Mineralization of biuret nitrogen in soil

Summary Study of the mineralization of biuret N under aerobic and anaerobic conditions in a sandy loam showed that higher amounts of mineral N accumulated under anaerobic incubation than under aerobic conditions. Under waterlogged incubation, 46.8% of the 100 ppm biuret N was mineralized while under aerobic conditions only 18.3% of biuret-N was converted into mineral N during 5 weeks at 30°C. The results of the study bring out slow-release nature of biuret-N.     

Nitrogen supplying ability of some Philippine rice soils

Summary The nitrogen-supplying power of eight Philippine rice soils was measured by consecutively growing six crops of IR 32 rice under flooded conditions in a greenhouse pot experiment. The dry matter yields or nitrogen uptake of rice were found to be highly positively correlated with the organic carbon and the total nitrogen contents of the soils, as well as with the amounts of ammonium released during an anaerobic incubation test at 30°C for 2 weeks.The results of the study bring out the usefulness of simple tests like organic carbon content and total nitrogen content of soils for predicting the nitrogen-supplying power to lowland rice.     

Nitrogen mineralization dynamics in grass monocultures

Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9–14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1–day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (N_o) were estimated, the best model treated N_o as two pools: a labile pool, which differed among species in size (N_l, range 2–3% of total N) and rate constant (h, range 0.04–0.26 wk^–1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.     

Nitrogen mineralization,nitrification and denitrification in upland and wetland ecosystems

Summary Nitrogen mineralization, nitrification, denitrification, and microbial biomass were evaluated in four representative ecosystems in east-central Minnesota. The study ecosystems included: old field, swamp forest, savanna, and upland pin oak forest. Due to a high regional water table and permeable soils, the upland and wetland ecosystems were separated by relatively short distances (2 to 5 m). Two randomly selected sites within each ecosystem were sampled for an entire growing season. Soil samples were collected at 5-week intervals to determine rates of N cycling processes and changes in microbial biomass. Mean daily N mineralization rates during five-week in situ soil incubations were significantly different among sampling dates and ecosystems. The highest annual rates were measured in the upland pin oak ecosystem (8.6 g N m^–2 yr^–1), and the lowest rates in the swamp forest (1.5 g N m^–2 yr^–1); nitrification followed an identical pattern. Denitrification was relatively high in the swamp forest during early spring (8040 g N₂O–N m^–2 d^–1) and late autumn (2525 g N₂O–N m^–2 d^–1); nitrification occurred at rates sufficient to sustain these losses. In the well-drained uplands, rates of denitrification were generally lower and equivalent to rates of atmospheric N inputs. Microbial C and N were consistently higher in the swamp forest than in the other ecosystems; both were positively correlated with average daily rates of N mineralization. In the subtle landscape of east-central Minnesota, rates of N cycling can differ by an order of magnitude across relatively short distances.     

黄土高原典型土壤有机氮矿化过程

以黄土高原从北向南不同地区典型土壤类为对象,采用Bremner淹水培养法,研究黄土高原典型土壤有机氮的矿化过程。结果表明,淹水培养期间矿化出的部分NH4^＋-N会被粘土矿物固定,固定量因土壤不同而异,因此在测定有机氮矿化量时,只有考虑这一部分氮素,才可获得可靠结果。不同土壤有机氮量矿化明显不同,表现为土垫旱耕人为土〉黄土正常新成土〉简育干润均腐土〉干润砂质新成土,从南到北氮素矿化量呈减小趋势。添加C／N低（C／N比为21．7）的紫花苜蓿（Medicago stativa）茎叶有利于促进土壤有机氮矿化,而添加C／N高（C／N比为43．3）的长芒草（Stipa bungeana）会促进矿质氮的生物固定;不同类型植被土壤间在培养20、40d和60d时的矿化量差异显著（P值分别为0．0177、0．0109和0．0073）,均表现为均为林地土壤〉裸地土壤〉草地土壤〉农田土壤;从平均看,加（NH4）2SO4后有机氮矿化量有一定减少。在不同培养阶段,不同土类间氮素矿化率不同,在20d和40d时存在显著差异（P分别为0．0092和0．0381）,60d时差异不显著,不同土类氮素矿化率的大小顺序为于润砂质新成土〉黄土正常新成土〉土垫旱耕人为土〉简育干润均腐土,这一结果说明在淹水条件下,黄土高原土壤从南到北易矿化氮所占全氮比例呈增加趋势。     

Incubation experiments on nitrogen mineralization in loess and sandy soils

Summary In aerobic incubation experiments, nitrogen mineralization was investigated in agricultural loess and sandy soils. Fresh, fieldmoist samples were used for incubation. Using an optimization procedure the N-mineralization was split into two nitrogen fractions: A resistant, slowly decomposable organic N-fraction (index rpm) and a fast decomposable N-fraction (index dpm).Loess- and sandy soils showed similar mean reaction coefficients for N-mineralization. The results also indicated that the amount of mineralizable nitrogen in the resistant N-fraction depended directly on clay content.Soil sampling at different times during crop growing period gave different mineralization amounts and courses.Effect of added plant residues on N-mineralization, was also studied by incubation. Variation of type and quantity of added residues changed the net N-mineralization in a characteristic way: Sugar beet leaves, added in minced form, caused an increase in mineralization; while straw caused a temporary immobilization, followed by remineralization.Incubation experiments on undisturbed soil columns showed nearly linear mineralization with time.This paper was presented in part at the 1983 Congress of the German Soil Science Society held at Trier.     

Nitrification in some tropical soils

Summary Nitrification of soil N in 8 mineral and 2 histosols having a wide range in pH (3.4 to 8.6), organic C (1.22 to 22.70%) and total N (0.09 to 1.20%) was studied by measuring nitrate fromation under aerobic incubation of the soil samples at 30°C for 4 weeks. The amounts of NO₃-N produced in the soils varied from 0 to 123 μg/g of soil. Soil N in the two acid sulfate soils and one other acid soil did not nitrify under conditions that stimulate nitrification. Soils having pH more than 6.0 nitrified at a rapid rate and released NO₃-N ranging from 98 to 123 μg/g. The two organic soils differed considerably in their capacity to nitrify though the total amounts of mineral N released were similar in these soils. The amounts of NO₃-N formed in the soils was highly positively correlated with the soil pH but was not significantly correlated with the organic C of total N content of the soils. Statistical analysis also showed that nitrate formation was not significantly correlated with soil pH in soils having pH higher than 6.0.     

Patern of nitrogen release during decomposition of some green manures in a tropical alluvial soil

Summary The pattern of release of ammonium and nitrate nitrogen during decomposition of glyricidia, sunflower, centrosema, calapagonium and crotolaria under aerobic and anaerobic conditions, in an alluvial soil over a period of 7 weeks was studied. Under aerobic conditions, the NH₄ ⁺–N production reached the maximum after the 4th week. Nitrate-N and total available-N increased in all cases throughout the incubation period except in sunflower. This showed a nitrification inhibitory effect and had a relatively high C/N ratio (11.0) and low total N content (2.8%). In general the increase in NH₄ ⁺–N and NO₃ ^––N was more rapid in the early stages of incubation.Under anaerobic conditions, the production of these nutrients was considerably low. Soil organic matter mineralized faster than the added organic material which started to decompose slowly after sometime. Nitrate-N tend to decrease during incubation attributable to denitrification.     

Nitrogen mineralization and its controlling factors in various kinds of temperate humid-zone soils

The N mineralization capacity of 41 temperate humid-zone soils of NW Spain was measured by aerobic incubation for 15 days at 28°C and 75% of field capacity. The main soil factors affecting organic N dynamics were identified by principal components analysis. Ammonification predominated over nitrification in almost all soils. The mean net N mineralization rate was 1.63% of the organic N content, and varied according to soil parent materials as follows: soils on basic and ultrabasic rocks < soils over acid metamorphic rocks < soils developed over sediments < soils over acid igneous rocks < soils on limestone. The N mineralization capacity was lower in natural soils than in cropped soils or pastures. The accumulation of organic matter (C and N) seems to be due to poor mineralization which was caused, in decreasing order of importance, by high exchangeable H-ion levels, high Al and Fe gel contents and, to a lesser extent (though more markedly in cropped soils), by silty clay texture and exchangeable Al ions.     

Seasonal variation in nitrogen uptake and turnover in two high-elevation soils: mineralization responses are site-dependent

In arctic and alpine ecosystems, soil nitrogen (N) dynamics can differ markedly between winter and summer months, and nitrogen losses can be measurable during the spring and fall transitions. To explore the effect of seasonality on biogeochemical processes in a temperate alpine environment, we used a combination of field incubations (year-round) and ¹⁵N tracer additions (late fall, early spring, summer) to characterize soil N dynamics in a wet and dry meadow in the Sierra Nevada, California. The snowmelt to early summer season marked a period of high ¹⁵N uptake and turnover in the two soils, coincident with the increase in microbial N pools at the start of snowmelt (wet and dry meadow); an increase in net N mineralization and net nitrification as snowmelt progressed (wet meadow only); and measureable net production of ¹⁵N-NH₄ ⁺ in mid-summer (wet and dry meadow). Whereas fluctuations in microbial biomass were generally synchronous between the wet and dry meadow soils, only wet meadow soils appeared to mineralize N in response to declines in the microbial N pool. Net N mineralization and net nitrification rates in the dry meadow soil were negligible on all but one sampling date, in spite of periodic decreases in biomass of up to 60%. Across both sites, high ¹⁵N recoveries in microbial biomass N, rapid ¹⁵N-NH₄ ⁺ turnover, and low or negative net ¹⁵N-NH₄ ⁺ fluxes suggested tight cycling of N, particularly in the late fall and early spring.     

Assay of nitrogen supplying capacity of tropical rice soils

Summary The nitrogen supplying capacity of 39 wetland rice soils evaluated by two anaerobic incubation methods and six chemical methods was compared with N uptake of IR 26 rice grown on these soils under flooded conditions in a greenhouse pot study. The uptake of N by rice correlated highly with the N supplying capacity determined by anaerobic incubation methods involving incubation of soils at 30°C for 2 weeks (r=0.84^**) or at 40°C for 1 week (r=0.82^**) as well as with the organic carbon (r=0.82^**) and total N (r=0.84^**) contents of soils. Among the chemical indexes, available N determined by the oxidative release of soil N by alkaline permanganate, acid permanganate, acid dichromate and hydrogen peroxide also provided good index of soil N availability to rice. According to these results soil organic carbon and total N contents seem to be good indexes of available nitrogen in tropical wetland rice soils.     

Prediction of nitrogen availability and rice yield in lowland soils: Nitrogen mineralization parameters

Field experiments were conducted under flooded soil conditions using Maahas clay amended with urea and rice straw-sesbania mixtures during the wet and dry seasons. Parallel laboratory incubation tests were done. The objectives were 1) to determine N mineralization patterns and establish the relationship between mineralization parameters and either N availability or grain yield, and 2) to correlate the results of organic N mineralization studies in the laboratory with data from field experiments. The N mineralization patterns of flooded soils in the laboratory followed a logistic function. In laboratory studies, mineralization potential was positively correlated with extractable soil NH₄ ⁺-N at the end of the incubation period (cumulative available N). Likewise, mineralization potential calculated from laboratory studies was positively correlated with N uptake and grain yield from field studies. Extractable (NH₄ ⁺+NO₃ ^–)-N in the field correlated positively with extractable NH₄ ⁺-N in the laboratory. The extractable NH₄ ⁺-N from laboratory incubations at 14 days after transplanting, panicle initiation, and maturity was also highly and positively correlated with grain yield from field experiments.     

Nitrogen mineralization and potential nitrification at different depths in acid forest soils

Yield decline of cereals grown in monoculture may be alleviated with alternative crop management strategies. Crop rotation and optimized tillage and fertilizer management can contribute to more sustainable food and fiber production in the long-term by increasing diversity, maintaining soil organic matter (SOM), and reducing adverse effects of excessive N application on water quality. We investigated the effects of crop sequence, tillage, and N fertilization on long-term grain production on an alluvial, silty clay loam soil in southcentral Texas. Crop sequences consisted of monoculture sorghum (Sorghum bicolor (L.) Moench,) wheat (Triticum aestivum L.), and soybean (Glycine max (L.) Merr), wheat/soybean double-crop, and rotation of sorghum with wheat/soybean. Grain yields tended to be lower with no tillage (NT) than with conventional tillage (CT) early in the study and became more similar after 11 years. Nitrogen fertilizer required to produce 95% to maximum sorghum yield was similar for monoculture and rotation upon initiation of the experiment and averaged 16 and 11 mg N g^-1 grain with NT and CT, respectively. After 11 years, however, the N fertilizer requirement became similar for both tillage regimes, but was greater in monoculture (17 mg N g^-1 grain) than in rotation (12 mg N g^-1 grain). Crop sequences with double-cropping resulted in greater land use efficiency because similar or lower amounts of N fertilizer were required to produce equivalent grain than with less intensive monoculture systems. These more intensive crop sequences produced more stover with higher N quality primarily due to the inclusion of soybean in the rotation. Large quantities of stover that remained on the soil surface with NT led to greater SOM content, which increased the internal cycling of nutrients in this soil. In southcentral Texas, where rainfall averages nearly 1000 mm yr^-1, more intensive cropping of sorghum, wheat, and soybean with moderate N fertilization using reduced tillage can increase grain production and potentially decrease N losses to the environment by cycling more N into the crop-SOM system.     

Nitrogen mineralisation in soils of varying texture,moisture and organic matter

Summary Estimates of nitrogen availability based on the nitrogen mineralisation potential,N ₀, and the mineralisation rate constant,k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July.There was a significant relationship between values calculated fromN ₀ andk and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising.The time required for mineralisation of 50% ofN ₀ indicated that less than half the potential value would become available in a normal temperature growing season.     

Nitrogen mineralization in a green manure-amended soil as influenced by cropping history and subsequent crop

A greenhouse experiment was conducted to determine the influence of cropping variables on nitrogen dynamics in a soil amended with green manure. Surface soil from various long-term spring wheat rotations was amended with¹⁵N-labelled legume green manure (Lathyrus tingitanus) and subsequently cropped (canola [Brassica napus] and spring wheat [Triticum aestivum]) or incubated without a crop for 56 days in a greenhouse. Nitrogen mineralization from both the indigenous soil N and from green manure was suppressed in cropped soil. Net N mineralization in the uncropped and cropped treatments averaged 73 and 43 mg kg⁻¹, respectively. This difference was attributed, in part, to enhanced biological immobilization in the rhizosphere. Previous cropping practices also had significant effect on N mineralization, largely by their influence on indigenous organic matter quality. These observations suggest that short-term N mineralization is favored by fallowing soil after green manure application whereas N retention in organic matter is favored by immediate cropping. Contribution 3878873     

Differential effects of lichens,mosses and grasses on respiration and nitrogen mineralization in soils of the New Jersey Pinelands

In the New Jersey Pinelands, severely disturbed areas often do not undergo a rapid succession to forest; rather, a patchy cover of lichens, mosses and grasses persists for decades. We hypothesized that these plant covers affect soil microbial processes in different ways, and that these effects may alter the successional dynamics of the patches. We predicted that the moss and grass covers stimulate soil microbial activity, whereas lichens inhibit it, which may in turn inhibit succession. We collected soil cores from beneath each type of cover plus bare soil within two types of highly disturbed areas—sites subjected to hot wildfires, and areas mined for sand. Organic matter (OM) content, soil respiration and potential N mineralization were measured in the cores. Soils under mosses were similar to those under grasses; they accumulated more OM and produced more mineral N, predominantly in the form of ammonium, than either the bare soils or the soils beneath lichens. Mineralization under lichens, like that of the bare soils but unlike the soils beneath mosses or grasses, was dominated by net nitrification. These patterns were reproduced in experimentally transplanted moss and lichen mats. Mosses appear to create high-nutrient microsites via high rates of OM accumulation and production of ammonium, whereas lichens maintain low-nutrient patches similar to bare soil via low OM accumulation rates and production of mineral N predominantly in the mobile nitrate form. These differences in soil properties may explain the lack of vascular plant invasion in lichen mats, in contrast to the moss-dominated areas.     

N deposition, N transformation and N leaching in acid forest soils

Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha^–1 year^–1 (D20, B150, S45) and 15–21 kg ha^–1 yr^–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha^–1 (D40, D60, S90), and 36–43 kg ha^–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha^–1 yr^–1 (B150, S45, D60) and 28–66 kg ha^–1 yr^–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha^–1 yr^–1 (S45, D40, S90) and between 176–209 kg ha^–1 yr^–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha^–1 yr^–1 at S45, 36 kg ha^–1 yr^–1 at S90 and between 69 and 91 kg ha^–1 yr^–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.     

Inhibitory effects of commercial potassium chloride on the nitrification rates of added ammonium sulphate in an acid red yellow podzolic soil

Summary Rates of nitrification of ammonium sulphate in an acid red yellow podzolic tea soil in Sri Lanka with and without the addition of commercial potassium choride (95% KCl) and analytical grade KCl was studied under field conditions and in a laboratory incubation experiment. Addition of KCl effectively suppressed nitrification and this suppression was found to be due to the presence of Cl-ions rather than K-ions.     

Net mineralization and nitrification rates in a clay soil measured and predicted in permanent grassland from soil temperature and moisture content

Summary Net mineralization of N and net nitrification in field-moist clay soils (Evesham-Kingston series) from arable and grassland sites were measured in laboratory incubation experiments at 4, 10 and 20°C. Three depth fractions to 30 cm were used. Nitrate accumulated at all temperatures except when the soil was very dry (=0.13 cm³ cm^–3). Exchangeable NH₄-ions declined during the first 24 h and thereafter remained low. Net mineralization and net nitrification approximated to zero-order reactions after 24 h, with Q₁₀ values generally <1.6. The effect of temperature on both processes was linear although some results conformed to an Arrhenius-type relationship. The dependence of net mineralization and net nitrification in the field soil on soil temperature (10 cm depth) and moisture (0–15, 15–25, 25–35 cm depths) was modelled using the laboratory incubation data. An annual net mineralization of 350 kg N ha^–1 and net nitrification of 346 kg N ha^–1 were predicted between September 1980 and August 1981. The model probably overstressed the effect of soil moisture relative to soil temperature.     

Nitrogen uptake in barley after spring incorporation of 15N-labelled Italian ryegrass into sandy soils

A 5-month laboratory incubation experiment was conducted to study the immobilization-mineralization of N in soil to which dried or composted ¹⁵N labelled ryegrass (Lolium italicum L.) had been added. Cellulose was added to dried ryegrass to give a C/N ratio similar to that of composted ryegrass. Exchangeable NH₄ ⁺ and NO₃ ^–, HCl-hydrolyzable N forms, microbial biomass N, NaOH-soluble and insoluble N were monitored during incubation. Dried ryegrass brought about a significant increase in total and labelled exchangeable NH₄ ⁺, while a rapid immobilization and a subsequent slow release of exchangeable NH₄ ⁺ was observed in soil with composted ryegrass, together with a resistance to degradation of the labelled humic substances. Compounds synthesized during the composting process and resistant to microbial decomposition probably caused an increase in the amino-acid fraction of soil. These findings suggest that composting can reduce the risk of N losses.