Nitrogen-deficient Soils Research Articles

3D chemical map and a theoretical life model for Neuropteris ovata var. simonii (index fossil, Asturian, Late Pennsylvanian, Canada)

The largest known 65-cm frond segment of Neuropteris ovata var. simonii (Order: Medullosales) from the Late Pennsylvanian of Sydney Coalfield, Canada, is preserved as compression and naturally macerated cuticle and comprises the study sample. The study objectives included (i) analyzing the chemical variability throughout the frond, (ii) interpreting chemical differences in the lower from the upper part of the frond (impossible to do from fragmented specimens), (iii) inferring the likely biopolymeric make-up of the tissues of the once-living plant, (iv) estimating the likely metabolic cost of plant tissue production, and (v) suggesting autecological aspects.The chemical variables (functional groups), obtained by Fourier transform infrared (FTIR) spectroscopy, are interpreted by principal component analysis (PCA) where three PCs explain 89.9% cumulative variance. In effect, this chemometric analysis of functional groups, which is named the 3D chemical map, constitutes a first-time study of a three-dimensional component space in medullosalean frond architecture.The 3D chemical map revealed new insights into relative contributions and distributions of aliphatic, aromatic, and oxygen-containing functional groups from which minimal diagenetic alteration was inferred. The proposed life model for the Sydney ovata plant is summarized as follows: (i) continuous variations of functional-group ratios from lower to upper frond parts are reflective of the continuous variation of foliar morphology (including the corresponding plant tissues), and thus frond architecture (ii) compounds likely related to tannins, lignins, and resins are proposed as the tissue biopolymers of the once-living frond, and (iii) comparison of average bond energy data of the functional groups allowed insights into the metabolic cost of tissue production, where the robust and stiffer lower part of the frond was metabolically more expensive than the slender and more flexible upper part. Inferred is that tannins, and resins were also factors in the chemical defenses against herbivory, and that the ovata plant was an opportunistic colonizer of flood-disturbed sites likely characterized by nitrogen-deficient soils and full-sun conditions.Generalization extending to the ovata species (population) is hypothesized.The use and results of the 3D chemical map introduced a paradigmatic shift into Carboniferous plant studies with profound implications for circumscribing more realistically species and their reconstructions of whole-plants as well as their autecology and synecology.

A substrate-based approach for the selection of oil-bearing heterotrophs from nitrogen-deficient soil for lipid production.

In this study, nine heterotrophic yeast isolates were tested for their ability to assimilate crude glycerol and consecutive conversion to triacylglycerides (TGAs). All the organisms were initially screened on crude glycerol-based selection media, and those producing lipid globules were further evaluated for lipid production. Sudan Black B staining of eight isolates showed lipid globules. These strains were further studied at different C/N ratio. The molecular identification revealed that the isolates belonged to the genera of Yarrowia and Candida. Among these isolates, SKY7 (Yarrowia lipolytica) produced up to 42.04 ± 0.11 % of lipid w/w) with a C/N ratio of 100 and fermentation time of 72 h. The other strains produced 5.82 ± 0.4 to 34.57 ± 0.44 % lipid (w/w). The GC-flame ionization detector (FID) lipid profile showed that the lipid produced by the strains had close resemblance with vegetable oil and could serve as a feedstock for biodiesel production. Biolog test of the isolates revealed a wide spectrum of carbon utilization.

INTERCROPPING EFFICIENCY AND ITS EFFECTS ON SOIL FAUNA POPULATIONS IN EGYPT

Intercropping of non-legume plant with a legume crop is proving a successful system for better use of nutrients by plants, particularly in nitrogen deficient soils. Such a system may affect soil fauna activity. The present experiment was conducted at Fayoum Governorate (Egypt) in order to study the impact of wheat intercropped with faba bean on soil fauna populations. Cultivation period was between November 2010 and April 2011. Five treatments were designed: (1) wheat alone, (2) faba bean alone, (3) wheat intercropped with faba bean (1:1), (4) wheat intercropped with faba bean (2:1), and (5) wheat intercropped with faba bean (1:2). Soil fauna were collected monthly during the cultivation period by means of the pitfall trap method. Data of soil fauna populations were statistically treated by advanced multivariate statistical methods, correspondence analysis and ascending hierarchic classification. Soil fauna were dominated by Collembola, spiders, Diptera, Aphididae, Formicidae, Orthoptera and Coleoptera. Generally, intercropping increased soil fauna populations. This increase was associated with wheat intercropped with more rows of faba bean. These populations were also increased as the age of plants increased. The percentages of trophic groups including: herbivores, carnivores and detritivores were also discussed.

Effect of competition from a C4 grass on the phosphorus response of a subtropical legume

Tropical pasture systems are typically dominated by C4 grasses growing on nitrogen (N) deficient soils. Under these conditions, N2-fixing legumes should have a competitive advantage, yet low legume contents are often reported in these systems. This work investigates whether below-ground competition for phosphorus (P) is limiting the ability of legumes to compete in swards of C4 grasses when grown in a sand matrix. The external P requirement of a subtropical legume (butterfly pea, Clitoria ternatea L.) and a C4 grass (buffel grass, Cenchrus ciliaris L.) were initially determined in a P-response experiment. Four rates of P (4.6–78.2 mg P kg–1 of Colwell P) were subsequently selected to investigate the growth response of the butterfly pea when grown with and without competition from a sward of N-deficient buffel grass. Shoot dry matter was determined over successive cuts and P uptake determined at the final harvest at 72 days. Buffel grass dominated the mixed swards and reduced the shoot dry matter production of the butterfly pea by >50% relative to the pure swards. A significant difference in the soil P response curve and shoot P uptake of butterfly pea was not detected between pure swards and those with competition from buffel grass. The ability of C4 grasses to acquire and convert resources (i.e. light, water and nutrients) more efficiently into shoot dry matter is likely to be a major factor resulting in grass-dominated pastures in tropical systems.

Evidence that northern pioneering pines with tuberculate mycorrhizae are unaffected by varying soil nitrogen levels.

Tuberculate mycorrhizae on Pinus contorta (lodgepole pine) have previously been shown to reduce acetylene, but an outstanding question has been to what degree these structures could meet the nitrogen requirements of the tree. We compared the growth, tissue nitrogen contents, and stable nitrogen isotope ratios of P. contorta growing in gravel pits to the same species growing on adjacent intact soil. Trees growing in severely nitrogen deficient gravel pits had virtually identical growth rates and tissue nitrogen contents to those growing on intact soil that had nitrogen levels typical for the area. δ15N values for trees in the gravel pits were substantially lower than δ15N values for trees on intact soil, and isotope ratios in vegetation were lower than the isotope ratios of the soil. The form of soil nitrogen in the gravel pits was almost exclusively nitrate, while ammonium predominated in the intact soil. Discrimination against 15N during plant uptake of soil nitrate in the highly N-deficient soil should be weak or nonexistent. Therefore, the low δ15N in the gravel pit trees suggests that trees growing in gravel pits were using another nitrogen source in addition to the soil. Precipitation-borne nitrogen in the study area is extremely low. In conjunction with our other work, these findings strongly suggests that P. contorta and its microbial symbionts or associates fix nitrogen in sufficient amounts to sustain vigorous tree growth on the most nitrogen-deficient soils.

Survival of Pseudomonas extremorientalis TSAU20 and P. chlororaphis TSAU13 in the rhizosphere of common bean (Phaseolus vulgaris) under saline conditions

The abilities of Pseudomonas extremorientalis TSAU20 and P. chlororaphis TSAU13 to colonise and survive in the rhizosphere of common bean under saline conditions were studied. Four salinity levels (5.0, 7.5, 10.0, and 12.5 dS/m) were maintained in the gnotobiotic system using NaCl salt. Results showed that with increasing salt content root-tip colonization of both bacterial strains was reduced. Both bacterial treatments used in the study increased root and/or shoot length compared to non-treated plants at each NaCl concentration tested, whereas shoot growth was not stimulated at high saline condition (12.5 dS/m). In conclusion, the results of this study indicated that P. extremorientalis TSAU20 and P. chlororaphis TSAU 13 have the ability to survive in ecologically stressed conditions, such as saline and nitrogen deficient soils, and may positively effect on plant growth of bean. High salinity inhibited their colonisation in the rhizosphere of bean and thus their stimulatory effect on plants was also reduced.

Rhizobium gallicum as an efficient symbiont for bean cultivation

Rhizobia are soil bacteria that fix atmospheric nitrogen in symbiosis with legumes in specialized organs called nodules. The legumes thus acquire the autonomy to grow in nitrogen-deficient soils. When nitrogen fixation by indigenous rhizobia is limited, field inoculation with efficient and competitive strains is an economically feasible way to increase production. When the inoculant is made from native strains of rhizobia the success of inoculation should be increased, since local strains are better adapted than commercial inoculants. Here, a Rhizobium gallicum strain, 8a3, previously selected for its competitiveness and symbiotic effectiveness with common bean under laboratory conditions, was tested in field trials in Tunisia. The experiments were conducted in six fields using three common bean cultivars. The majority of the fields showed a low density of the native rhizobia and inefficient nodulation by Sinorhizobium meliloti, a known symbiont of Medicago. Our results show that inoculation with R. gallicum strain 8a3 induced an increase in nodule numbers accompanied by a more than twofold increase in shoot dry yield. Monitoring of the nodulation occupancy through the fingerprinting of the repetitive extragenic palindromic sequences (REP-PCR) showed that strain 8a3 was competitive even in the soil showing a high population density of indigenous R. gallicum, and occupied more than 40% of the nodules. Moreover, in vitro antibiosis assays indicated that strain 8a3 produces antimicrobial activity on agar medium against indigenous common bean rhizobia, including the inefficient strains of S. meliloti. These results point out the benefits that could be achieved by selecting efficient and competitive strains among natural populations of rhizobia.

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon–nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

The Use of Bradyrhizobium to Enhance Growth and Yield of Soybean in Calcareous Soil in Uzbekistan

In this work the effect of inoculation with Bradyrhizobium japonicum S2492 on soybean (Glycine max (L) Merr) growth, nodulation and yield in nitrogen-deficient soil of Uzbekistan was studied. The field experiments were carried out in Tashkent Province of Uzbekistan in a randomized complete block design with four replicates of each treatment. The results revealed positive effects on growth, nodule number and yields of soybean after inoculation with B. japonicum S2492. The yield of soybean varieties was 48% higher for inoculated than for uninoculated plants. The effect of the inoculation was specific for variety but not for growth type. The protein and oil contents of seeds also increased after inoculation. It was concluded that B. japonicum S2492 can be considered as a biofertilizer for increasing the productivity of soybean in nitrogen-deficient soils in Uzbekistan.

Effects of Rates of Inorganic and Organic Fertilisers on Desmodium uncinatum Nodulation, Dry Matter and Seed Yields on Phosphorus and Nitrogen Deficient Soils

Forage legumes are important in the smallholder farming system since they increase the quality of livestock feeds and soil fertility through quality manure. The legumes can also concurrently enhance soil fertility through nitrogen fixation for companion grasses and subsequent cereal crops. Farmers in Kenya are aware of the importance of forage legumes but stunted/slow growth during the establishment year and non availability of low cost seed has limited adoption of this technology. Two experiments were carried out on nitrogen and phosphorus-deficient soils at the National Agricultural Research Centre Kitale. In experiment 1 the effects of nitrogen applied at the rates of 0, 10, 20, 40, 60, 80 and 100 kg N/ha were evaluated for nodulation and dry matter accumulation of Desmodium uncinatum. Experiment 2 evaluated the effects of 0, 23, 46, 69, 92, 115 kg P2O5/ha in the form of single superphosphate fertiliser and 10, 20, 30 and 40 t/ha of farm yard manure on nodulation, herbage dry matter and seed yields of Desmodium uncinatum. A randomized complete block design with 3 replicates was used in each experiment. Nitrogen fertilisers did not increase nodulation and dry matter yields significantly. Increasing nitrogen fertiliser rates beyond 20 kg N/ha resulted in a significant (P<0.01) decline in the total and number of effective nodules produced per plant. Herbage dry matter yields also significantly (P<0.01) declined with application of more than 40 kg N/ha. Application of 23 and 46 kg P2O5/ha significantly (P<0.05) increased nodulation (total and effective number of nodules) and herbage dry matter yields. However, for 2 years there was no advantage in applying rates exceeding 46 P2O5/ha. Farm yard manure also significantly (P<0.5) increased nodulation but there were no significant differences between application of 10 t/ha and higher rates of 20, 30 or 40 t/ha. Herbage dry matter yields were increased by application of farm yard manure though the results were not significant at P>0.05. Seed yields were not significantly increased by phosphate or farmyard manure application.

Growth and Wood Properties of Sitka Spruce (Picea sitchensis (Bong.) Carr.) in Nursing Mixtures Established on Nitrogen-deficient Mineral Soils

Rate of growth and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) were investigated in triplet mixtures with lodgepole pine (Pinus contorta Loud.) (Alaskan provenance) and Japanese larch (Larix kaempferi (Lamb.) Carr.), established on nitrogen-deficient, iron pan soils. These ?nursing? mixtures were compared with pure stands of Sitka spruce that had been either regularly or periodically fertilized with nitrogen. Japanese larch promoted a growth rate in Sitka spruce greater than that achieved in the lodgepole pine-nursed spruce and equivalent to the two pure spruce treatments over the duration of the experiment (current age 28 yrs). Growth of regularly fertilized pure Sitka spruce was not significantly greater than that of periodically fertilized pure spruce. Alaskan lodgepole pine controlled branch size on the lower part of the spruce stems more effectively than the other treatments, although this may have been a function of tree size. Branch characteristics of Japanese larch-nursed spruce, however, were similar to those of the pure spruce treatments. Japanese larch caused an imbalance in crown development in the spruce, although it is unclear from the present study whether this will have an influence on stem and wood quality by the end of the rotation. Overall, the evidence from this study suggests that Japanese larch is an effective nurse of Sitka spruce on nitrogen-deficient iron pans, maintaining a rate of growth similar to that of pure Sitka spruce periodically fertilized with nitrogen and higher than that observed in spruce nursed by Alaskan lodgepole pine.

The Association of Free-Living Nitrogen-Fixing Bacteria with the Roots of High Arctic Graminoids

Samples of graminoid roots and adjacent soil collected from tundra and semidesert sites in the Canadian High Arctic were introduced to a nitrogen-free, nutrient medium formulated to culture N2-fixing microorganisms. Some enrichment cultures of root and soil material showed acetylene reduction activity, suggesting the presence of N2-fixing microorganisms. These microorganisms were found to be associated with the roots of 10 graminoid species (six grasses, two sedges, two rushes). Bacteria isolated from enrichment cultures included members of the genera Clostridium, Desulfovibrio, Klebsiella, and Azospirillum. Neither nitrogenase activity nor the presence of N2-fixing microorganisms was detected in soil or root enrichments of early-season (early July) samples; however, these were observed in enrichments of samples collected late in the growing season (late July to early August). The occurrence of Azospirillum species in arctic soils has not been previously reported, nor has the association of high arctic plants with free-living N2fixing bacteria. The implications of rhizospheric interactions between N2-fixing bacteria and arctic plants which grow in nitrogen-deficient soils are discussed.

Carbon discrimination, water-use efficiency, nitrogen and phosphorus nutrition of the host / mistletoe pair Eucalyptus behriana F. Muell and Amyema miquelii (Lehm. ex Miq.) Tiegh. at permanently low plant water status in the field

Under conditions where both plants had permanently low water status, the mistletoe, Amyema miquelii (Lehm. ex Miq.) Tiegh., had lower nitrogen contents in leaf tissue than its host, Eucalyptus behriana F. Muell. The parasite transpired less than its host which is consistent with the hypothesis that mistletoe transpiration acts as a nitrogen gathering mechanism. Nitrogen and phosphorus contents were generally low in both plants; they were positively correlated, and mistletoes reduced nutrient contents of infested hosts. The carbon discrimination ratio, δ13C (a measure of water-use efficiency) of each plant was within the range reported for other mistletoes and their hosts. Although it did not differ significantly between host and parasite it indicated lower water-use efficiency in the mistletoe. For the nitrogen content of host leaves the gradient within the pair, Δ(δ13C), is much lower compared to the correlation given by Ehleringer et al. (1985). It is concluded that at permanently low water status on nitrogen and phosphorus deficient soils a water-saving strategy accompanied with slow growth is more appropriate for both mistletoe and host.

Biological nitrogen fixation in trees in agro-ecosystems

The integration of trees, especially nitrogen fixing trees (NFTs), into agroforestry and silvo-pastoral systems can make a major contribution to sustainable agriculture by restoring and maintaining soil fertility, and in combating erosion and desertification as well as providing fuelwood. The particular advantage of NFTs is their biological nitrogen fixation (BNF), their ability to establish in nitrogen-deficient soils and the benefits of the nitrogen fixed (and extra organic matter) to succeeding or associated crops.

Relationship Between Soil Nitrogen and Floristic Variation in Late Snow Areas of the Koscinsko Alpine Region [Australia

We studied soil and vegetation patterns of two late snow areas in the Kosciusko alpine region of New South Wales, Australia. Marked floristic differences were found between the lower, central and upper regions of each area. The distributions of six selected species, and the spatial variation in total vegetation cover, were related to the spatial variation in total and exchangeable soil nitrogen concentrations. To test whether variations in soil nitrogen were controlling the spatial separation of late snow area plant species six selected species were subsequently grown at 12-15°C, over a range of increasing nitrogen concentrations. Five of the six selected species (Luzula oldfieldii subsp. dura, Epilobium tasmanicum, Plantago glacialis, Luzula acutifolia subsp. nana and Ranunculus niphophilus) showed similar responses to increasing nitrogen levels, both in terms of relative dry weight production and shoot nitrogen concentrations. Only in one species (Colobanthus nivicola) did responses suggest that it may have been more suited to growth on nitrogen-deficient soils. We concluded, however, that variations in nitrogen availability alone are not responsible for the floristic variation in late snow areas. Possible factors responsible for the variation in floristic composition of the late snow areas are discussed.

Effect of nitrogen supply on rhizosphere interactions and take-all disease of wheat

The effect of NH4NO3 on the expression of take-all in wheat and on the ability of fluorescent pseudomonad bacteria to decrease the growth of the pathogen and the symptoms of the disease was examined in a nitrogen-deficient acidic soil from Western Australia. Application of NH4NO3 increased the fresh weight of shoots, decreased root weight and length, and offset some of the deleterious effects of infection. Inoculation with Gaeumannomyces graminis var. triciti reduced shoot weight and root weight and length at all but the highest level of applied nitrogen. Fluorescent pseudomonads applied to wheat seed (at approximately 108 colony-forming units/seed) reduced seed germination and failed to reduce the severity of take-all expressed as weight or length of shoots or N content. Although the density of black runner hyphae of G. graminis var. triciti was reduced at 40 days and the proportion of root colonized by the pathogen was lower at 28 days with bacterization under severe nitrogen deficiency, no effect of the bacteria was observed if N was added. Key words: Gaeumannomyces graminis var. triciti, fluorescent pseudomonads, wheat, nitrogen.

Nitrate and Ammonium Uptake Kinetics of Three Annual Range Species

AbstractThe uptake kinetics of nitrate and ammonium ions was compared for the annual range species: subclover (Trifolium subterraneum L.), soft chess (Bromus mollis L.), and broadleaved filaree (Erodium botrys [Cav.] Bertol.) to study competitive interactions in nitrogen deficient soils. Fifteen‐day‐old seedlings were allowed to deplete solutions of nitrate or ammonium in the range of 5 to 500 μM concentrations for a 10‐hour period during which net uptake (depletion) was monitored by a sensitive conductance technique. Subclover uptake rates were markedly less than those for soft chess and filaree for both nitrate and ammonium at both low and high concentrations. The evidence supports the hypothesis that subclover is a poor competitor for soil N in part because of this physiological difference.

Glycine-Glomus-Rhizobium Symbiosis

Soybean (Glycine max [L.] Merr. cv Hobbit) plants were grown in a growth chamber for 56 days in a phosphorus- and nitrogen-deficient soil and were colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd) Gerd. and Trappe and Rhizobium japonicum strain USDA 136, or by either organism alone, or by neither. Non-VAM plants received supplemental phosphorus and nonnodulated plants supplemental nitrogen to achieve the same rate of growth in all treatments. Plants of all four treatments had the same (P > 0.05) dry weights at harvest, but VAM plants had higher rates of CO(2) exchange (CER, P < 0.05) and lower leaf P concentrations (P < 0.01). Leaf nitrogen concentrations were lower in nodulated than in nitrogen-supplemented plants (P < 0.01) while starch concentrations were higher (P < 0.01). There was a significant negative relationship between nitrogen and starch (r = -0.989). Statistical evaluation of the data showed that some parameters (CER, leaf area and phosphorus content) were associated with phosphorus nutrition (or the presence of the VAM fungus), others (leaf fresh weight and root dry weight) with nitrogen nutrition (or the presence of Rhizobium), and some (leaf nitrogen and starch content) by both factors. The development of microsymbiont structures and nodule activity were significantly lower in the tripartite association than in plants colonized by one endophyte only. The findings suggest that endophyte effects go beyond those of simple nutrition and associated source-sink relationships.

Growth responses of selected clones of birch (Betula pendula roth.,B. pubescens Ehrh.) and willow (Salix caprea L.,S. cinerea L.) to nitrogen in solution culture

Growth of selected clones of birch and willow obtained from nitrogen deficient soils was compared with that of unselected controls in pot experiments using three levels of nitrogen. Unselected controls of both genera continued shoot growth, albeit very slowly, with a very low level of nitrogen (5 ppm), while selected clones of birch grew significantly more than the controls. Selected clones of willow, on the other hand, ceased shoot growth after 10 weeks with this low nitrogen treatment. Nevertheless, they remained healthy, their leaves containing similar concentrations of nitrogen to those of the plants which continued stem growth throughout the experiment. Furthermore, they had very high root: shoot ratios compared with those of control willows and both selected and unselected birch. The two genera may have developed different mechanisms for tolerating low nitrogen, birch producing a small, relatively efficient root system; willow a larger but less efficient one. Both appear equally effective in ensuring survival on low-nitrogen sites in the field since all the selected clones were obtained from such sites and have survived well in field trials on similar sites.

Effects of nitrogen application before sowing, compared with effects of split applications before and after sowing, for irrigated wheat on the Darling Downs.

On a nitrogen (N) deficient soil on the Darling Downs, yield of irrigated wheat was increased by the application of N as anhydrous ammonia at rates up to 150 kg/ha before sowing. Nitrogen applied at 150 kg/ha before sowing did not increase grain protein concentrations, 300 or 400 kg/ha of N being needed. Nitrogen applications before sowing and during tillering were usually more effective in promoting yield than dressings applied after tillering or applied as several suboptimal dressings between tillering and flowering. Tillering was enhanced by N applied either before sowing or during tillering, whereas application after tillering increased grain size and protein concentration in the grain. Split applications involving equal quantities of N applied to soil before sowing as anhydrous ammonia and to the foliage at tillering as urea solution produced similar grain yields as when the same amount of N was applied before sowing as anhydrous ammonia. Similarly split applications, when equal quantities of N were applied before sowing and after sowing at tillering and boot, were as productive as where all the N was applied before sowing. All urea foliar sprays caused leaf burning, which became evident the day after application. Split N applications were as effective as one application before sowing in increasing the quantity of N contained in grain and generally more effective in increasing the quantity of N in straw. Splitting the N application invariably increased grain protein concentration, and this would seem its chief advantage for irrigated wheat over applying all the N before sowing.