and soil pH, available P, and organic C after seven years. Forage yields increased with biosolids rate. Apparent nitrogen recovery (ANR) for biosolids averaged 18% in 1993 (Year 1), 35% in 1994, and 46% in 1999. The ANR for inorganic N averaged 62% from 1994-1999. Residual soil nitrate was less than 25 kg ha(-1) for all treatments through 1995, but increased beginning in 1996 for the high biosolids rate. Biosolids increased soil organic C levels by 2 to 5 g kg(-1) and Bray-1 P levels by 300 to 600 mg kg(-1) (0-15 cm depth). Plant tissue Zn increased from 24 to 66 mg kg(-1) at the highest application rate. Nearly all of the DTPA-extractable metals remained in the 0- to 8-cm soil depth.

The effect of three or five years of set-aside on the husbandry and grain yield of subsequent cereal crops in the UK.

During the period 1993–1997, at six contrasting sites located throughout England, two successive cereal test crops were grown both with and without nitrogen fertiliser after three or five years of set-aside or after continuous arable cropping. Vegetation during set-aside included natural regeneration and perennial rye-grass (Lolium perenne) with or without white clover (Trifolium repens), managed by mowing on one or more occasions per year. Establishment of the successive cereal test crops after destruction of the set-aside was generally not a problem. Fertile tiller numbers were increased by inclusion of clover in the set-aside cover or application of inorganic nitrogen. The presence of couch grass (Elytrigia repens) or volunteer cereals in the set-aside covers provided alternative hosts for take-all (Gaeumanomyces graminis) and eyespot (Pseudocercosporella herpotrichoides) and take-all caused some yield reductions in following cereal crops. Management during the set-aside period significantly affected grain yields of the subsequent cereal crops in the majority of the site-year combinations. However, these effects were not as large as would be expected after traditional break crops and were frequently masked by the application of nitrogen fertiliser. Mean yields increased by 80% due to the application nitrogen at the optimum rate compared to nil nitrogen. Most of the effects of set-aside treatment on grain yield were shown to be attributable to soil mineral nitrogen content, but at some sites, infections by take-all or eyespot also accounted for some of the variation. There were no effects of pests that could be related to treatment. The presence of sown clover during the set-aside period had the most consistent effect across sites, affecting tiller populations, grain yield and grain quality of cereal crops. At some sites, establishing a sown cover during the set-aside period, or cutting the cover more than once a year, improved grain yield and quality, and reduced the incidence of some specific weeds and disease.

Carbon cycle in the coastal zone: effects of global perturbations and change in the past three centuries

The coastal zone, consisting of the continental shelves to −200 m, including bays, lagoons, estuaries, and near-shore banks, is an environment that is strongly affected by two much bigger environmental reservoirs adjacent to it: the land and open ocean. In the coastal zone, as elsewhere in the Earth system, the biogeochemical cycle of carbon is coupled to, and driven by, the cycles of nitrogen and phosphorus through biological transfer processes. Human activities in the past 300 years have become an increasingly important geological factor with respect to the coastal zone through four major environmental perturbations: (1) C, N, and S emissions from fossil fuel burning; (2) changes in land-use activities resulting in gaseous C emissions, increased dissolved and particulate loads, organic matter transport, and feedbacks to biological production; (3) application of inorganic nitrogen- and phosphorus-containing fertilizers; and (4) discharges of sewage containing reactive organic C, N, and P. In addition, the mean global surface temperature of the planet has increased over this period of time by approximately 1°C, perhaps also because of human activities. Starting with the year 1700 as a base for the industrial-age perturbations on land, we analyzed the consequences of these five perturbations to the carbon cycle in the coastal zone using the thirteen-reservoir, process-driven model TOTEM for the coupled C–N–P–S biogeochemical cycles. An indicator of the reliability of the model is the good agreement of its results showing the time course of increasing atmospheric CO2 concentrations since the year 1700 with the observational results reported in the literature. During the past three centuries, there has been a significant increase in the amount of organic carbon transported from land and stored in coastal zone sediments. Of the total transported, about 65% was stored in sediments and the remaining 35% primarily recycled through exchange with the atmosphere and open ocean. The imbalance between the amounts of organic carbon produced by gross photosynthesis and remineralized has apparently increased slightly in favor of remineralization, corresponding to an increase in the degree of heterotrophy of the global coastal zone. This process, along with the release of CO2 from the formation of CaCO3, counteracts the invasion of CO2 from the atmosphere to coastal waters that is driven by the rise in atmospheric CO2 concentrations. An analysis of a possible reduction or full collapse of the oceanic thermohaline circulation, as believed to have occurred in the past and a possibility for future centuries, indicates that the CO2 transfer from the atmosphere to coastal waters would increase while that from the atmosphere to open ocean surface waters would decrease, if such an event took place. This is attributable to a reduced supply to the coastal zone of dissolved inorganic carbon by coastal upwelling from the deeper ocean, a process linked to the global conveyor belt of the thermohaline circulation. To date, fossil fuel CO2 emissions to the atmosphere, changes in land-use practices, and sewage discharges have been the three main factors affecting the carbon cycle in the global coastal zone. The latter inputs from land have apparently produced a slight increase in the heterotrophy of the global coastal zone. However, increases in the inputs of nutrient nitrogen and phosphorus from land to the coastal zone in the future may drive its trophic state toward net production and storage (autotrophy), thereby also increasing its potential role as a sink for atmospheric CO2. The direction of future change in net ecosystem production in the coastal zone strongly depends on changes in the relative magnitudes of organic carbon and nutrient N and P fluxes to the coastal zone via rivers, provided the upwelling fluxes remain constant.

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO3)2; +N and −N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined. Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO3 − and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H+ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO3 − but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO3 −, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO3 − is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO3 − had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner