Nitrogen Availability Indices Research Articles

Evaluation of Nitrogen Availability Indexes for a Sludge Compost Amended Soil

AbstractSeveral N availability methods were evaluated on a sludge amended soil, since sludge applications are usually based on N availability and a soil N evaluation to optimize loading rates. Yearly amendments of composted, lime‐stabilized, raw sludge were applied, at 0, 56, 112, and 224 Mg ha−1, to an Elkton silt loam soil (Typic Ochraquults), in Beltsville, MD, as follows: whole plots (1975–1977), half plots (1978), and no plots (1979–1981). In 1978 and 1981, surface and subsurface soil samples were collected and maize (Zea mays L.) total N uptake was determined. The biological method (73‐week aerobic incubation [NT]) of assessing soil N availability revealed an initial rapid miner. alization phase (NE) over the first 28 weeks and a constant phase thereafter. The chemical methods were total soil N (TN), acid KMnO4 oxidizable N (P), autoclave extractable N (A), and 2 M KCl extractable NH+4‐N (K). Curvilinear regression analyses relaling maize N uptake to these N indexes gave the following R2 values: NE, 0.93; NT, 0.94; TN, 0.93; P, 0.92; A, 0.95; and K, 0.92. All methods were equally sensitive on sludge treated soils; however, the incubation procedure was best on untreated soil. Including second zone soil N and expressing the results on a root‐zone volume basis improved N uptake predictions with unfertilized controls, but was unnecessary for sludge treated plots. These results indicate that chemical N availability indexes can be used to assess soil N availability on sludge treated land; provided they are calibrated to local soil‐crop‐climate conditions.

Evaluation of alkaline permanganate method and its modification as an index of soil nitrogen availability

To find out a rapid and reliable procedure for estimating soil available nitrogen (N), the standard alkaline-permanganate extraction and its modification to include soil NO3 were evaluated. The N values obtained with the standard method showed a poor correlation with the mineral N of incubation test and plant uptake (r=0.36 and 0.37 respectivelyP<0.05 in both the cases) whereas the results obtained with the modified method gave highly significant correlations (r=0.84 and 0.76 respectively.P<0.01 in both the cases). The data supplied further verification of the modified alkaline-permanganate method for assessing N availability in soils.

Modification of the acid permanganate method for obtaining an index of soil nitrogen availability

The acid permanganate method proposed as a chemical index of soil nitrogen (N) availability simply measures the mineralizable N. A modification of the method has been proposed that allows the estimation of soil mineral N simultaneously. The N values obtained by the modified method correlated highly significantly with the mineral N of incubation test (r=0.80,P<0.01) and plant uptake (r=0.69,P<0.01).

A comparison of several nitrogen- availability indices on four Natal maize-producing soils

Four methods used in obtaining nitrogen-availability indices were compared using soil and plant samples taken from maize trials conducted on four widely differing Natal soils. NO3 − N was determined after extraction of the soil with NH4HCO3, Ca(OH)2 and KCl, using a specific ion electrode, phenoldisulphonic acid and brucine respectively. In addition, NO3 -N and NH4 + -N were determined after steam distillation of KCl extracts. The measurements so obtained were correlated with the rates of nitrogen application and leaf-N content at flowering. The four NO3 − -N determinations were all closely correlated with each other and with the level of N applied. The overall correlation across soils between N applied and increase in NO3 − -N exceeded 0,85. Inclusion of NH4 + - N did not materially improve the relationship between soil test and N application rate. NO3 − -N was also well correlated with leaf-N content. The levels of NO3 − -N measured in the absence of fertilizer N relate well to previously measured N res...

Effects of Clearfelling and Site Preparation on Nitrogen Mineralization in a Southern Pine Stand

AbstractA clearcut forest site (45‐year‐old natural stand of Pinus elliottii Engelm. and Pinus palustris Mill.) was subjected to different intensities of site preparation to determine management impacts on N availability. Using a laboratory aerobic soil incubation technique, N mineralization potentials (N mineralizable over time) (No) were determined to be 25.0, 23.3, and 17.7 µg/g for soils from an uncut control area; a burned and chopped area; and a bladed, disced, and bedded area, respectively. The No of soil from the intensively treated area was significantly lower than the others when measured in the laboratory; however, simulations of field conditions indicated that more N may be mineralized in soils from intensively treated sites due to more favorable soil moisture and temperature conditions. Mineralization rates for these three areas, however, were not significantly different, and C/N ratios (28 and 26 for the chopped and bladed sites, respectively) for the clearcut and prepared areas did not suggest a difference in N availability. Ratios of organic matter/soluble carbon (OM/Ca) increased from 79 to 136 with treatment intensity and suggest that the N associated with the organic matter remaining on the most intensively treated site may be more resistant to decomposition. Nitrogen availability is a function of substrate quality and microenvironmental conditions. Harvesting and site treatment affected both of these. Laboratory determinations of No appear to be a better index of nitrogen availability than C/N, Cs, or total N, but do not adequately account for differences in mineralization due to treatment‐induced changes in the soil environment.

Evaluation of acid permanganate extraction as an index of soil nitrogen availability

A chemical measure of soil nitrogen (N) availability has been evaluated. The method involved the estimation of initial mineral N, plus mineralizable N released with 0.05N KMnO4 in 1NH2SO4. The results obtained correlated highly significantly with the N uptake by wheat plants (r=0.72,P<0.01).

Evaluation of Nitrogen Availability Indices for Rice in Alluvial Soils

Evaluation of Nitrogen Availability Indices for Rice in Alluvial Soils

Correlations between indexes of soil nitrogen availability and nitrogen percent in plant, nitrogen uptake, and dry-matter yield of rice grown in the greenhouse

Relationships between available nitrogen determined by two anaerobic incubation methods (30°C for 2 weeks: 40°C for 1 week) and seven chemical indexes (Organic C, total N, ammonium released by acid dichromate, acid permanganate, alkaline permanganate, hydrogen peroxide and dilute sulfuric acid) and nitrogen percent in rice plant, nitrogen uptake and dry-matter yield of IR 26 rice grown under submerged conditions in pots were investigated using 39 Philippine wetland rice soils differing markedly in their capacities to supply nitrogen. It was found that all the availability indexes were best correlated with nitrogen uptake of rice followed by N% in rice plants at 55 days after seeding. Dry-matter yield of rice was also significantly correlated with the available nitrogen status but the correlation coefficients were the lowest. It is concluded that for unfertilized soils, nitrogen uptake provides a better criterion for evaluating the performance of nitrogen availability indexes for wetland rice.

Effect of temperature and time of storage of dry soil samples on a chemical index of N availability

The effect was studied of storage temperature on the index of available soil N wich uses U.V. absorbance of a 0.01M NaHCO3 extract as an indicator. The U.V. absorbance was found to increase at a non-linear rate for four soils stored at temperatures of 50, 75, and 150°C. The change in extract absorbance due to extended soil storage at each of these temperatures was positively correlated to the percent organic matter, percent N, C/N value and concentration of humic substances in soils, but not to the extract absorbance prior to soil storage. These findings were not consistent with room temperature storage data which showed a linear increase in extract absorbance with soil storage time. The change in absorbance for the room temperature case was not related to any of the soil parameters mentioned above. Analysis of a soil stored at 105°C showed an increase in ninhydrin-detectable N, protein N and Kjeldahl N of the NaHCO3 extract, while the apparent molecular weight distribution of extracted organic matter (as determined by gel filtration) showed only a slight change. As a comparison to the NaHCO3 extract, a boiling CaCl2 extract of the same soil was also analyzed; and the absorbance at 260 nm was found to increase in a curvilinear fashion with starage time at 75°C but to less of an extent than was noted with the NaHCO3 extract. Nitrogen availability indexes based on the U.V. absorbance of these extracts, particularly those utilizing the NaHCO3 extract, would be significantly affected by soil storage at elevated temperatures.

Mineralizable Soil Nitrogen as an Index of Nitrogen Availability to Forest Trees

AbstractSoil N mineralized during 14‐day anaerobic incubation at 30°C is evaluated as an index of forest soil fertility and site productivity. Mineralizable soil N determined under standard conditions correlates significantly with N mineralized anaerobically for 6 months in the field, with site index and yield potential of Pinus ponderosa L. growing on volcanic, metavolcanic, and metasedimentary soils, and with foliar concentrations of N. Soils testing less than 12 ppm of mineralizable N are judged clearly deficient, but stands of pine and fir on soils testing as high as 16 ppm of N still may respond well to fertilization. Absolute variability in mineralizable soil N decreases with soil depth and increases with the magnitude of the soil test mean, but relative variability is constant. Comparing ammonium produced during laboratory incubation with that mineralized over 6 months in the field shows that field soil temperature has a strong bearing on the interpretation of the laboratory test.

A laboratory method for assessment of nitrogen availability in soils

The nitrogen availability index determined as nitric acid potential gave significant correlations with the yield of bajra, wheat and rice crops in experiments conducted on alluvial soils of Delhi at the IARI Farm. The coefficient of correlation was also the highest when data from similar experiments on wheat on alluvial, grey brown, sierozem and medium black soils from different places in India were pooled. It was found that the nitric acid potential seems to be independent of soil type and is also applicable to various agroclimatic conditions.

Field Testing of Several Nitrogen Availability Indexes

AbstractWith no quick, reliable soil N availability test for humid region soils, N fertilizer recommendations in these areas are being made on the basis of crop N requirements. When the variability in N‐supplying capability of soils is not taken into account, most N fertilizer recommendations will be inaccurate, leading to inefficient use of N, less economical crop production, and the potential for N pollution of the nation's air and water. Although several N availability indexes have proved to be well correlated with the N‐supplying capability of a soil in greenhouse or laboratory experiments, very little testing of these indexes has been done with field experiments. Eight N availability indexes were correlated with the capability of eight Pennsylvania soils to supply N to field‐grown corn (Zea mays L.) in 1976 and 1977. Boiling 0.01M CaCl2 and 0.01M NaHCO3‐extractable N were both significantly correlated at the 1% level (r = 0.86 and 0.77, respectively) with the N‐supplying capability of the soils from the combined 1976 and 1977 experiments. Autoclave‐extractable NH4‐N and total soil N were significantly correlated with the soil supplying capability at the 5% confidence level (r = 0.70 and 0.68, respectively). Walkley‐Black soil organic matter, soil NO3‐, and H2SO4‐extractable and KCl‐extractable N were not significantly correlated with N availability in the field. Though four of the indexes were well correlated with the N availability in the soil, time and expense necessary for these analyses may preclude their being used routinely by soil testing laboratories.

Prediction of Nitrogen Fertilizer Requirements of Field Crops. II. Application of Theoretical Models to Malting Barley1

AbstractFive indices of soil organic nitrogen availability and mineral plus fertilizer nitrogen were used in the prediction of grain yield, grain protein content, and grain protein nitrogen of Moravian barley. Three mathematical models were employed, one of which included only soil mineral plus fertilizer N for prediction of crop parameters. The remianing two models, which included both organic and mineral plus fertilizer N showed improved predictability of crop parameters. No organic nitrogen measure showed superiority to others, however, one equation model was advantageous in studying the relative contribution of soil organic N to crop production.

Determination and Isotope‐Ratio Analysis of Different Forms of Nitrogen in Soils: 6. Mineralizable Nitrogen

AbstractAn incubation method of estimating mineralizable soil nitrogen which does not require preliminary analyses to determine the amount of water required for incubation and is applicable without modification to soils having widely different textures is described. It is based on the finding that the amount of water required for maximal aerobic mineralization of nitrogen during incubation of soils is practically the same for different soils (ca. 0.6 ml/g of soil) if the soil sample is mixed with three times its weight of 30‐ to 60‐mesh quartz sand before incubation. The method involves determination of the (exchangeable ammonium + nitrate + nitrite)‐N produced when 10 g of soil mixed with 30 g of sand are treated with 6 ml of water and incubated at 30C for 14 days under conditions which ensure adequate aeration without loss of water. It is simple and precise, and evaluation tests indicate that it provides a good index of soil nitrogen availability.

Comparison and Evaluation of Laboratory Methods of Obtaining an Index of Soil Nitrogen Availability1

AbstractAn evaluation of incubation and chemical methods of obtaining an index of soil N availability showed that incubation procedures involving estimation of the total mineral N produced on incubation of soil under aerobic conditions at 30C for 14 days or estimation of the ammonium N produced on incubation of soil under waterlogged conditions at 40C for 7 days provided a good index of the availability of the N in Iowa soils to ryegrass. It also showed that the results obtained with these soils by a chemical procedure involving estimation of the N extracted by boiling water and potassium sulfate solution were closely related to N uptake by ryegrass and indicated that this procedure deserves consideration as a routine method of obtaining an index of soil N availability. Air‐drying and air‐dry storage of soil samples had marked effects on the results obtained by the incubation methods studied, but had little effect on the results obtained by the chemical methods found to provide a good index of soil N availability.

A Chemical Index of Soil Nitrogen Availability

MANY laboratory methods of obtaining an index of the availability of soil nitrogen to plants have been proposed, but biological procedures involving estimation of the amount of nitrogen mineralized when soil is incubated under aerobic conditions at 28°-35° C for 1–4 weeks have been generally preferred1. However, recent work has shown that the results of these incubation procedures are greatly affected by the method and duration of storage of the soil sample before analysis. This has led to a renewal of interest in chemical methods, because it seems likely that the results of chemical methods will be less affected by preliminary handling and storage of the soil sample than the results of incubation methods. A chemical approach to the problem of obtaining an index of soil nitrogen availability is also encouraged by the experience that chemical methods of analysis are usually simpler and more rapid and precise than biological techniques. Studies in our laboratory of chemical methods of obtaining an index of the availability of soil nitrogen to plants have led to development of the following procedure which appears suitable for routine analysis of soils.

AN EVALUATION OF NITROGEN SOIL TEST METHODS FOR ONTARIO SOILS

Several methods for providing an index of the availability of soil nitrogen were evaluated by relating laboratory soil test values to yields of dry matter and uptake or nitrogen by orchardgrass in the greenhouse. Determination of soil organic matter or total soil nitrogen contents was relatively ineffective. Available nitrogen initially present in the soil at sampling time, extracted by several different methods, was superior to measurements of nitrogen released upon incubation. The nitrate form of nitrogen, either initially present or released upon incubation, served as a better index of soil nitrogen availability than the ammonium form. Inclusion of initial nitrates and nitrates released upon incubation as independent variables in a multiple regression resulted in the highest correlation with total nitrogen uptake. In the three incubation methods evaluated, discarding the initial nitrogen content of the soil, as is commonly done, severely reduced the validity of the tests as measures of nitrogen availability.

Ammonium Production in Soil under Waterlogged Conditions as an Index of Nitrogen Availability

MANY methods of obtaining an index of the availability of soil nitrogen to plants have been proposed, but it is generally accepted that the most satisfactory methods currently available are those involving estimation of the mineral nitrogen formed when soil is incubated under conditions which promote mineralization of the organic forms of soil nitrogen by soil micro-organisms1,2. Numerous incubation techniques have been used for estimation of mineralizable soil nitrogen, but methods involving determination of the nitrate produced by incubation under aerobic conditions at 28°–35° C for 2–4 weeks have been generally preferred2. However, recent work has shown that these nitrate-product ion methods are open to serious criticisms, and that the total mineral nitrogen produced during incubation should be determined2. Also, the use of aerobic incubation techniques is complicated by problems in establishment and maintenance of satisfactory conditions of incubation1,2. In an attempt to eliminate these problems and to develop an incubation method of estimating mineralizable nitrogen that is suitable for routine analysis of soils, we have investigated the possibility that methods involving estimation of the ammonium produced by incubation of soil under waterlogged conditions may provide an index of nitrogen availability. This investigation led to development of the following method of assessing mineralizable soil nitrogen: