Nitrogen Balance Calculations Research Articles

Nitrogen transformations and balance in a constructed wetland for nutrient-polluted river water treatment using forage rice in Japan

A pilot-scale surface-flow wetland planted with a new rice variety ( Oryza sativa ’Kusahonami’) developed for livestock feed was constructed for treating nutrient-polluted river water. To calculate the balance between nitrogen removal and rice plant uptake of nitrogen, nitrogen removal from river water and nitrogen interactions among plants, soil water, and soil were investigated for this constructed wetland over two growing seasons in 2004 and 2005. The constructed wetland removed 33% of the total nitrogen entering with the river water. Rice plants were found to constitute the major nitrogen storage, with plant uptake being the major removal mechanism. The total inorganic nitrogen concentration in the rhizosphere changed seasonally because of plant uptake. Most nitrogen taken up by rice plants was contained in the aboveground biomass, with the mean amount being 34.0 g N m −2. However, the nitrogen balance calculation suggested that rice plants uptake some nitrogen from soil, decreasing the available nitrogen in the soil of the lined impermeable wetland.

Nitrogen balance, protein loss, and the open abdomen*

Goal-directed nutritional support is essential to improving morbidity and mortality. Open abdominal decompression is similarly crucial to the successful treatment of intra-abdominal hypertension and abdominal compartment syndrome. The open abdomen, however, places the patient at risk for potentially significant fluid, electrolyte, and presumably protein losses from the exposed viscera. Although nutritional protein assessments are frequently utilized to measure urinary nitrogen, these calculations do not consider the loss of protein from the open abdomen. We hypothesize that accurate assessment of nitrogen balance in the patient requiring an open abdomen must include either a measurement or estimation of abdominal fluid nitrogen loss. Prospective, observational cohort study. Adult surgical/trauma intensive care unit of a level I trauma center. Surgical/trauma patients requiring laparotomy. Serial 24-hr collections of urine and abdominal fluid protein were performed to characterize abdominal fluid protein loss and evaluate the clinical effect of accounting for abdominal fluid nitrogen as part of nitrogen balance calculations. Nitrogen intake correlates with urinary nitrogen loss but not with abdominal fluid nitrogen loss. Abdominal fluid nitrogen loss is significant and remains relatively stable in the early postoperative period. Nutritional calculations that fail to account for abdominal fluid nitrogen loss significantly overestimate actual nitrogen balance by an average of 3.5 g/24 hrs. The open abdomen represents a significant source of protein/nitrogen loss in the critically ill. Failure to account for this loss in nutritional calculations may lead to underfeeding and inadequate nutritional support with a direct effect on patient outcome. Although direct measurement of abdominal fluid protein loss may be optimal, an estimate of 2 g of nitrogen per liter of abdominal fluid output should be included in the nitrogen balance calculations of any patient with an open abdomen.

Cover crop effects on the fate of N following soil application of swine manure

Cereal grain cover crops increase surface cover, anchor corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) residues, increase infiltration, reduce both rill and interrill erosion, scavenge excess nutrients from the soil, and are easily obtained and inexpensive com- pared to other cover crop options. The use of cereal grain cover crops in fields where manure application occurs should increase nitrogen (N) recovery and cycling for use in subsequent crops. The objectives of this study were to determine if a rye (Secale cereale L.) cover crop increases N retention after soil application of swine lagoon slurry. Experiments were conducted in a con- trolled environment chamber using plastic buck- ets as the experimental units. Three manure-N loading rates (no manure, low, high) were applied to soils with and without a rye cover crop. A partial N balance was determined from measure- ments of NO3 leaching, N2 Oa nd NH 3 emissions, cover crop N uptake, and NO3 +N H 4 remaining in the soil. Cumulative nitrate load in the drain- age water was less than 0.31 g m -2 NO3-N for rye treatments regardless of the manure rate, how- ever in the fallow treatments, at the high manure rate NO3 leaching losses were 6.28 and 3.77 g m -2 NO3-N, for experiments 1 and 2, respectively. Rye N uptake ranged from 2.95 g N m -2 to 10.7 g N m -2 , and was related to manure rate. Rye had lower cumulative N2O emission than the no rye treatment for the high manure treatment. Ammonia emissions were low for all treatments during both experiments, which was probably related to the rapid manure incorporation after application. Rye can increase N retention, reduce cumulative N2O emissions, and reduce cumula- tive N load in drainage water when manure is applied to soils. Nitrogen balance calculations in the cover crop treatments accounted for less than the equivalent of 50% of the added manure N. We speculate that the living rye plants may have increased immobilization of N in the organic N pools.

Cross compliance of the Water Framework and Nitrate directives in Slovenia

We describe the first characterisation of the Slovene waters and show cross compliance of the Nitrate and Water Framework Directives in Slovenia. Point and disperse sources of pollution are identified, hydrological and morphological pressures to surface water bodies evaluated and impact of all pressure to water bodies analysed. Agricultural activities in Slovenia are described and results of calculation of nitrogen and phosphorus balance in the catchment areas of the water bodies presented. The analyses show that hydro-morphological and chemical pressures from point pressures and diffused pollution from agriculture are the main reasons for the non-attainment of environmental objectives. Though consumption of mineral fertilisers and plant nutrients in Slovenia has reached more or less steady state in the last years, the quantities are still too high to reduce the risk to water environment. Therefore, the measures for reasonable fertiliser applications should be developed into more details as to give more directions for a farm level management. Miscellaneous instruments should also be developed to initiate overall sustainable use of fertilisers and plant nutrients in agriculture.

Evaluation of nitrogen balance on pig/crop farm systems in Jiulong River watershed, China

Field surplus nitrogen and farm disposal nitrogen (N) are major sources of environmental pollution in farm systems. The purpose of this study was to use nitrogen balances at the field and farm level approaches to estimate the effects of pig production in the Jiulong River watershed, Fujian province, China, on nitrogen losses to the environment on 67 pig farms. The field surplus nitrogen ranged from 6.19 to 18.19 t nitrogen ha−1, which was caused by high pig density and excessive application of manure. Manure application rates of more than 450 to 510 kg nitrogen ha −1 would increase the potential nitrate concentration to more than 10 to 20 mg l −1. Therefore, 44 to 48 heads of pig ha −1 was suggested to as the environmental capacity for sustaining optimal nitrogen cycling in pig farms in the Jiulong River watershed. The majority of farms have potential environmental risks because of high farm nitrogen imbalances. With more than a 2:1 ratio of N inputs to outputs, N inputs were 50 percent higher than outputs. Feed was the main input source, while pig production and manure exported were the major managed outputs. Based on the farm nitrogen balance calculation, the management options that would contribute to a more favorable nitrogen balance were also identified.

Nitrogen removal enhanced by intermittent operation in a subsurface wastewater infiltration system

A pilot subsurface wastewater infiltration system filled with a mixed soil of red clay + 25% cinder was constructed in a village located in Dianchi valley in south west China to treat rural sewage. At first, the system was continuously fed with rural sewage at a hydraulic loading of 2 cm d −1 for over 4 months. The removal of COD, T-P, NH 4 +-N, and T-N over the operation period was achieved at average rates of 82.7, 98.0, 70.0, and 77.7%, respectively. Compared to T-P removal, the lower nitrogen removal rates were attributed to reductive soil condition in the system, which was unfavorable for the nitrification process. An intermittent operation was adopted to improve nitrogen removal. The same performances of COD and T-P removal were achieved in the intermittent operation mode. NH 4 +-N removal was increased from 70% in the continuous feeding mode to over 90%, and T-N removal rate was elevated over 80% even with the average hydraulic loading as high as 8 cm d −1. Nitrogen balance calculation suggested that nitrification–denitrification was the main mechanism of nitrogen removal that eliminated 57–76% of the fed T-N. Soil redox potential measurement showed that the oxidative environment was increased through intermittent operation, encouraging nitrification. Correspondingly, soil nitrification potential was increased from less than 0.8 mg-N kg −1 h −1 in the continuous feeding mode to about 1.6 mg-N kg −1 h −1 in the intermittent operation mode.

Nitrogen utilization in a vapor-phase biofilter

The effect of media nitrogen levels on biofilter performance was investigated in a lab-scale biofilter treating toluene and p-xylene. Nitrogen utilization rates and the quantity of nitrogen recycled to meet microbial demand in the biofilm were estimated using a nitrogen balance approach. Experimental data imply that overall biofilter performance was a strong function of normalized nitrogen levels in the synthetic media. The biodegradation of p-xylene was found to be more sensitive to media nitrogen levels than was the degradation of toluene. However, increasing the nitrogen supply improved both toluene (>99%) and p-xylene removal efficiencies (>90%). Nitrogen balance calculations indicate that substantial recycling of nitrogen occurred in the biofilm even under nitrogen-rich conditions. The fraction of nitrogen demand met by recycling nitrogen increased when the external supply of nitrogen was terminated, and the biofilm became nitrogen limited. However, to avoid severe nitrogen limitation conditions, an external nitrogen source must be provided to sustain high pollutant removals in the biofilter.

Real-time Measures of Canopy Size as a Basis for Spatially Varying Nitrogen Applications to Winter Wheat sown at Different Seed Rates

Experiments at two sites growing winter wheat show that in order to manage a wheat canopy more effectively, the use of specific remote sensing techniques both to monitor crop canopy expansion, and to determine variable nitrogen applications at key timings is required. Variations in seed rate were used to achieve a range of initial crop structures, and treatments were compared to standard farm practice. In the first year, the effect of varying seed rate (250, 350 and 450 seeds m −2) on crop structure, yield components and grain yield, was compared to the effects of underlying spatial variation. Plant populations increased up to the highest rate, but shoot and ear populations peaked at 350 seeds m −2. Compensation through an increased number of grains per ear and thousand grain weight resulted in the highest yield and gross margin at the lowest seed rate. In later experiments, the range of seed rates was extended to include 150 seeds m −2, each sown in 24 m wide strips split into 12 m wide halves. One half received a standard nitrogen dose of 200 kg [N] ha −1, the other a variable treatment based on near ‘real-time’ maps of crop growth. Both were split into three applications, targeted at mid-late tillering (early March), growth stages GS30-31 (mid April) and GS33 (mid May). At each timing, calibrated aerial digital photography was used to assess crop growth in terms of shoot population at tillering, and canopy green area index at GS30-31 and GS33. These were compared to current agronomic guidelines. Application rates were then varied below or above the planned amount where growth was above- or below-target, respectively. In the first field, total nitrogen doses in the variable treatments ranged from 188 to 243 kg [N] ha −1, which gave higher yields than the standards at all seed rates in the range 0·36–0·78 t ha −1 and gross margins of £17 to £60 ha −1. In the second field, variable treatments ranged from 135 to 197 kg [N] ha −1 that resulted in lower yields of −0·32 to +0·30 t ha −1. However, in three out of the four seed rates, variable treatments produced higher gross margins than the standard, which ranged from £2 to £20 ha −1. In both fields, the greatest benefits were obtained where the total amount of applied nitrogen was similar to the standard, but was applied variably rather than uniformly along the strips. Simple nitrogen balance calculations have shown that variable application of nitrogen can have an overall effect on reducing the nitrogen surplus by one-third.

Nitrogen losses from outdoor pig farming systems

Abstract. Nitrogen losses via nitrate leaching, ammonia volatilization and nitrous oxide emissions were measured from contrasting outdoor pig farming systems in a two year field study. Four 1‐ha paddocks representing three outdoor pig management systems and an arable control were established on a sandy loam soil in Berkshire, UK. The pig management systems represented: (i) current commercial practice (CCP) ‐ 25 dry sows ha−1 on arable stubble; (ii) ‘improved’ management practice (IMP) ‐ 18 dry sows ha−1 on stubble undersown with grass, and (iii) ‘best’ management practice (BMP) 12 dry sows ha−1 on established grass. Nitrogen (N) inputs in the feed were measured and N offtakes in the pig meat estimated to calculate a nitrogen balance for each system. In the first winter, mean nitrate‐N concentrations in drainage water from the CCP, IMP, BMP and arable paddocks were 28, 25, 8 and 10 mg NO3 l−1, respectively. On the BMP system, leaching losses were limited by the grass cover, but this was destroyed by the pigs before the start of the second drainage season. In the second winter, mean concentrations increased to 111, 106 and 105 mg NO3‐N l−1 from the CCP, IMP and BMP systems, respectively, compared to only 32 mg NO3‐N l−1 on the arable paddock. Ammonia (NH3) volatilization measurements indicated that losses from outdoor dry sows were in the region of 11 g NH3‐N sow−1 day−1. Urine patches were identified as the major source of nitrous oxide (N2O) emissions, with N2O‐N losses estimated at less than 1% of the total N excreted. The nitrogen balance calculations indicated that N inputs to all the outdoor pig systems greatly exceeded N offtakes plus N losses, with estimated N surpluses on the CCP, IMP and BMP systems after 2 years of stocking at 576, 398 and 264 kg N ha−1, respectively, compared with 27 kg N ha−1 on the arable control. These large N surpluses are likely to exacerbate nitrate leaching losses in following seasons and make a contribution to the N requirement of future crops.

Heterotrophic nitrification by a thermophilicBacillusspecies as influenced by different culture conditions

The nitrification activity of a thermophilic heterotrophic bacterium, Bacillus MS30 isolated from a deep-sea hydrothermal vent, was studied under various growth conditions. Nitrification was estimated from the nitrogen balance calculations in the culture media. The results showed that this isolate actively nitrified in culture conditions similar to those prevailing in hydrothermal sites. Therefore, its ecological significance was considered. In standard aerobic conditions, MS30 produced nitrite from ammonia and acetate (1.13 µmol NO2-·mg-1dry wt), but nitrate was never produced, and a low nitrite reduction was often observed. Higher nitrification activities were observed in defined optimal conditions (simple carbon substrate, 65°C, pH 7.5, and 15 g sea salts · L-1). In addition, discrepancies between the optima for growth and nitrification were observed, showing the ability of MS30 to adapt to changing environmental conditions typical of hydrothermal sites.Key words: thermophilic bacteria, heterotrophic nitrification, environmental parameters.

Heterotrophic nitrification by a thermophilic <i>Bacillus</i> species as influenced by different culture conditions

The nitrification activity of a thermophilic heterotrophic bacterium, Bacillus MS30 isolated from a deep-sea hydrothermal vent, was studied under various growth conditions. Nitrification was estimated from the nitrogen balance calculations in the culture media. The results showed that this isolate actively nitrified in culture conditions similar to those prevailing in hydrothermal sites. Therefore, its ecological significance was considered. In standard aerobic conditions, MS30 produced nitrite from ammonia and acetate (1.13 mumol NO2-.mg-1 dry wt), but nitrate was never produced, and a low nitrite reduction was often observed. Higher nitrification activities were observed in defined optimal conditions (simple carbon substrate, 65 degrees C, pH 7.5, and 15 g sea salts.L-1). In addition, discrepancies between the optima for growth and nitrification were observed, showing the ability of MS30 to adapt to changing environmental conditions typical of hydrothermal sites.

Nitrogen excretion by farm livestock with respect to land spreading requirements and controlling nitrogen losses to ground and surface waters. Part 1: cattle and sheep

In this paper, published and unpublished information on excretion by dairy cattle, beef cattle and sheep is reviewed. A number of factors are known to affect both the amount and N content of livestock excreta, most notably animal liveweight, diet and water intake and, for adults, whether in lactation or not. Relationships between liveweight and the volume and N output of excreta have been used to derive estimates for `standard' outputs for a range of adult and young stock; in the case of breeding stock, allowing for the lactation period. An alternative approach for estimating N excretion, via nitrogen balance calculations, was undertaken for a number of livestock categories and provides some validation of the standards, increasing confidence in their application. These standards are now incorporated into the guidelines already in place for Nitrate Vulnerable Zones in England and Wales and in the recently revised Code of Good Agricultural Practice for the Protection of Water.

An Assessment of Nitrate Occurrence and Transport in Washoe Valley, Nevada

Using an unsewered subdivision in western Nevada as a field site, the occurrence and transport of nitrate from septic tanks was first studied using nitrogen and nitrate mass balance calculations, and was then simulated by using a solute transport model (MT3D) for two different input scenarios. The results from the transport simulations are compared with the results from the mass balance calculations, which predict that average nitrate concentrations are rarely above the federal drinking water standard of 10 mg/l NO 3 -N in the study area. The simulation using a uniform nitrogen-to-nitrate conversion ratio provides greater detail of nitrate behavior, but results are not compatible with observed values in portions of the study area. Hydrogeochemical data suggest that the study area is characterized by zones of contrasting redox conditions and associated contrasts in nitrogen speciation. These variable geochemical conditions provide the basis for regionalizing nitrogen→nitrate conversion ratios in the simulations. Resulting simulations are improved, and agree better with observed field data. We also address the capabilities and limitations of transport simulations. The limitations of simulations originated from the incomplete input information related to field conditions even though the adopted models (MODFLOW and MT3D) are robust themselves.

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.

Effects of repeated straw incorporation on crop fertilizer nitrogen requirements, soil mineral nitrogen and nitrate leaching losses

Abstract. The effects of straw disposal by burning and incorporation on soil and crop nitrogen (N) supply, were investigated on two light textured soils in central (ADAS Gleadthorpe) and eastern England (Morley Research Centre) over the period 1984 to 1995. Nitrogen balance calculations showed that after 11 years of contrasting straw incorporation versus burn treatments, the cumulative N returns in straw were c. 570kg/ha at Gleadthorpe and c. 330 kg/ha at Morley However, these N returns via straw incorporation were not reflected in increased total soil N levels in autumn 1994. There were no differences (P > 0.05) between straw disposal treatments in autumn soil mineral N supply, readily mineralizable N or organic carbon. Similarly, there were no consistent differences between the treatments in terms of crop yield, crop N uptake or optimum fertilizer N rates. Fertilizer N applications of 200 kg N/ha/y increased topsoil organic carbon from 1.18 to 1.28% and total N content from 0.091 to 0.102% on the loamy sand textured soil at ADAS Gleadthorpe, but not at Morley. Previous fertilizer N applications increased the quantity of nitrate‐N leached in drainage water by c. 20 kg/ha at Gleadthorpe and c. 60 kg/ha at Morley overwinter 1994/95, and by 10–20 kg/ha at both sites overwinter 1995/96. There was some indication overwinter 1994/95 that straw incorporation reduced nitrate‐N leaching by 10–25 kg/ha, but there were no differences between treatments overwinter 1995/96.

Chemiluminescent measurement of total urinary nitrogen for accurate calculation of nitrogen balance

This instrumental method for total urinary nitrogen (TUN) is based on the principle of gas-phase chemiluminescence. Results correlate well with measurements of TUN by the Kjeldahl method, which has long provided the means to calculate nitrogen balances for nutritional management. In recent years, because of speed and convenience of measurement, determination of urinary urea nitrogen (UUN) has been substituted for Kjeldahl TUN. However, in patients requiring aggressive nutritional support, the UUN may not be a valid indicator of total nitrogen excretion. We compared nitrogen balances calculated for patients, using both UUN and chemiluminescence TUN data. For both normal and hospitalized populations, nitrogen balance calculated from UUN data exceeded that calculated from TUN data. We show that use of UUN data in calculating nitrogen balance may result in an incorrect assessment of many patients as being in positive nitrogen balance. TUN determined by chemiluminescence evidently provides a simple means of calculating nitrogen balance more nearly accurately.

Growth ofNitrobacterby dissimilatoric nitrate reduction

Eight strains of the genus Nitrobacter grew under anaerobic conditions in the presence of nitrate. The growth was inhibited by nitrate concentrations above 0.5 mM. By a special culture technique inhibition caused by nitrite was abolished. Nitrate oxidizing cells grew in gas tight culture flasks as a biofilm on a gas-permeable silicone tubing. The biofilm allowed nitrate-reducing cells to grow at a low nitrite concentration. These cells grew either actively motile in the anaerobic medium, or in anaerobic zones of the biofilm. They produced nitrite and ammonia. Nitrogen balance calculations established a loss of inorganic nitrogen for 5 of 8 strains. This implies that nitrate-reducing cells produced furthermore volatile nitrogen compounds. N2O was detected by gas chromatography.

Estimation of nitrogen balance based on a six-hour urine collection in infants.

The accuracy of a 6-hr vs a 24-hr urine collection for the determination of urinary urea nitrogen was studied in 15 infants. Patient's age ranged from 2 weeks to 3 yr, encompassing a wide variety of diagnoses. All patients had normal renal function at the time of the study. Participants had indwelling foley catheters throughout the study. Urine specimens were collected over a continuous 24-hr period. Aliquots obtained from urine collected over 0 to 6 hr and the total urine collection were analyzed utilizing the urease enzymatic method in the Astra. Statistical analysis was performed comparing the actual 24-hr determination to the estimation based on the 6-hr collection, utilizing linear regression. The analysis of data produced a highly significant correlation (r = 0.904, p less than 0.0001). When a 24-hr urine collection is not possible, a 6-hr collection is a useful alternative for the calculation of nitrogen balance in infants.

A simple method for estimating nitrogen balance in hospitalized patients: a review and supporting data for a previously proposed technique.

Total urinary nitrogen (TUN) and urinary urea nitrogen (UUN) in a 24-hour urine collection were measured under a variety of clinical and nutritional conditions in 81 patients for 564 study days. The difference between TUN and UUN averaged 1.8 +/- 0.9 g/day (range 0.0-5.8 g/day) and was independent of the absolute value for UUN. Since UUN was found to correlate linearly with TUN (R = 0.98) over a wide range of values, it is possible to estimate an approximate TUN excretion by adding a constant to the nitrogen excreted as urea. On the basis of the measured mean difference, we suggest using an estimate of 2 g of nitrogen per day. We feel this will not seriously under- or overestimate urinary nitrogen excretion in the calculation of nitrogen balance for the clinical management of nutritional support therapies. Since all hospitals can perform this routine test, it provides an effective, simple, and rapid method to follow accurately the protein catabolic response during disease and response to nutritional therapy. This method, without the supporting data presented here, has previously been recommended [Blackburn et al, 1977, JPEN 1:11-22] and has become a widely used technique for nutritional assessment.

Fate of glutamate carbon and nitrogen in isolated guinea-pig kidney-cortex tubules. Evidence for involvement of glutamate dehydrogenase in glutamine sythesis from glutamate.

1. The pathways and the fate of glutamate carbon and nitrogen were investigated in isolated guinea-pig kidney-cortex tubules. 2. At low glutamate concentration (1 mM), the glutamate carbon skeleton was either completely oxidized or converted into glutamine. At high glutamate concentration (5 mM), glucose, lactate and alanine were additional products of glutamate metabolism. 3. At neither concentration of glutamate was there accumulation of ammonia. 4. Nitrogen-balance calculations and the release of 14CO2 from L-[1-14C]glutamate (which gives an estimation of the flux of glutamate carbon skeleton through alpha-oxoglutarate dehydrogenase) clearly indicated that, despite the absence of ammonia accumulation, glutamate metabolism was initiated by the action of glutamate dehydrogenase and not by transamination reactions as suggested by Klahr, Schoolwerth & Bourgoignie [(1972) Am. J. Physiol. 222, 813-820] and Preuss [(1972) Am. J. Physiol. 222, 1395-1397]. Additional evidence for this was obtained by the use of (i) amino-oxyacetate, an inhibitor of transaminases, which did not decrease glutamate removal, or (ii) L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which caused an accumulation of ammonia from glutamate. 5. Addition of NH4Cl plus glutamate caused an increase in both glutamate removal and glutamine synthesis, demonstrating that the supply of ammonia via glutamate dehydrogenase is the rate-limiting step in glutamine formation from glutamate. NH4Cl also inhibited the flux of glutamate through glutamate dehydrogenase and the formation of glucose, alanine and lactate. 6. The activities of enzymes possibly involved in the glutamate conversion into pyruvate were measured in guinea-pig renal cortex. 7. Renal arteriovenous-difference measurements revealed that in vivo the guinea-pig kidney adds glutamine and alanine to the circulating blood.