Mikrobielle Aktivitäten in landwirtschaftlich genutzten Böden Niedersachsens. II. Bodencharakterisierung anhand mikrobieller Stoffwechselaktivitäten

Microbial activity of arable soils in Lower Saxony, Germany. II. Soil characterization by microbial activities Field trials were carried out on six soil types in Lower Saxony and were supported by glasshouse and laboratory trials. Soils were sampled frequently to monitor biomass-related and overall microbial activities as well as the activity of soil enzymes. Similar soils showed comparable activity patterns. Crop plants and, especially, the herbicide ‘Flüssig Herbogil’ (dinoterb) affected some microbial functions. Activity patterns can be used in long-term trials to characterize soil types and agricultural practices. In addition, they may be useful in short-time trials to identify ecological and ecotoxicological effects.     

Kali-Düngeempfehlung auf der Grundlage von 81 K-Düngungsversuchen zu Getreide und Zuckerrüben auf Lößböden in Südniedersachsen

K-fertilization recommendation on the foundation of 81 experiments with small grains and sugar beets on ‘loes’soils in the southern part of Lower Saxony (West Germany) In no case was it possible to increase the grain yield of winter wheat and winter barley with K-fertilization. However, in the average of 24 experiments with sugar beets, K-fertilization increased significantly the sugar yield. The amount of K-fertilization necessary for sugar beets on the single fields could not be determined by the K soil analysis. Based on these results, which were received mainly on deep rootable and many years intensively fertilized ‘loess’soils, the following K-fertilization for a crop rotation of sugar beets and 2 × small grain is recommended: Independent of the K-content of soils for sugar beets 200 kg K₂O/ha should be applied if the crop residues remain on the field. However, for small grains a mineral K-fertilization is not necessary. If the residues are not returned to the soil the amount of K contained in the residues must be additionally applied.     

Phosphat-Düngerbedarf von Getreide und Zuckerrüben im südniedersächsischen Lößgebiet

Phosphate fertilizer requirement of cereals and sugar beets on “loess soils” in the Southern part of Lower Saxony (F.R. of Germany) In the years 1984 to 1986 105 P-fertilizer experiments with winter wheat, winter barley and sugar beets were carried out on “loess soils” in the Southern part of Lower Saxony (F. R. of Germany). The mineral P fertilization applied as “Triplephosphat” varied between 0 and 250 kg P₂O₅/ha. Soil test values (P-H₂O method) of the sites ranged from 6 to 38 and were on the average 18 ± 8 mg P/kg. Besides the P-H₂O-extraction the following methods were used: CAL, DL, NaHCO₃ and EUF. In no case P-application increased yields of cereals and sugar beets, although in 1986 there was no P fertilization for three years. Results of plant analysis (0.3–0.6% P i. dm) also showed a sufficient P-status. Furthermore an increase of P content of soils (+20 mg P-H₂O/kg on average) by a fertilizer rate of 1500 kg P₂O₅/ha did not effect yield in the following years. Thus, on these fields with P levels of 5 mg P-H₂/kg soil (5 mg P₂O₅-CAL/100 g) and more a P fertilization corresponding to the P removal by the crop rotation of sugar beets and 2x cereals of about 180 kg P₂O₅/ha in three years is recommended, if crop residues remain on the field. At P levels higher than 12–14 mg P-H₂O/kg soil P fertilization can be below P-removal or omitted.     

Ein Vergleich von Eisenpodsolen im östlichen Niedersachsen mit Podsolen unter borealem Nadelwald in Finnland

Iron podzols in eastern Lower Saxony compared with podzols under finnish boreal Pine forests Well developed iron podzols with orange-brown Bs-horizons poor in humus are found in isolated small areas of eastern Lower Saxony. Because of their similarity they were compared with finnish podzols under boreal pine forest. Similar soil morphology, low humus illuviation and unconsolidized Bs-horizons are common to both groups of podzols. Different are the smaller thickness of soil horizons and the higher amounts of Fe-oxides in B-horizons of finnish podzols. Despite high grade of activity (Fe_ox/d) this may be due more to iron oxide formation by silicate weathering (micas) than to podzolization. An interpretation of the german podzols as relics from boreal coniferous forests may be supposed but there is no significant evidence by the considered datas.     

Wasseraufnahme junger Zuckerrüben in Beziehung zur Salzkonzentration der wurzelnahen Bodenlösung

Water uptake of young sugar beets in relation to the salt concentration of the rhizospheric soil solution When plants absorb soil water from saline soils salts translocated to the roots surface accumulate in the soil solution close to the roots. Due to the salt dissolved in the rhizospheric soil solution its osmotic potential is several times lower than the osmotic potential of the soil solution far from the roots thus affecting their water uptake. Shoots of young sugar beets transpired about 3,0 resp. 1 ml/h/g shoot dry matter, when the roots were surrounded by soil solutions of –0,5 MPa resp. –2,0 MPa. There was nearly no water, uptake from soil solutions of –2,5 to –3,0 MPa. Ψ-values of this range are supposed to occur only around roots of highly salt adapted sugar beets. In a wide range the water content of a sandy soil did not affect the Ψ-value preventing water uptake.     

Kinetics of the respiratory response of the soil and rhizosphere microbial communities in a field experiment with an elevated concentration of atmospheric CO2

The effect of an elevated concentration of atmospheric CO₂ and the application rate of nitrogen fertilizers on the microbial biomass and maximum specific growth rate of microorganisms in the soil and rhizosphere was studied in a long-term field experiment involving the growing of sugar beets and winter wheat. It was shown that the treatment of field plots with carbon dioxide at a concentration higher than that in the atmosphere (550 ppm) for three-four years resulted in the formation of a microbial community with a higher maximum specific growth rate and a larger share of R-strategy microorganisms as compared to the soil under the control plants. No reliable differences in the total microbial biomass in the soil under the winter wheat were revealed between the treatments with the ambient and elevated CO₂ concentrations; in the soil under the beet plants, a reliable increase in the total microbial biomass at the elevated CO₂ concentration was noted only in the close vicinity of the plant roots.     

Soil organic matter turnover as a function of the soil clay content: consequences for model applications

Based on a literature review including 201 surface soils from wet, mild, mid-latitude climates and 290 soils from the Lower Saxony soil monitoring programme (Germany), we investigated the relationship between soil clay content and soil organic matter turnover. The relationship was then used to evaluate the clay modifier for microbial decomposition in the organic matter module of the soil-plant-atmosphere model DAISY. A positive relationship was found between soil clay content and soil microbial biomass (SMB) C. Furthermore, a negative relationship was found between soil clay content and metabolic quotient (qCO₂) as an indicator of specific microbial activity. Both findings support the hypothesis of a clay dependent capacity of soils to protect microbial biomass. Under the differing conditions of practical agriculture and forestry, no or only very weak relationships were found between soil clay content and non-living soil organic matter C (humus C). It is concluded that the stabilising effect of clay is much stronger for SMB than for humus. This is in contrast to the DAISY clay modifier assuming the same negative relationship between soil clay content, on the one hand, and turnover of SMB and turnover of soil humus on the other. There is a positive relationship between SMB and microbial decomposition activity under steady-state conditions (microbial growth≈microbial death). The original concept of a biomass-independent simulation of organic matter turnover in the DAISY model must therefore be rejected. In addition to the original modifiers of organic matter turnover, a modifier based on the pool size of decomposing organisms is suggested. Priming effects can be simulated by applying this modifier. When using this approach, the original modifiers are related to specific microbial activity. The DAISY clay modifier is a useful approximation of the relationship between the metabolic quotient (qCO₂) as an indicator of specific microbial activity and soil clay content.     

Der Einfluß der Kaliumkonzentration der ‘Bodenlösung’ auf den Ertrag,den Wasserverbrauch und die K-Aufnahmearten von Zuckerrüben (Beta vulgaris ssp. esculenta var. altissima)

The effect of the potassium concentration of the “soil solution” on the yield, the water consumption and the potassium uptake rates of sugar beets (Beta vulgaris ssp. esculenta var. altissima) . 1. The object of this experiment was to investigate which K concentration of the nutrient solution can be regarded as optimal for the growth of sugar beets. The nutrient medium was a quartz sand with a nutrient solution, of which the nutrient concentration could be controlled and corrected at any time due to a newly developed technique. Compared with a solution culture this technique enables a contact surface between the roots and the soil solution, which equals more field conditions. 2. The experment had three treatments with the following K concentrations: 0.2, 1A and 5.0 me K/1. These K concentrations were controlled and corrected by K additions and were kept approximately constant during the growing period. 3. The yields of beet roots and sugar of the treatment “0.2 me K” were significantly lower than the yields of the other two treatments. Although a K concentration of 5.0 me K means a considerable high concentration, the plants of this treatment did not show any depressive effects. Moreover this treatment (5.0 me K) showed the highest yield in beet roots and sugar, which, however, did not differ significantly from the yields of the treatment “1.0 me K”. It is concluded that this K concentration (1.0 me) of the nutrient solution can be regarded as optimal for sugar beet plants. Also under field conditions the order of magnitude of this K concentration in the soil solution may be optimal. 4. The daily uptake rates for K were the higher the K concentration of the nutrient solution was. This tendency was particularly obvious in the beginning of the growing period. In each treatments the highest K uptake rates were observed during the maximum leaf growth (2nd half of July). 5. High K uptake rates resulted mainly in a considerable increase of the K content of the leaves. But the total cation content (K, Na, Mg, Ca) of the leaves was not affected by these high K uptake rates. In the treatment “0.2 me K” the very low K content of the leaves was compensated quantitatively by higher contents of Ca and Mg. This replacement of K by Ca and Mg, however, could not substitute for the specific functions of K in yield formation. 6. The water consumption of the plants related to the weight unit beet roots was the lower the higher the K concentration of the nutrient solution was. Particularly during August and the 1^st half of September simultaneously with a higher production of organic material the better K supply resulted in an absolutely lower water consumption.     

Phytosanitäre Effekte bei der Mineraldüngung von Zuckerrüben

Phytosanitary effects of the fertilization of sugar beet Several examples are given which show that through certain mineral fertilizer applications the resistance of sugar beets to certain pests and pathogens could be increased. In a few cases side effects of mineral salts on the activity of various pests and pathogens could also be observed and explained.     

Überprüfung eines Schätzverfahrens zur Ermittlung von Kennwerten der Wasserbindung anhand der Labordatenbank des Niedersächsischen Bodeninformationssystems

Testing a method for estimating water retention parameters using the laboratory database of the Lower Saxony Soil Information System The validity of the method used for estimating field capacity (pF > 1.8), plant available water (pF 1.8 – 4.2), air capacity (pF < 1.8), and total pore volume from soil texture, packing density (bulk density + 0.009 % clay) and humus content described by the Arbeitsgruppe Bodenkunde (1982) was checked on the basis of 1693 pF curves of the laboratory database of the Lower Saxony Soil Information System (NIBIS). The positive and negative corrections for humus content applied in this method to the above parameters are clearly too small. Use of tables for estimating the pore volume of humus-free soils leads to overestimation. It will only be possible to work out an alternative method applicable to all classes of soils when the database has been extended.     

Pflanzenverfügbarkeit der Phosphatvorräte ackerbaulich genutzter Böden. -Langfristige Feldversuche zur Nutzbarkeit des Bodenphosphors und zur Bewertung der Bodenuntersuchung -

Availability of Phosphate Reserves in Arable Soils - Long Term Field Experiments for Assessing Soil P Reserves and Critical Soil Test Values - The objective of this work is to quantify the plant availability of soil P reserves accumulated by former fertilizer applications, the possibility of utilizing them by arable field crops and to determine critical soil test values. For this purpose several long term field experiments with large plots without replicates were initiated in 1977 on luvisols from loess (pH 6.8 – 7.4) in Lower Saxony with a sugar beet - winter wheat - winter barley/winter wheat crop rotation. Annual P applications were 0, 45, 90, 135 and 180 kg P₂O₅/ha as triple phosphate. Application of other fertilizers and plot management were according to farmer's practice. Despite of high yield levels phosphate response of plants was only 2 % at its maximum in the average of all crops in 15 years. This was confirmed by small plot experiments with four replicates placed into the large plots after 9 years, when soil P levels had been differentiated under the influence of plant P removal and P application. Herewith in agreement, shoot P concentration was found within the range generally regarded sufficient. It is therefore concluded that plant P demand has been fully satisfied by soil P reserves. Soil P test values, monitored by the P(H₂O) method of Sissingh, decreased markedly in 15 years, when no P was applied, they remained approximately constant when P application was equal to P removal and they increased when P addition was higher than P removal. Plants on a site with 4 mg P(H₂O)/L initially had severe P deficiency. Maximum yield was obtained when the soil P level was raised to 11 mg P(H₂O)/L. It is concluded that P reserves, which are often high in German arable soils, can be utilized by field crops and thus be lowered to about 10 mg P(H₂O)/L by reducing or omitting P dressings. For practical purposes it is suggested to restrict P application, if necessary at all, to the sugar beet crop in the rotation because they often respond more than small grain.     

Amino sugars and muramic acid—biomarkers for soil microbial community structure analysis

Characterizing functional and phylogenetic microbial community structure in soil is important for understanding the fate of microbially-derived compounds during the decomposition and turn-over of soil organic matter. This study was conducted to test whether amino sugars and muramic acid are suitable biomarkers to trace bacterial, fungal, and actinomycetal residues in soil. For this aim, we investigated the pattern, amounts, and dynamics of three amino sugars (glucosamine, mannosamine and galactosamine) and muramic acid in the total microbial biomass and selectively cultivated bacteria, fungi, and actinomycetes of five different soils amended with and without glucose. Our results revealed that total amino sugar and muramic acid concentrations in microbial biomass, extracted from soil after chloroform fumigation varied between 1 and 27 mg kg⁻¹ soil. In all soils investigated, glucose addition resulted in a 50-360% increase of these values. In reference to soil microbial biomass-C, the total amino sugar- and muramic acid-C concentrations ranged from 1-71 g C kg⁻¹ biomass-C. After an initial lag phase, the cultivated microbes revealed similar amino sugar concentrations of about 35, 27 and 17 g glucosamine-C kg⁻¹ TOC in bacteria, fungi, and actinomycetes, respectively. Mannosamine and galactosamine concentrations were lower than those for glucosamine. Mannosamine was not found in actinomycete cultures. The highest muramic acid concentrations were found in bacteria, but small amounts were also found in actinomycete cultures. The concentrations of the three amino sugars studied and muramic acid differed significantly between bacteria and the other phylogenetic microbial groups under investigation (fungi and actinomycetes). Comparison between the amino sugar and muramic acid concentrations in soil microbial biomass, extracted after chloroform fumigation, and total concentrations in the soil showed that living microbial biomass contributed negligible amounts to total amino sugar contents in the soil, being at least two orders of magnitude greater in the soils than in the soil inherent microbial biomass. Thus, amino sugars are significantly stabilized in soil.     

Reaktion der Zuckerrübe (Beta vulgaris var. altissima) auf die Kaliumdüngung – ein 20‐jähriger Feldversuch

Response of sugar beet ( Beta vulgaris var. altissima ) to potassium fertilization—a 20‐year field experiment A long‐term fertilizer experiment was performed to develop a K fertilization strategy to achieve highest extractable sugar yields (BZE). Sugar beet was grown in a crop rotation with wheat and barley on an alluvial soil (clayic silt) in Lower Saxony with annual recycling of straw and beet tops, respectively. Since 1983, the treatments were as follows: 1) K fertilization with 0, 29, 58, 87,174, and 524 kg K ha^–1 a^–1 corresponding to 0, 0.5, 1, 1.5, 3, and 9 times the average annual K removal by the marketable products of the crop rotation—since 1995, the two highest treatments (3 and 9 times the removal) received only 174 kg ha^–1 every third year; 2) K fertilization according to the average K removal, given each year (58 kg K ha^–1) or every third year (174 kg ha^–1) to sugar beet; 3) annual K fertilization of 87 kg K ha^–1 (1.5 times the removal) applied in autumn or spring, respectively; 4) annual K fertilization, applied as mineral fertilizer or as organic material (recycling of grain and straw or root and leaves); 5) application of 29 kg NaCl ha^–1 to sugar beet supplemental to a yearly application of 58 kg K ha^–1. Both root yield and soil concentration of lactate‐soluble K increased with K fertilization up to the highest K treatment. The extractable sugar content reached a maximum at a yearly application of 174 kg K ha^–1. Averaged over years, the extractable sugar yield (BZE) increased up to the highest K application. The time of K application (autumn or spring) and the source of K (mineral fertilizer or organic material) had no effect on BZE. An additional fertilization with NaCl increased BZE only slightly in single years. Low‐grade muriate of potash containing 33% K and 3% Na can thus be used. The economically optimal K‐fertilization rate was 174 kg K ha^–1 given once in the crop rotation to sugar beet. A soil K concentration of about 110 mg (kg soil)^–1 (lactate‐extractable K) is sufficient in this soil to achieve a high BZE.     

C- und N-Festlegung in Böden Südostniedersachsens nach Krumenvertiefung

Enrichment of C and N in soils of southeastern Niedersachsen after deepening of top soil In a comprehensive study, the effects of deepening of top soil during the last 20 years on C-organic-and N-total-masses of some selected arable land sites have been analyzed. The sampling sites represent soil groups predominating in southeastern Niedersachsen. In 145 plots of 22 agricultural farms with the rotation sugar beets/winter wheat/winter barley, sugar beets/winter wheat/winter wheat respectively, the actual depth of plow horizon varies from 32 to 38 cm in summer. Organic matter has been analyzed in 125 soils. A C-org.- and N-total-balance sheet has been prepared for the time after deepening of the top soils. In luvisols with a top soil deepening of about 10 cm a period of 15 years has been necessary for aquirement of the C-content before deepening. A C-enrichment up to 15 t/ha was recorded with incorporation of plant residues in the last 15 years. During this period up to 1,5t of N/ha accumulated assuming constant C/N-ratios. For chernosems, a similar rate has been determined. In sandy cambisols, the short period of observation of 10 years and less after top soil deepening did not permit a complete reenrichment with organic matter. The ”?potentially”? possible enrichment with organic C amounts to 14–17 t/ha (= 1,4–1,7 t N). Furthermore, luvisols gave a significant correlation between clay- and C-amounts of non deepened soils. A weak interrelation has also been found between clay content and the enrichment potential of organic matter in these soils.     

免耕秸秆还田和传统耕作方式下东北黑土氨基糖态碳的积累特征

以吉林德惠市中层黑土进行7年田间定位试验的小区土壤为研究对象,对免耕(NT)和传统耕作下(CT)耕层(0～20 cm)氨基糖态碳含量的变化特征进行了分析。结果表明,与传统耕作相比,实施免耕7年后整个耕层土壤中氨基糖态碳含量显著增加(p<0.05),以表层(0～5 cm)增加幅度最大,高达94.7%。说明在研究地区,免耕措施有利于微生物代谢物如细胞壁物质等作为潜在的碳源逐渐积累在土壤中。免耕土壤中不同微生物来源氨基糖态碳的含量均较传统耕作有显著增加,但是变化特征有所不同,其中免耕条件下真菌来源的氨基葡萄糖的积累量较传统耕作高出1倍多,而且氨基葡萄糖与细菌来源的胞壁酸的比值(6.9～7.3)显著高于传统耕作(4.7～5.4),暗示实施免耕秸秆还田7年后土壤中真菌已逐渐转为优势群体,而真菌占优势的农田生态系统具有更大的固碳潜力。     

Spatial analysis of long‐term effects of different tillage practices based on penetration resistance

Measuring penetration resistance (PR) is a common technique for evaluating the effects of field management on soils. This study focuses on the effects of long‐term tillage on the spatial distribution of PR, comparing reduced and conventional tillage (CT) practices. The study site, located in Lower Saxony (Germany), has been subdivided into three plots, with one plot having been managed conventionally, whereas reduced tillage (RT) practices have been applied to the other two. In total, PR was measured at 63 randomly selected points. The PR data were stepwise interpolated using kriging with external drift. Core samples have been taken at 20 additional sites. The results show significant differences in PR between the different tillage practices. Within the conventionally managed plot, PR ranges to 2.3 MPa less in the topsoil than under RT. However, measured saturated hydraulic conductivity and amount of biopores at the depth of 30–35 cm are significantly greater under RT, indicating improved soil properties under RT. Comparisons between the headlands (HL) and the inner field point out the effects of intense field traffic in the HL, where maximum PR values of about 6 MPa have been measured. The spatial prediction of PR values show that long‐term effects of different tillage practices result in clearly structured patterns between CT and RT and the HL. Combining extensive PR measurements and point measurements of additional soil properties supports an adequate interpretation of PR data and can lead to fieldwide derivation of soil functions influenced by field management.     

Effect of contrasting changes in hydrothermic conditions on the N<Subscript>2</Subscript>O emission from forest and tundra soils

The effects of intense moistening and alternating freezing-thawing cycles on the N₂O emission from soils of an oak forest (brown forest soil in Lower Saxony, Germany) and southern tundra (cryozem in the area of Tal’nik Station near the city of Vorkuta) were studied in a model experiment. A sharp rise in the N₂O emission reaching 350–670 μg N/m² per h was recorded during the thawing of the brown forest soil, and the loss of nitrogen initiated by the freezing-thawing cycles comprised 74% of the total N₂O emission during the whole experiment. No significant fluxes of N₂O from the tundra soil were recorded during the experiment.     

Potassium substitution by sodium in sugar beet (Beta vulgaris) nutrition on K‐fixing soils

Alluvial soils with illite and vermiculite clay minerals are highly potassium (K)‐fixing. Such soils have been reported to require a huge amount of K fertilization for optimum plant growth. For halophytic plants such as sugar beet, sodium (Na) can be an alternative to K under such conditions. This study was conducted to investigate the possible substitution of K by Na fertilization with reference to K‐fixing soils. Three soils, i.e., Kleinlinden (subsoil), Giessen (alluvial), and Trebur (alluvial), differing in K‐fixing capacities, were selected, and sugar beet plants were grown in Ahr pots with 15 kg soil pot^–1. Three treatments (no K and Na, K equal to K‐fixing capacity of soil, and Na equivalent to regular K fertilization) were applied. In a second experiment, containers (90 cm × 40 cm × 40 cm) were used with 170 kg Kleinlinden soil each, and one sugar beet plant per container was grown. In both experiments, plants were grown till beet maturity, and beets were analyzed for sucrose concentration and other quality parameters such as α‐amino nitrogen to calculate white‐sugar yield with the New Brunswick formula. The results showed that growth and quality of sugar beet were not affected by Na application, and ultimately there was no decrease in white‐sugar yield. Moreover, the soils with more K‐fixing capacity were more suitable for K substitution by Na. It is concluded that Na can substitute K in sugar beet nutrition to a high degree and soils with high K‐fixing capacity have more potential for this substitution.     

Effect of the introduction of the nitrogen-fixing bacteria <Emphasis Type="Italic">Pseudomonas putida</Emphasis> 23 on the nitrogen balance in soil

The inoculation of red beets with the nitrogen-fixing bacteria Pseudomonas putida 23 increased the activity of the nitrogen fixation in the rhizosphere of the plants grown on meadow soil in the central part of the Oka River floodplain. The yield of the red beets and the uptake by plants of nitrogen from the soil and from the ¹⁵N-labeled nitrogen fertilizer applied on the trial microplot increased significantly. A statistically significant additional fixation of nitrogen from the atmosphere and a positive balance of nitrogen in the soil-plant system without significant changes in the bulk content of the soil nitrogen after the plant growing were found in a greenhouse experiment with the application of P. putida. It can be supposed that the excessive nitrogen determined in this system is related to the incorporation into plants of atmospheric nitrogen fixed in the rhizosphere of the inoculated plants. The application of P. putida 23 makes it possible to decrease the rates of NPK fertilizer by two times without losses in the yield of red beets.     

Effects of irrigation-induced salinity and sodicity on soil microbial activity

The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes β-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP.Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties.