Surface Soil Nitrogen Research Articles

Water-Soluble Organic Nitrogen in Surface Soil of a Tea Field under Heavy Application of Organic Matter

Water-Soluble Organic Nitrogen in Surface Soil of a Tea Field under Heavy Application of Organic Matter

Regional inventory of soil surface nitrogen balances in Indian agriculture (2000–2001)

Nitrogen regulates several ecological and biogeochemical processes and excess reactive nitrogen in the environment can lead to pollution problems, including the deterioration of air quality, disruption of forest processes, acidification of lakes and streams, and degradation of coastal waters. Much of the excess nitrogen inputs are related to food and energy production. An important step to understanding the sources of nitrogen and ultimately defining solutions to excess nitrogen is to describe the geographic distribution of agricultural nitrogen contributions from different regions. In this study, soil surface nitrogen loads were quantified for different states of India for the period 2000–2001. Nearly 35.4 Tg of nitrogen has been estimated as inputs from different sources, with output nitrogen from harvested crops of about 21.20 Tg. The soil surface nitrogen balance, estimated as inputs minus outputs, is found to be about 14.4 Tg surplus from the agricultural land of India. Livestock manure constituted a major percentage of total inputs (44.06%), followed by inorganic fertilizer (32.48%), atmospheric deposition (11.86%) and nitrogen fixation (11.58%). Nitrogen balance varied from deficit to surplus for different states. The highest nitrogen surplus was found in Uttar Pradesh (2.50 Tg) followed by Madhya Pradesh (1.83 Tg), Andhra Pradesh (1.79 Tg), etc. A negative nitrogen balance was found in Orissa (−0.01 Tg), Andaman Nicobar Islands (−0.32 Tg) and for some of the northeastern states. Major fertilizer consumption states were found to be Tamilnadu (204 kg/ha), Haryana (132 kg/ha), Punjab (148 kg/ha), followed by others. Similarly, nitrogen inputs from total livestock excretions were found to be high for Kerala (616 kg/ha), Jammu and Kashmir (389 kg/ha), Tamil Nadu (338 kg/ha), etc. The average nitrogen surplus of about 54 kg/ha observed for the agricultural land of the entire country of India is comparatively higher than the average surplus of about 31 kg/ha reported for European countries. These results, obtained from nutrient mass balance calculations, will be useful to formulate nutrient management plans relating to fertilizer usage, livestock management and for adopting some best management strategies at a state level in India.

Bermudagrass management in the Southern Piedmont U.S. IV. Soil surface nitrogen pools.

The fate of nitrogen (N) applied in forage-based agricultural systems is important for understanding the long-term production and environmental impacts of a particular management strategy. We evaluated the factorial combination of three types of N fertilization (inorganic, crimson clover [Trifolium incarnatum L.] cover crop plus inorganic, and chicken [Gallus gallus] broiler litter pressure and four types of harvest strategy (unharvested forage, low and high cattle [Bos Taurus] grazing pressure, and monthly haying in summer) on surface residue and soil N pools during the first 5 years of ‘Coastal’ bermudagrass (Cynodon dactylon [L.] Pers.) management. The type of N fertilization used resulted in small changes in soil N pools, except at a depth of 0 to 2 cm, where total soil N was sequestered at a rate 0.2 g ‧ kg‧ year1 greater with inorganic fertilization than with other fertilization strategies. We could account for more of the applied N under grazed systems (76–82%) than under ungrazed systems (35–71%). As a percentage of applied N, 32 and 48% were sequestered as total soil N at a depth of 0 to 6 cm when averaged across fertilization strategies under low and high grazing pressures, respectively, which was equivalent to 6.8 and 10.3 g ‧ m ‧ year. Sequestration rates of total soil N under the unharvested-forage and haying strategies were negligible. Most of the increase in total soil N was at a depth of 0 to 2 cm and was due to changes in the particulate organic N (PON) pool. The greater cycling of applied N into the soil organic N pool with grazed compared with ungrazed systems suggests an increase in the long-term fertility of soil.

Distribution of organic carbon and nitrogen in surface soils in the McMurdo Dry Valleys, Antarctica

The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding several lakes in the McMurdo Dry Valleys were measured in a relatively high-density sampling grid, in order to better understand the present-day distribution of organic matter in the ecosystem that is most readily transportable via aeolean processes. Carbon and nitrogen contents of the bulk sediments and size-differentiated sediments decreased in a series according to lake basins oriented along the Taylor Valley's main axis (Lake Fryxell > Hoare ≥ west lobe Bonney ≥ east lobe Bonney). Samples were also obtained around Lake Vida and showed this basin to contain less organic matter than those in the Taylor Valley. This regional spatial analysis supports the emerging view that each basin provides distinct environments for in situ microbial activity, lithogenic weathering, aeolian deposition and sorting that can be detected through synoptic sampling.

Agricultural nutrient balances as agri-environmental indicators: an OECD perspective

In its policy and indicators work on agriculture and the environment, the OECD has been addressing a large range of policy relevant issues of concern to countries, including the issue of nutrient use in agriculture. The policy issue in the case of agricultural nutrient use is to maintain sufficient nutrients to ensure the sustainable use of soil resources to improve crop and forage productivity, while reducing surplus nutrients from agriculture from causing water and air pollution. It is against this background that the paper describes the overall policy context of the nutrient use issue, in particular nitrogen use. The paper examines the use of the soil surface nitrogen balance indicator in the OECD work to analyse national trends in nitrogen use, and examines the data requirements, availability and coverage to complete nitrogen balance calculations. A brief overview of the current situation and recent trends in national nitrogen balance across OECD Member countries is provided. Finally, the paper discusses the interpretation of trends in national nitrogen balances, including consideration of benchmarks and targets, linkages with other agri-environmental issues, such as water quality, and also future challenges for quantitative work on nitrogen use issue in agriculture.

LOBLOLLY PINE PLANT COMMUNITY EFFECTS ON SOIL CARBON AND NITROGEN

Previous studies suggest that shifts in plant community structure may alter soil nutrient concentrations and availability. A study was conducted to determine the influence of species composition in loblolly pine (Pinus taeda L.) plant communities on surface soil nitrogen (N) and carbon (C) concentrations and potential mineralization after 7 years of growth and development. The study site is located in the Lower Coastal Plain physiographic region near Tallassee, AL. The soil is classified as a Cowarts loamy sand (Fine-loamy, siliceous, thermic Typic Kanhapludults). Utilizing herbicides, distinct plant communities were established in 1984 including herbaceous-hardwood-pine (HHwP), herbaceous-pine (HP), hardwood-pine (HwP) and pine only (P). Organic C and N and potential C and N mineralization were determined on surface soil samples (0 to 5-, 5 to 10-, and 10 to 20-cm depth increments) collected in February 1991. After 7 years, soil organic N differed among the plant communities; soil organic N was lower in the P than in communities including herbaceous species (HHwP and HP). These differences in soil organic N resulted from a net gain under HHwP and HP, rather than net loss under the P community. Gains in soil N may have been due to symbiotic N fixation. In laboratory incubations, respiration and N mineralization were lower in soil from the P than the HHwP and HP communities. Substrate quality as indicated by forest floor C/N and as manifested by relative N mineralization and C/N mineralized were also reduced in the P community compared with others. Our results suggest that silvicultural manipulation of loblolly pine communities may affect soil C and N and, in turn, could influence long-term site quality.

Soil Nitrogen Changes during Primary Succession on a Floodplain in Alaska, U.S.A.

Surface soil nitrogen changes along a subarctic vegetation chronosequence on a floodplain in central Alaska resulted from interactions between stochastic flooding and the influence of vegetation. River alluvium initially contributed 400 kg ha-1 of nitrogen to the top 200 mm of time-zero soils. Subsequent nitrogen accumulations were in part due to nitrogen fixers such as alder (Alnus tenuifolia). Kjeldahl nitrogen levels reached 1696 kg ha-~ in surface mineral soils of 30-yr-old alder stands. Extractable forms of nitrogen also increased four-fold in 30 yr. However, soil nitrogen increases also resulted from frequent floods that deposited additional nitrogen-rich alluvium. Frequently flooded low terraces had high silt content and relatively high nitrogen levels. Frequent flooding of some forested upper terraces resulted in poorer development of forest floors, higher sand content, and dilution of nitrogen levels compared with upper terraces that were less often flooded. Although nitrogen levels were primarily determined by biotic factors, periodic flooding and associated changes in particle size also affected concentration and pool sizes of nitrogen in soils of the vegetation chronosequence.

Disturbance, Nitrogen Availability, and Nitrogen Losses in an Intensively Managed Loblolly Pine Plantation

The interactive effects of harvest intensity, site preparation, and herbicide treatment were evaluated in a clear—cut Piedmont site in North Carolina. Forest harvesting caused increased nitrogen mineralization and nitrification in all treatments, but harvesting without additional treatment had little effect on nitrate—nitrogen pool sizes and losses. The removal of most surface organic material during intensive site preparation led to greatly increased nitrate pool sizes and losses. Treatment with herbicide accentuated this effect, and in combination such removals and herbicide applications led to accumulations of nitrate—nitrogen in surface soil of 27 and 24 kg/ha in the first and second summers following site preparation. Nitrogen losses by leaching, denitrification, and erosion were also greatest in the plots where organic residues had been removed and herbicides applied. These results suggest that microbial immobilization controlled nitrogen pool sizes and losses, and this suggestion was confirmed using 15N. Soils from the plots without residue removal or herbicide treatment immobilized >90% of added 15N in 28 d, while those from the residue removal/herbicide treated plots immobilized <70%. Microbial activity was the predominant process regulating nitrogen availability and losses following disturbance in this site; site—preparation practices that removed important substrates for microbial metabolism caused elevated nitrogen losses.

FIXED AMMONIUM IN NIGERIAN SOILS I. SELECTION OF A METHOD AND AMOUNTS OF NATIVE FIXED AMMONIUM

SummaryThree of the common methods for the determination of native fixed ammonium in soils‐the Rodrigues modified, the Bremner KOH method, and the Silva Bremner method‐were evaluated and the Silva‐Bremner method was chosen. Native fixed ammonium in 212 profile samples representing different soil types and sampling localities in Nigeria was found to range from 4 to 98 ppm. Fixed ammonium accounted for 1‐7 per cent of total nitrogen in surface soils and 3‐48 per cent in the sub‐soils. More than half of the values fell within the ranges 2‐4 and 8‐20 per cent respectively. The results do not agree with the high values reported earlier for four Nigerian soil profiles.Fixed ammonium, both in absolute amounts and as a percentage of total nitrogen, increased with depth in most profiles though maximum amounts were not necessarily attained in the lowest horizons. Fixed ammonium values were lower in soils derived from sandy parent material than in those derived fromigneous or metamorphic rock and were generally less in the more humid southern parts of the country than in the drier north. Fixed ammonium, especially in subsoils, contributes to the nitrogen economy in these soils.

Release of ammonium and organic matter from soil by hydrofluoric acid and effect of hydrofluoric acid treatment on extraction of soil organic matter by neutral and alkaline reagents

1. The effect of treating mineral soils with hydrofluoric acid to decompose clay minerals on the extraction of soil organic matter by alkaline and neutral reagents has been investigated.2. It was found that treatment of soil with hydrofluoric acid had little effect on the extraction of organic matter by alkaline or neutral reagents, but that it released considerable amounts of ammonium and organic matter. More than 90% of the nitrogen in Rothamsted soils was dissolved by repeated treatments with dilute solutions of hydrofluoric acid and sodium hydroxide.3. It is shown that treatment of clay minerals with n-HF:n-HCl solution at room temperature for 24 hr. effects quantitative release of fixed ammonium from clay minerals and that similar treatment of soil is not likely to cause significant decomposition of organic nitrogen compounds to ammonium. It is suggested that a method based on this treatment may prove useful for the determination of fixed ammonium in soil. Results obtained by this method indicated that 4–8% of the nitrogen in surface soils and 19–45% of the nitrogen in subsoils examined was in the form of fixed ammonium.4. It is concluded that some mineral soils contain a significant quantity of ammonium and organic matter intimately associated with clay minerals and that this clay-bound material is not dissolved by neutral and alkaline reagents used for the extraction of soil organic matter, but is released by hydrofluoric acid.