Sparse Crops Research Articles

Analysis of Water Budgets in Semi-Arid Lands from Soil Water Records

SUMMARYFour components of the water budget for a growing season, namely storage, drainage, transpiration and direct evaporation from the soil surface, were estimated using a suite of techniques. The only data requirements were rainfall, neutron probe measurements of soil water content and microlysimeter measurements of evaporation from the soil. Data from four growing seasons at Kiboko, Kenya between 1990 and 1992 were used to provide examples of the estimations. Drainage was significant (about 10% of rainfall) in one season only; in the other seasons, total evaporation comprised at least 95% of the seasonal rainfall.Drainage was determined using a relationship between unsaturated hydraulic conductivity and soil water content that was determined during the early part of the rainy season when water was penetrating to depth. This analysis made it possible to identify a critical water content at the base of the soil profile, above which there would be significant drainage. However, there are large errors associated with estimation of drainage if significant drainage occurs.Estimates of direct evaporation from the soil surface were used as the basis of distinguishing transpiration from total evaporation. Microlysimetry was used to develop a model of evaporation from these sandy soils, which was based on the assumption that the evaporation from the soil surface following heavy rainfall is a unique function of time from rainfall, and little influenced by the presence of a sparse crop. This method showed that direct evaporation from the soil accounted for between 70 and 85% of total evaporation in seasons when total evaporation estimates ranged from 150 to 325 mm.

Transpirational cooling of a greenhouse crop with partial ground cover

The well-being of sparsely planted seedlings in greenhouses under high energy loads is a matter of concern, since transpirational (cooling) flux of the small plants is rather limited. A simplified analysis of the problem suggests the following conclusions. 1. (1) If water supply to the stomata is not limiting, then, for a given ventilation rate, the canopy temperature of a sparse (young) crop should normally not be higher than that of a dense (mature) crop. 2. (2) For a given canopy temperature, sparse plants transpire more per unit leaf area, due to micro-advection of energy ‘surplus’ from the surrounding bare and dry ground (local oasis effect). 3. (3) High foliar potential transpiration may lead to water stress. Relieving this stress may justify control measures, such as artificial evaporative cooling or increased ground albedo. 4. (4) Artificial evaporative cooling (e.g. wet pad), is only effective when stomatal resistance is considerable and outside air is dry. 5. (5) Temporary storage of heat in passive systems has a cooling effect similar to increased ground albedo.

Parameterisations for energy transfers from a sparse vine crop

Parameterisations are presented for the energy budget of a sparse vine crop growing under semi-arid conditions in southern Spain. The measurements were made as part of the European Field Experiment in a Desertification-threatened Area (EFEDA) project which has as one of its main aims the development of regional scale land-atmosphere models appropriate to sparse crops and natural vegetation growing under these conditions. The results presented here should prove useful to this objective as well as providing information of more general interest for modelling sparse crops. All of the main components in the energy balance were recorded, including the sensible and latent heat fluxes which were measured using eddy correlation equipment. The measurements were made over the first 50 days of plant growth during which the plant area coverage increased from zero to about 30%. Over this period, 18 mm of rainfall was recorded and the maximum soil moisture content reached was about 5% in the 0–5cm surface layer. The measurements have been interpreted within the framework of the Shuttleworth—Wallace energy combination model. The roughness length increased from about 0.01 m to 0.04–0.06 m for the fully grown vines and peak daily bulk canopy conductances increased from about 0.5 mm s −1 to 1.5 mm s −1. Results are also presented for the influence of plant growth and variations in soil moisture on the overall available energy and the energy partition between the plants and bare soil. The models suggest that, of the total observed evaporation of 69 mm, approximately 45 mm could be attributed to plant transpiration with the remainder arising from the bare soil.

A comparative study of mass and energy exchange over a closed C 3 (wheat) and an open C 4 (corn) canopy: I. The partitioning of available energy into latent and sensible heat exchange

Eddy correlation measurements of mass and energy were made simultaneously over a closed wheat and an open corn crop. This combination of crops, differing in canopy coverage and stomatal physiology, facilitated an investigation on how surface and environmental variables control the partitioning of net radiation into sensible, latent and soil heat exchange. Contrasts in canopy closure had a minor affect on the flux densities of net radiation ( R n) measured over open corn and closed wheat canopies. On the other hand, differences in canopy closure perturbed the partitioning of net radiation into sensible, latent and soil heat exchange. On average, measurements of latent heat flux densities ( LE) over the sparse corn canopy were 59% less than LE measured over the closed wheat crop. Compensation for this bias caused greater flux densities of sensible ( H) and soil ( G) heat to be generated from the sparse corn canopy. Sensible heat flux densities were, on average, 22% greater over the open corn canopy. During the day, soil heat flux densities were, on average, 64% greater under the corn canopy than under the wheat. Available energy ( A) governed daytime latent heat flux densities over the closed wheat canopy. Consequently, LE was proportional to equilibrium evaporation rates ( LE eq). When the corn canopy was dry, latent heat flux densities were less coupled to available energy ( A). This response occurred because exposed soil and the corn's C 4 physiology increased the corn's canopy resistance to water vapor transfer. When the sparse corn canopy was wet, LE approached values experienced by the closed wheat canopy. A rule of thumb, explaining the surface control of latent heat exchange, was extracted from these data. The ratio between LE and LE eq diminished linearly with logarithmic increases of surface resistance. Different processes controlled canopy evaporation at night. Nocturnal evaporation flux densities measured over the closed wheat crop were independent of available energy, and instead were a function of the atmosphere's vapor pressure deficit. Evaporation flux densities measured over the sparse crop were weakly dependent on available energy.

A multiple-source land surface energy balance model for use in general circulation models

A multiple-source surface energy balance model for use in general circulation models (GCMs) is developed. The model recognizes three biome architectures: closed canopies (e.g. forest), biomes with two distinct canopies (e.g. savannah) and agricultural crops. The model is based on the Penman-Monteith approach and solves for latent and sensible heat flux without the need to specify a surface temperature or humidity. The two canopies and soil layer are allowed to interact through the specification of a within-canopy saturation deficit and temperature. One or two canopy surface resistances and a soil surface resistance can be specified. The model is calibrated for tropical rainforest, tropical savannah and an agricultural crop. Good agreement is obtained for both hourly and long term evaporation. Two responses to soil moisture were identified for the savannah: a long term one and a short term one. The latter relates to the switching of evaporation from a demand controlled to a supply controlled process. Some problems in the specification of roughness lengths for sparse crops lead to errors in the calculation of momentum exchange. Suggestions are made for improvement. Possible applications of the model are discussed.

Comparison of Penman‐Monteith, Shuttleworth‐Wallace, and Modified Priestley‐Taylor Evapotranspiration Models for wildland vegetation in semiarid rangeland

Eddy correlation measurements of sensible and latent heat flux are used with measurements of net radiation, soil heat flux, and other micrometeorological variables to develop the Penman‐Monteith, Shuttleworth‐Wallace, and modified Priestley‐Taylor evapotranspiration models for use in a sparsely vegetated, semiarid rangeland. The Penman‐Monteith model, a one‐component model designed for use with dense crops, is not sufficiently accurate (r2 = 0.56 for hourly data and r2 = 0.60 for daily data). The Shuttleworth‐Wallace model, a two‐component logical extension of the Penman‐Monteith model for use with sparse crops, performs significantly better (r2 = 0.78 for hourly data and r2 = 0.85 for daily data). The modified Priestley‐Taylor model, a one‐component simplified form of the Penman potential evapotranspiration model, surprisingly performs as well as the Shuttle worth‐Wallace model. The rigorous Shuttleworth‐Wallace model predicts that about one quarter of the vapor flux to the atmosphere is from bare‐soil evaporation. Further, during daylight hours, the small leaves are sinks for sensible heat produced at the hot soil surface.

Energy budgets and resistances to energy transport in sparsely vegetated rangeland

Partitioning available energy between plants and bare soil in sparsely vegetated rangelands will allow hydrologists and others to gain a greater understanding of water use by native vegetation, especially phreatophytes. Standard methods of conducting energy budget studies result in measurements of latent and sensible heat fluxes above the plant canopy which therefore include the energy fluxes from both the canopy and the soil. One-dimensional theoretical numerical models have been proposed recently for the partitioning of energy in sparse crops. Bowen ratio and other micrometeorological data collected over phreatophytes growing in areas of shallow ground water in central Nevada were used to evaluate the feasibility of using these models, which are based on surface and within-canopy aerodynamic resistances, to determine heat and water vapor transport in sparsely vegetated rangelands. The models appear to provide reasonably good estimates of sensible heat flux from the soil and latent heat flux from the canopy. Estimates of latent heat flux from the soil were less satisfactory. Sensible heat flux from the canopy was not well predicted by the present resistance formulations. Also, estimates of total above-canopy fluxes were not satisfactory when using a single value for above-canopy bulk aerodynamic resistance.

Aerodynamic and surface resistances affecting energy transport in a sparse crop

Aerodynamic and surface properties of the soil and canopy affect energy transport within sparse crops. A study was conducted with cotton ( Gossypium hirsutum L.) to evaluate the feasibility of using both surface and within-canopy resistances to describe heat and water vapor transport from a row crop at partial cover. Bowen ratio measurements of the field energy balance and stem flow measurements of transpiration were coupled with detailed radiation measurements to determine sensible and latent heat flux from the soil and canopy separately. Flux measurements were combined with point measurements of temperature and vapor density to calculate the surface and aerodynamic resistances to heat and vapor transport using a one-dimensional model. The characteristics of the soil and canopy were described with bulk parameters, and a hypothetical within-canopy airstream was employed to model transport between the surface and the within-canopy air. Micrometeorological estimates of canopy surface resistance to vapor transport were similar in magnitude and behavior to data reported for full canopies. Computed values of soil surface resistance to vapor transport increased as the soil dried, reaching a maximum value of 1578 s m −1. However, results suggest that a sophisticated soil surface model will be needed to accurately quantify a diffusive soil resistance. An alternate approach for describing soil evaporation yielded more favorable results, in which soil water potential and temperature were used to estimate the vapor concentration at the immediate soil surface, eliminating the need for a diffusive soil resistance. Within-canopy aerodynamic and surface resistances had equal influence on vapor transport from the canopy. Aerodynamic resistances to transport from the soil surface were greater than those for the canopy at low wind speeds. All aerodynamic resistances tended to decrease as wind speed increased. However, calculated within-canopy aerodynamic resistances were highly variable and could not be adequately described by average wind speed, wind direction or canopy size. This study indicates that within-canopy transport from the soil and canopy cannot be partitioned or quantified using simple gradient diffusion relationships in combination with standard meteorological data.

Determination of soil water evaporation and transpiration from energy balance and stem flow measurements

Frequent measurements of soil water evaporation ( E) and transpiration ( T) are needed to quantify energy and water balances of sparse crops. Field experiments were conducted in Lubbock, TX to examine the feasibility of partitioning evapotranspiration ( ET) from a cotton crop ( Gossypium hirsutum L.) during periods of partial cover. The Bowen ratio energy balance method and heat balance stem flow measurements were used to make near-instantaneous measurements of ET and T, respectively. Transpiration on a unit land area basis was determined by normalizing stem flow measurements by leaf area or plant density. Soil water evaporation was computed as the difference between ET and T. The accuracy of the method was evaluated by comparing calculated values of E with measured values obtained from soil microlysimeters. Measurements over an 8-day period following an irrigation indicated that daily values of calculated E were within 0.5 mm of measured values in six out of seven comparisons when stem flow measurements were normalized on a leaf area basis. On average, daily calculated E was within ±11% of measured values. Calculated and measured cumulative E agreed to within 0.6 mm at the end of the evaluation period. Computing T by normalizing stem flow on a plant density basis resulted in overestimates of T and underestimates of E. Error analysis indicates that the precision of the E estimate decreases rapidly as evaporation becomes a smaller fraction of ET, and is influenced equally by the resolution of the stem flow and leaf area measurements. This study demonstrates that high frequency, independent measurements of soil and canopy evaporation can be obtained by measurement of ET and stem flow.

The theoretical relationship between foliage temperature and canopy resistance in sparse crops

One-dimensional, sparse-crop interaction theory is reformulated to allow calculation of the canopy resistance from measurements of foliage temperature. A submodel is introduced to describe eddy diffusion within the canopy which provides a simple, empirical simulation of the reported behaviour obtained from a second-order closure model. the sensitivity of the calculated canopy resistance to the parameters and formulae assumed in the model is investigated. the calculation is shown to exhibit a significant but acceptable sensitivity to extreme changes in canopy aerodynamics, and to changes in the surface resistance of the substrate beneath the canopy at high and intermediate values of leaf area index. In very sparse crops changes in the surface resistance of the substrate are shown to contaminate the calculated canopy resistance, tending to amplify the apparent response to changes in water availability. the theory is developed to allow the use of a measurement of substrate temperature as an option to mitigate this contamination.

The theoretical relationship between foliage temperature and canopy resistance in sparse crops

AbstractOne‐dimensional, sparse‐crop interaction theory is reformulated to allow calculation of the canopy resistance from measurements of foliage temperature. A submodel is introduced to describe eddy diffusion within the canopy which provides a simple, empirical simulation of the reported behaviour obtained from a second‐order closure model. the sensitivity of the calculated canopy resistance to the parameters and formulae assumed in the model is investigated. the calculation is shown to exhibit a significant but acceptable sensitivity to extreme changes in canopy aerodynamics, and to changes in the surface resistance of the substrate beneath the canopy at high and intermediate values of leaf area index. In very sparse crops changes in the surface resistance of the substrate are shown to contaminate the calculated canopy resistance, tending to amplify the apparent response to changes in water availability. the theory is developed to allow the use of a measurement of substrate temperature as an option to mitigate this contamination.

Seed‐borne cucumber mosaic virus infection of narrow‐leafed lupin (Lupinus angustifolius) in Western Australia

SUMMARYIn 1986 in Western Australia, cucumber mosaic virus (CMV) infection was widespread in breeders' selections of narrow‐leafed lupin (Lupinus angustifolius), and in collections of lupin cvs and wild L. angustifolius lines. When seed of some of these selections and cvs was sown, seed‐borne CMV was detected in seedlings. Infection of F1 progenies was traced to use of infected parent plants. CMV was also widespread in 25 seed crops of the new lupin cv. Wandoo but not in 42 seed crops of the new cv. Danja. When samples of the seed sown in 1986 were tested, CMV was detected in 3 ‐ 34% of seedlings of cv. Wandoo but in none of cv. Danja. Following intensive roguing of symptom‐bearing plants in the 1986 seed crop of new lupin cv. Gungurru, the level of seedling infection with CMV in seed samples after harvest was 0·1‐0·2%. CMV was detected in 6 ‐ 8%, 0·6‐5% and 0 ‐ 18% of seedlings from seed samples of established lupin cvs Chittick, Yandee and Illyarrie respectively. Highest levels of seed transmission were in seed from crops grown in high rainfall areas.When a sample of cv. Wandoo seed was graded for size by sieving, CMV was detected in seedlings grown from seed in all grades, but the smallest grade contained the highest level of infection. When seed was collected from pods at different positions on plants in a CMV‐infected crop of cv. Illyarrie, seed from primary pods transmitted the virus to seedlings at a 3% rate, seed from first order lateral pods at 8% while seed from second and third order lateral pods transmitted at 13%. Examination of CMV‐infected lupin crops indicated that seed‐infected plants competed poorly and tended to be shaded out in dense crops but to survive in sparse crops. In 1987 during drought conditions after seeding, plant mortality was greater with seed‐infected seedlings than with healthy seedlings despite wide plant spacing.An isolate of CMV from subterranean clover (Trifolium subterraneum) induced severer symptoms in lupins than four isolates from lupin; only the subterranean clover isolate prevented seed production. In tests at one lupin breeding site, CMV was found in 15 species of weeds and volunteer legumes. Fumaria officinalis, Stachys arvensis and volunteer lupins were most frequently infected.

Inferring stomatal resistance of sparse crops from infrared measurements of foliage temperature

A coupled two-layer model of energy partitioning between soil and foliage for application to sparse crops was used to calculate the mean stomatal resistance from infrared measurements of foliage temperature. The model was tested against diurnal measurements of stomatal resistance, made with a diffusion porometer on two contrasting plots of wheat. One plot was kept well watered (W) and the other plot was left unwatered (D) for 40 days. Soil water deficit conditions had developed on the D plot by the time of measurement. To further test the model, a sensitivity analysis of the calculated stomatal resistance for a wide range of hypothetical leaf areas, foliage temperatures and sensible heat fluxes from the soil was conducted. At 0800 hours the foliage temperature of the W plot was 0.2°C cooler than the D plot. When measurements ceased at 1600 hours the W plot was 3.7°C cooler. As a result of these temperature differences the calculated mean leaf stomatal resistance deviated little from 90 s m −1 on the W plot but increased during the day from 130 to 250 s m −1 on the D plot. These calculated values accounted for 76% of the variance measured by porometer and were close to the 1:1 relationship. The sensitivity analysis indicated the importance of using a coupled two-layer model when calculating stomatal resistance from sparse, water stressed crops. Without such a model the effects of leaf area index on bulk boundary layer resistance and sensible heat flux from soil are ignored and the calculated stomatal resistance is overestimated. This results because drying of the soil can elevate soil surface temperature causing an increase in foliage temperature without any stomatal change.

Energy and Water Balance of a Sparse Crop: Simulated and Measured Soil and Crop Evaporation

AbstractDryland crops grown in semiarid environments often do not completely cover the soil, leaving a portion of the soil surface exposed to a condition of rapid soil‐water evaporation. Quantitative separation of soil evaporation and crop transpiration is important if cultural practices or cultivars are to be evaluated. This study was designed to evaluate a combined energy and water balance model, ENWATBAL, to describe the concurrent heat and water fluxes in a row crop. Inputs to the model include soil and plant variables and daily weather data. Measurements were made for a period of 74 d over a cotton (Gossypium hirsutum L.) canopy during 1985 on an Olton soil (fine, mixed, thermic Aridic Paleustolls) at Lubbock, TX. Data collected included soil‐water content, soil temperature, root distribution, soil evaporation with microlysimeters, and leaf area index, for both an irrigated and a dryland plot. The values for daily evaporation and evapotranspiration calculated with the model were within 1 standard deviation of the measured values. Cumulative evaporation and evapotranspiration from the model agreed with measured values within 7% for the dryland and 8% for the irrigated plot. Estimated soil‐water and temperature profiles also agreed closely to measured values. Soil evaporation was found to be 30% of evapotranspiration, for both the irrigated and the dryland plot. The ENWATBAL model provides a reliable method of evaluating the effects of management practices and crop selection on the water‐use efficiency of crop production in a semiarid area.

Evaporation from sparse crops‐an energy combination theory

AbstractA one‐dimensional model is adopted to describe the energy partition of sparse crops. Theoretical development of this model yields a combination equation which describes evaporation in terms of controlling resistances associated with the plants, and with the soil or water in which they are growing. the equation provides a simple but physically plausible description of the transition between bare substrate and a closed canopy. Although the aerodynamic transfer resistances for incomplete canopies have, as yet, no experimental justification, typical values, appropriate to a specimen agricultural crop and soil, are shown to have limited sensitivity in the model. Processes which require further study if the equation is to be used to calculate evaporation throughout a crop season are also discussed.

Effects of Tillage Practices on Soil and Wheat Spectral Reflectances1

AbstractThe objective of the study, which was located on a Williams loam soil (fine‐loamy, mixed Typic Argiborolls) near Sidney, Mont., was to attempt to discriminate by reflectance determinations among varying degrees of wheat (Triticum aestivumL.) stubble and crop growth covering the soil surface. Spring and winter wheat were seeded no‐till (NT) into standing spring wheat stubble and after one tillage operation on stubble‐mulch fallow and on bare soil. Also included in the study were bare fallow, stubble‐mulch fallow, and chemical fallow. A handheld radiometer With bandpass intervals similar to those of the multispectral scanner aboard Landsat was used to measure radiances from the plots. Reflectances were calculated as the ratio of plot radiance to the radiance from a barium sulfate plate. Reflectance differences among fallow treatments were not consistent throughout the season, and it is questionable whether, with present techniques, we can discern among fallow treatments. Wheat that was seeded NT into standing stubble and wheat that was seeded after one tillage operation could be detected and separated from soil readings as early as wheat seeded on bare fallow. Sparse crop growth during a drought year could not be separated from soil background. The relationship between green leaf dry matter (DM) and IR/Red ratio suggests that reflectance measurements may substitute for manual measurements of green leaf DM.

THE ECONOMIC IMPACT OF DEER FORESTS IN THE SCOTTISH HIGHLANDS 1850 - 1914

A visitor to Scotland might be forgiven for concluding that Highland history consisted of 'The Forty-Five' and 'The Clearances'. On the shelves of popular bookshops volumes of material on these themes are available and in historical journals they appear with remarkable regularity. Yet, apart from James Hunter's work little attention has been paid to the dramatic change in land-use in the late nineteenth century as sheep farms were cleared and converted to deer forests.' This omission may be due to the fact that the direct effect on Highland society was neither as revolutionary nor as emotive as that of the Clearances. After all, the people had already been deprived of access to these lands under the sheep-farming regime and, when the flockmasters left, conversion to deer forest did not, on the whole, involve disturbance of the crofting communities. What it did produce, however, was a feeling of resentment; many crofters, particularly those living on the perimeters of the forests felt that as the land was no longer of any value for sheep farming it should be returned to them to alleviate the congestion in the townships. They could see the grass undisturbed on the deer ground and could compare it with the sparse crops on their own exhausted holdings. To add to their sense of injustice the deer often raided their arable land. This exasperation finally found expression in the Highland 2 Land League and in the occupation of several forests. The departure of the sheepfarming tenants reduced the 'middle class' section of rural society and helped to emphasise the division between landlord and crofter. These sociological effects are important but what is more significant is the long-term economic impact of deer forest development. By precluding any change of land-use which might have favoured the crofters and dealt with the fundamental problems of the North-Western

The analysis of crops and soils for the triazine herbicide cyanazine and some of its degradation products. II. Results

AbstractCrops and soils from field trials in 1967–1970 in several countries have been analysed for residues of the triazine herbicide cyanazine (‘BLADEX’Shell Registered Trade Mark. a or ‘FORTROL’a' 2‐chloro‐4‐(1‐cyano‐1‐methylethylamino)‐6‐ethylamino‐1,3,5‐triazine) and for its degradation products 2‐chloro‐4‐(1‐carbarmoyl‐1‐methylethylamino)‐6‐ethylamino‐1,3,5‐triazine (II), 2‐chloro‐4‐(1‐cyano‐1‐methylethylamino)‐6‐amino‐1,3,5‐triazine (V) and 2‐chloro‐4‐(1‐carbonyl‐1‐methylethylamino)‐6‐amino‐1,3,5‐triazine (VI).The time for the concentration of cyanazine in soils to fall to half the initial value was in the range 1.3 to 5 weeks with a mean value of 2.4 weeks. The rate of loss was not affected by sparse crop cover and there was some indication that the rate was greater under moist soil conditions.Residues of up to 0.5 part/million of (II) and up to 0.08 part/million of (VI) were detected in soils at 4 weeks from cyanazine application at 2 kg/ha. The residues of cyanazine and the degradation products declined rapidly and were 0.07 part/million or less at 16 weeks from treatment. Repeated annual applications did not lead to a detectable build up of residues in soil.Neither residues of cyanazine nor those of (II), (V) or (VI) could be detected in a wide range of crops harvested from soil treated in accordance with the likely recommendations and the limits of detectability were 0.01 to 0.04 part/million.

The Problem of Land Fragmentation in the Mediterranean Area: A Case Study

... the race between population and resources continues. The demand for more food is being met at a terrible price. Denuded hillsides, sparse crops, underfed cattle, roaming goats and the threat to the soil are a spectacular warning that the undue extension of cultivation, overgrazing and deforestation, on which the present livelihood of large numbers is based, will undermine future stability. Population in a large part of the area is growing at an almost explosive rate; the area of productive soil is shrinking from year to year, and the productivity of the soil is not increasing. Nor have the people found alternative occupations to maintain themselves. In no country was full employment provided for the urban masses, and the shocking underemployment of the rural population has not been substantially relieved.

THE MUTUAL EFFECT OF RYEGRASS AND CLOVER WHEN GROWN TOGETHER

Italian ryegrass and a late‐flowering red clover were grown together, with abundance of water and nutrients for both. It was found that even a small number of ryegrass plants reduced the growth of clover by 30%. This effect varied very little with increasing density of the clover crop.The presence of clover reduced the ryegrass crop by an amount diminishing as the density of the ryegrass was increased. In a sparse crop of ryegrass, clover reduced the growth of the grass considerably more than did barley under comparable conditions.There is no evidence of any specific effect of the roots of one plant on the other. When ample nitrogen is available the clover tends to take some that would otherwise be available for the grass and does not provide the grass with additional nitrogen.