Total Nitrogen Yield Research Articles

Suspended Sediment, C, N, P, and Si Yields from the Mississippi River Basin

The annual loads of C,N,P, silicate, total suspended sediment (mass) and their yields (mass area−1) were estimated for six watersheds of the Mississippi River Basin (MRB) using water quality and water discharge records for 1973 to 1994. The highest load of suspended sediments is from the Missouri watershed (58 mt km2 yr−1), which is also the largest among the six major sub-basins. The Ohio watershed delivers the largest load of water (38%). The Upper Mississippi has the largest total nitrogen load (32%) and yield (1120 kg TN km2 yr−1). The loading of organic carbon, total phosphorus and silicate from the Upper Mississippi and Ohio watersheds are similar and relatively high (range 2.1–2.5, 0.068–0.076, and 0.8–1.1 mt km2 yr−1, respectively). The yields of suspended sediments, total phosphorus, total nitrogen, and silicate from the Lower Mississippi watershed are disproportionately the highest for its area, which is the smallest of all the watersheds and has the weakest monitoring network. The loading from the Red and Arkansas watersheds are of lesser importance than the others for most parameters investigated. The total nitrogen loading to coastal waters increased an additional 150% since the early 1900s, and is now dominated by loads from the Upper Mississippi watershed, rather than the previously dominant Ohio watershed. An analysis of trends for 1973–1994 suggests variability among years, rather than uni-directional change for most variables among 11 key stations. Explanatory relationships were established or confirmed to describe TN and TP loadings in terms of the now largely human-created landscape arising mostly over the last 150 years.

Growth and Nitrogen Fixation and Uptake in Dhaincha/Sorghum Intercropping System Under Saline and Non‐saline Conditions

Two field experiments on dhaincha (Sesbania aculeata Pers.) and sorghum (Sorghum bicolor L.) grown in monocropping and intercropping systems was conducted under non‐saline and saline conditions to evaluate dry matter production, total nitrogen (N) yield, land equivalent ratio (LER), soil N uptake and N2‐fixation using 15N isotope dilution method. The first experiment was conducted under non‐saline conditions, three different combinations of sesbania (ses) and sorghum (sor) were investigated in the intercropping system (2ses:1sor; 1ses:1sor, and 1ses:2sor, row ratio). Whereas, in the second experiment, only one combination (1ses:1sor row ratio) was tested under saline conditions. Results of the first experiment showed that dry matter yield of sole sorghum was higher than that of sole sesbania, and was similar to that produced by the intercropping treatments; however, its total N uptake was the lowest, with no significant differences being found between sole sesbania and intercropping treatments. The LERs in 2ses:1sor and 1ses:2sor treatments were higher than one, reflecting a greater advantage of intercropping system in terms of land use efficiency. In the second experiment, dry matter yield of a sole crop of sesbania was significantly higher than that of a sole sorghum or a mixed treatment. Total N uptake in sesbania grown alone was four times higher than that of sole sorghum; whereas, the mixed cropping was 260% greater that of the sole sorghum. In both experiments, percentages of N2 fixed by the sesbania in the intercropping system were considerably enhanced relative to sole cropping of sesbania. On the other hand, the magnitude of intraspecific competition for soil N uptake was affected by the different arrangement of crops in the mixture, and it was considerably reduced in the 2ses:1sor row ratio. Results on the relative growth of plants on saline soil compared with that on non‐saline soil clearly demonstrated that sesbania was more salt tolerant than the sorghum. Amounts of N2‐fixed by sesbania grown in saline soil were close or even higher than those grown under non‐saline conditions. The use of intercropping systems of legumes and non‐legumes would be a promising agricultural practice for rehabilitation of saline wasted lands, after a careful selection of appropriate tolerant genotypes to the prevailing saline conditions.

GRASS RESPONSE TO CLIPPING IN AN AFRICAN SAVANNA: TESTING THE GRAZING OPTIMIZATION HYPOTHESIS

It has been suggested that grazing could stimulate the aboveground dry mass and/or nitrogen yields available to grazers (i.e., the grazing optimization hypothesis, GOH), but the actual importance of this effect is still controversial. The GOH has only been tested for a few grasslands and one savanna ecosystem, but not for the moistest and warmest grasslands and savannas of the world. The objectives of this study were to test the GOH in the humid savanna of Lamto (West Africa) by analyzing the growth of grasses in response to a field trial with three levels of clipping × two levels of fertilization. We quantified the effects of clipping and fertilization on the dry matter and nitrogen yields to grazers (i.e., mass or nitrogen amount in clipped‐off tissues during the experiment) and on the remaining yield (i.e., mass or nitrogen amount in residual phytomass at the end of the experiment) over a three‐month period. Total phytomass yield, the sum of yield to grazers, and the remaining yield was maintained under moderate clipping frequency and fertilization as compared to control conditions. Both clipping frequencies decreased the remaining phytomass yield as compared to control plots. Clipping frequency significantly increased nitrogen concentrations in the total yield, in the remaining yield, and in the yield to grazers. Total nitrogen yield and nitrogen yield to grazers were 65% and 91% higher on the plots experiencing moderate clipping frequency with fertilization as compared to control plots. The study shows that grazers in this humid savanna system could potentially modify ecosystem processes in such a way as to partly alleviate nutritional deficiencies, but only in the presence of increased nitrogen availability.

Enhanced Soybean Plant Growth Resulting from Coinoculation of Bacillus Strains with Bradyrhizobium japonicum

Nodulation and subsequent nitrogen fixation by soybean [Glycine max (L.) Merr.] plants are inhibited by low root zone temperatures (RZTs). Plant growth promoting bacteria can help overcome these deleterious effects. Three Bacillus strains, B. subtilis NEB4 and NEB5 and B. thuringiensis NEB17, were isolated from inside the nodules of vigorous field‐grown soybean plants in 1998, and were shown to have plant growth promoting activity on pouch‐grown soybean plants under greenhouse conditions. To test their ability to improve soybean nodulation and growth under low RZTs, these strains were coinoculated onto soybean plants, with Bradyrhizobium japonicum, under greenhouse conditions at RZTs of 25, 17, and 15°C, and under field conditions in a short growing season area. In all cases, the experiments were conducted with soybean cultivar OAC Bayfield. All the three Bacillus strains enhanced soybean nodulation and growth in greenhouse and field experiments. Coinoculation with NEB17 provided the largest and most consistent increases in nodule number, nodule weight, shoot weight, root weight, total biomass, total nitrogen, and grain yield. The other two strains provided positive responses in only 1 of the 2 yr of field‐testing. Thus, B. thuringiensis NEB17 would be suitable for use as a plant growth promoting bacterial strain in soybean production systems in short growing season regions.

Natural background concentrations of nutrients in streams and rivers of the conterminous United States.

Determining natural background concentrations of nutrients in watersheds in the developed world has been hampered by a lack of pristine sampling sites covering a range of climatic conditions and basin sizes. Using data from 63 minimally impacted U.S. Geological Survey reference basins, we developed empirical models of the background yield of total nitrogen (TN) and total phosphorus (TP) from small watersheds as functions of annual runoff, basin size, atmospheric nitrogen deposition rate, and region-specific factors. We applied previously estimated in-stream loss rates to yields from the small watershed models to obtain estimates of background TN and TP yield and concentration throughout the stream/river network in 14 ecoregions of the conterminous United States. Background TN concentration varies from less than 0.02 mg L(-1) in the xeric west to more than 0.5 mg L(-1) along the southeastern coastal plain. Background TP concentration varies from less than 0.006 mg L-(1) in the xeric west to more than 0.08 mg L(-1) in the great plains. TN concentrations in U.S. streams and rivers currently exceed natural background levels by a much larger factor (6.4) than do TP concentrations (2.0). Because of local variation in runoff and other factors, the range of background nutrient concentrations is very large within some nutrient ecoregions. It is likely that background concentrations in some streams in these regions exceed proposed nutrient criteria.

Mapping of QTL associated with nitrogen storage and remobilization in barley (Hordeum vulgare L.) leaves.

Nitrogen uptake and metabolism are central for vegetative and reproductive plant growth. This is reflected by the fact that nitrogen can be remobilized and reused within a plant, and this process is crucial for yield in most annual crops. A population of 146 recombinant inbred barley lines (F(8) and F(9) plants, grown in 2000 and 2001), derived from a cross between two varieties differing markedly in grain protein concentration, was used to compare the location of QTL associated with nitrogen uptake, storage and remobilization in flag leaves relative to QTL controlling developmental parameters and grain protein accumulation. Overlaps of support intervals for such QTL were found on several chromosomes, with chromosomes 3 and 6 being especially important. For QTL on these chromosomes, alleles associated with inefficient N remobilization were associated with depressed yield and higher levels of total or soluble organic nitrogen during grain filling and vice versa; therefore, genes directly involved in N recycling or genes regulating N recycling may be located on these chromosomes. Interestingly, the most prominent QTL for grain protein concentration (on chromosome 6) did not co-localize with QTL for nitrogen remobilization. However, QTL peaks for nitrate and soluble organic nitrogen were detected at this locus for plants grown in 2001 (but not in 2000). For these, alleles associated with low grain protein concentration were associated with higher soluble nitrogen levels in leaves during grain filling; therefore, gene(s) found at this locus might influence the nitrogen sink strength of developing barley grains.

Response of field-grown soybean to co-inoculation with the plant growth promoting rhizobacteria Serratia proteamaculans or Serratia liquefaciens, and Bradyrhizobium japonicum pre-incubated with genistein

Plant growth promoting rhizobacteria (PGPR) and genistein have been used separately to improve soybean nodulation, nitrogen fixation and yield. Field experiments were conducted to evaluate the combined effect of PGPR and genistein in 1996 and 1997 in Canada. Genistein was used to pre-incubate Bradyrhizobium japonicum strain 532C. Three factors were tested: two genistein concentrations (0 and 20 μM), two PGPR strains ( Serratia proteamaculans 102 and Serratia liquefaciens 2–68), and two soybean cultivars (‘AC Bravor’ and ‘Maple Glen’). The results indicated that genistein increased nodule number and nodule weight, while the two PGPR strains used affected the measured variables differently. In many cases treatment effects of PGPR were not significant. At maturity, the shoot nitrogen content of ‘AC Bravor’ in 1996, and seed nitrogen content and total nitrogen yield in 1997 were increased by genistein. Soybean yield was increased by genistein in 1997, and was not affected by both genistein and PGPR treatments in 1996. The results indicate that there were no additional improvement in nodulation and nitrogen fixation by using both genistein and these PGPR.

Yield of nitrogen from minimally disturbed watersheds of the United States

Watersheds of the US Geological Survey's Hydrologic Benchmark Network program were used in estimating annual yield of total nitrogen and nitrogen fractions (ammonium, nitrate, dissolved organic N, particulate N) in relation to amount of runoff, elevation, and watershed area. Only watersheds minimally disturbed with respect to the nitrogen cycle were used in the analysis (mostly natural vegetation cover, no point sources of N, atmospheric deposition of inorganic N < 10 kg ha−1 y−1). Statistical analysis of the yields of total nitrogen and nitrogen fractions showed that elevation and watershed area bear no significant relationship to nitrogen yield for these watersheds. The yields of total nitrogen and nitrogen fractions are, however, strongly related to runoff (r2 = 0.91 for total N). Annual yield increases as runoff increases, but at a rate lower than runoff; annual discharge-weighted mean concentrations decline as annual runoff increases. Yields of total nitrogen and most nitrogen fractions bear a relationship to runoff that is nearly indistinguishable from a relationship that was documented previously for minimally disturbed watersheds of the American tropics. Overall, the results suggest strong interlatitudinal convergence of yields and percent fractionation for nitrogen in relation to runoff.

Productivity of four sesbania species on two soil types in Ethiopia

In Ethiopia, lack of quality forage in adequate quantities is a major constraint to livestock productivity. Fast growing N2 fixing Sesbania have shown great promise both as high quality fodder and green manure. The objective of this study was to evaluate and select among the species S. macrantha, S. rostrata, S quadrata and S. sesban for fodder yield, quality and green manure potential. The field experiment was conducted on a light soil (loam, Alfisol) and a heavy soil (cracking type clay, Vertisol) at Debre Zeit (9° N and 39° E, 45 kms SE of Addis Ababa). There were two cutting treatments: cutting once at ground level or cutting twice at 50 cm (first, 65 days after sowing; second, 40 days later). A two-factor factorial in randomized block design was used. S. macrantha performed better on the light soil producing the highest dry matter (DM) yields of leaf (2.8 t/ha), stem (6.3 t/ha) and total nitrogen (151 kg/ha) in 105 days than the rest of the species. Most species performed poorly on the heavy soil. S. quadrata, however, showed better adaptability to the heavy soil (5.5 t/ha DM) than any of the other species. The lowest DM yield was recorded for S. rostrat which could be due to poor nodulation. Cutting twice over the 105 days growth period caused a drastic reduction in DM yield, but resulted in higher leaf-to-stem ratio and total N yield. The nutritional composition of all the species was within an acceptable range for livestock requirements. N content (4%) and IVDMD (over 70%) were high. S. macrantha had superior overall performance and seems promising both as high quality fodder and green manure crop. Under rain-fed conditions, cutting once was better than cutting twice particularly for S. macrantha.

Defoliation‐induced enhancement of total aboveground nitrogen yield of grasses

We conducted an experiment in a northern mixed‐grass prairie at Wind Cave National Park, South Dakota, USA to evaluate the effect of defoliation frequency on aboveground net primary production (ANPP), shoot nitrogen concentration, and aboveground N yield of graminoids. ANPP was significantly reduced at weekly and biweekly defoliation frequencies, but unaffected relative to unclipped controls at monthly and bimonthly frequencies. By contrast, clipping at all frequencies increased shoot N concentration above that of controls, and this increase was greatest at monthly or more frequent defoliations. Total aboveground N yield and potential N yield to grazers were greatest at intermediate (bimonthly to biweekly) frequencies. We suggest that grazers may maximize their nutritional status in this system by periodically regrazing areas at frequencies near the approximately monthly optimum that we observed.

NUTRIENT CONCENTRATIONS AND YIELDS IN UNDEVELOPED STREAM BASINS OF THE UNITED STATES1

ABSTRACT: Data from 85 sites across the United States were used to estimate concentrations and yields of selected nutrients in streams draining relatively undeveloped basins. Flow‐weighted concentrations during 1990–1995 were generally low with median basin concentrations of 0.020, 0.087, 0.26, 0.010, and 0.022 milligrams per liter (mg/L) for ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus, respectively. The flow‐weighted concentration of nitrate exceeded 0.6 mg/L in only three basins. Total nitrogen exceeded 1 mg/L in only four basins, and total phosphorus exceeded 0.1 mg/L in only four basins. The median annual basin yield of ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus was 8.1, 26, 86, 2.8, and 8.5 kilograms per square kilometer, respectively. Concentrations and yields of nitrate tended to be highest in northeastern and mid‐Atlantic coastal states and correlated well with areas of high atmospheric nitrogen deposition. Concentrations and yields of total nitrogen were highest in the southeastern part of the nation and in parts of the upper Midwest. In the northeast, nitrate was generally the predominant form of nitrogen, and in the southeast and parts of the upper Midwest, organic nitrogen was the dominant form. Concentrations of total phosphorus were generally highest in the Rocky Mountain and Central Plain states.

Stimulation of N2‐fixation in chickpea by gamma irradiation as affected by different levels of ammonium sulfate fertilizer

A pot experiment was conducted under natural climatic conditions to study the effect of low doses of gamma irradiation (0, 5, 10, and 20 Gy) on the performance of winter chickpea (Cicer arietinum L.) in the presence of increased supply of 15N labeled ammonium sulfate (0, 20, 50, and 100 kg N ha‐1). Presowing seed irradiation produced a significant increase in dry matter production (up to 3 6%) and total nitrogen yield (up to 45%). The stimulative effect of irradiation was more pronounced with the application of NH4 +‐N fertilizer. Seed irradiation increased the amount of N2‐fixation by 8–61% depending on the dose and level of NH4 +‐N fertilizer rate. A 10 Gy was found to be the optimal irradiation dose for enhancing N2‐fixation. High levels of NH4 +‐N decreased the percentage and the amount of N2‐fixation, but did not affect nodule formation. However, the presowing 10 Gy irradiation dose reduced the negative effect of ammonia‐N fertilizer on N2‐fixation. Therefore, we recommend irradiating chickpea seeds with a 10 Gy dose before planting in soil containing high levels of mineral nitrogen to reduce its negative effect on N2‐fixation.

Water quality of a lowland stream in a New Zealand dairy farming catchment

A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m‐3 in winter, with the bulk comprising nitrate nitrogen (NO‐ 3‐N). During summer NO‐ 3‐N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m‐3, respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m‐3 on several occasions and mean concentrations at the three sites were 0.165–0.272 g m‐3. Faecal coliform and enterococci bacteria concentrations were 64–26000 and 7–23000 cfu per 100 ml, respectively. Specific yields of TN and NO‐ 3‐N (35.3 and 30.7 kg ha yr‐1, respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr‐1, respectively) were more in accord with other studies. Greater use of land treatment of liquid wastes will reduce stream inputs of faecal organisms, NH4‐N and P.

Effect of salt stress on interaction between lentil ( Lens culinaris ) genotypes and Rhizobium spp. strains: symbiotic N 2 fixation in normal and sodic soils

Following screening, selection, characterization and examination of their symbiotic N2 fixation, only two Rhizobium strains (ND-16 and TAL-1860) and four lentil genotypes (DLG-103, LC-50, LC-53 and Sehore 74-3) were found to be suited to sodic soils. Interactions between salt-tolerant lentil genotypes and Rhizobium strains were found to be significant, and resulted in greater nodulation, N2 fixation (nitrogenase activity), total nitrogen, plant height, root length and grain yield in sodic soils under field conditions compared to uninoculated controls. Significantly more nodulation, nitrogenase activity, glutamine synthetase (GS) and NADH-dependent glutamate synthase (NADH-GOGAT) activities were found in normal soil as compared to the soil supplemented with 4% and 8% NaCl. Salt stress inhibited nitrogenase, GS and NADH-GOGAT activities. However, nitrogenase activity in nodules was more sensitive to salt stress than GS and NADH-GOGAT activities (NH4+ assimilation). The relevance of these findings for salt-tolerant symbionts is discussed.

Effect of high pressure homogenization and papain on the preparation of autolysed yeast extract

The effect of high pressure homogenization (600 and 1000 bar) prior to autolysis of a commercial pressed baker's yeast was examined. High pressure homogenization released a maximum of 30% of the solids and 34% of the total nitrogen (TN). After autolysis of the whole homogenized slurry, high yields of solids and TN (up to 81 and 85%, respectively) were obtained. Autolysis of non-homogenized controls yielded much lower yield values (30 and 39%, respectively), whereas autolysis in the presence of papain but without prior disruption gave intermediate values (50 and 61%, respectively). The various treatments led to changes in the extract composition: standard autolysates had the highest total nitrogen and true protein weight contents and the lowest carbohydrate content, whereas this trend was reversed when cells were first disrupted before autolysis. In contrast to controls obtained by standard autolysis without or with papain, centrifuged autolysates from pre-homogenized fractions were not clear. Treatment with a combination of a flocculation and a weighting agent clarified the extracts but resulted in a loss of solids (approximately 20%), including nitrogen and carbohydrates.

THE ROLE OF COMPLEMENTARITY AND COMPETITION IN ECOSYSTEM RESPONSES TO VARIATION IN PLANT DIVERSITY

To investigate how plant diversity affects ecosystem-level processes such as primary production and nutrient cycling, I established an experimental plant diversity gradient in serpentine grassland using four functional groups of plants: early season annual forbs (E), late season annual forbs (L), perennial bunchgrasses (P), and nitrogen fixers (N). These groups differ in growth form, phenology, and other traits relevant to nutrient cycling (e.g., rooting depth, litter C:N ratio). Two or three species of each type were planted in single-group treatments, and in two-, three-, and four-way combinations, giving a range of richness from zero to nine species. I tested the hypothesis that, because of complementary resource use, increasing functional group diversity will lead to higher net primary production. At the scale of this experiment (α-diversity and yearly production), more diverse treatments were not necessarily the most productive. Live plant biomass varied more within than among levels of diversity. In most two-, three-, and four-way mixtures of functional groups, overall productivity did not differ significantly from the average of the yields of component one-group treatments. This pattern apparently resulted from competition: early season annuals and late season annuals reduced the biomass of perennial bunchgrasses (the most productive group in monoculture) below levels expected from monoculture yields. Relative Yield Totals (RYT) indicated complementary resource use in the EL and LP two-way and ELPN four-way mixtures. In the EL mixture, complementarity appeared to result from temporal rather than spatial partitioning of resources. Because of shifts in root:shoot ratio in mixtures, however, only the LP treatment had consistently significant RYT >1 when assessing total (roots plus shoots) productivity and nitrogen yield. These results show that (1) composition (the identity of the species present) can be at least as important as richness (the number of species present) in effects on ecosystem processes; (2) competition during critical parts of the growing season may prevent absolute increases in net primary production with increasing diversity, despite complementary resource use at other times of the year; and (3) shifts in belowground allocation in species mixtures can have significant effects on estimates of productivity and resource use as species diversity changes.

Plant growth promoting rhizobacteria accelerate nodulation and increase nitrogen fixation activity by field grown soybean [Glycine max (L.) Merr.] under short season conditions

A 3 × 2 × 2 factorial field experiment, organized in a randomized complete block split-plot with four replications, was conducted in 1994 to evaluate the effect of two plant growth-promoting rhizobacteria (PGPR) strains (Serratia liquefaciens 2-68 or Serratia proteamaculans 1-102) on nodulation, nitrogen fixation, and total nitrogen yield by two soybean cultivars in a short season area. The experiments were conducted at the Emile A. Lods Research Centre, McGill University, Macdonald Campus, Montreal, Canada, and performed at two adjacent sites. One site was fumigated with methyl bromide (50 g m-2). Another site was kept unfumigated. Co-inoculation of soybean with B. japonicum and PGPR increased soybean nodulation and hastened the onset of nitrogen fixation, when the soils were still cool. Total fixed N, fixed N as a percentage of total plant N, and protein and N yield were also increased by PGPR inoculation. AC Bravor tended to be more responsive to both PGPR treatments for total fixed N and N yields than Maple Glen, suggesting that inoculation with PGPR was more effective for cultivars with higher yield potentials.

Regional interpretation of water‐quality monitoring data

We describe a method for using spatially referenced regressions of contaminant transport on watershed attributes (SPARROW) in regional water‐quality assessment. The method is designed to reduce the problems of data interpretation caused by sparse sampling, network bias, and basin heterogeneity. The regression equation relates measured transport rates in streams to spatially referenced descriptors of pollution sources and land‐surface and stream‐channel characteristics. Regression models of total phosphorus (TP) and total nitrogen (TN) transport are constructed for a region defined as the nontidal conterminous United States. Observed TN and TP transport rates are derived from water‐quality records for 414 stations in the National Stream Quality Accounting Network. Nutrient sources identified in the equations include point sources, applied fertilizer, livestock waste, nonagricultural land, and atmospheric deposition (TN only). Surface characteristics found to be significant predictors of land‐water delivery include soil permeability, stream density, and temperature (TN only). Estimated instream decay coefficients for the two contaminants decrease monotonically with increasing stream size. TP transport is found to be significantly reduced by reservoir retention. Spatial referencing of basin attributes in relation to the stream channel network greatly increases their statistical significance and model accuracy. The method is used to estimate the proportion of watersheds in the conterminous United States (i.e., hydrologic cataloging units) with outflow TP concentrations less than the criterion of 0.1 mg/L, and to classify cataloging units according to local TN yield (kg/km2/yr).

Nitrogen Content, Oil Content and Oil Composition of Oat Cultivars (A. sativa) and WildAvenaSpecies in Relation to Nitrogen Fertility, Yield and Partitioning of Assimilates

Abstract Three European and three North American oat cultivars (Avena sativa) and 10 wildAvenaspecies were grown to maturity in pots at three nitrogen fertility levels. The yield and nitrogen content of plant parts, and the production and partitioning of dry matter and nitrogen were measured. Groats were also analysed for oil content and composition. Some wild species had high groat oil (12–13%). Groat nitrogen was higher in wild species (2·9–6·3%) than cultivars (1·5–2·7%). Increases in total yield and total nitrogen yield closely corresponded with increases in nitrogen fertility level. Two wild species, with groat nitrogen contents significantly greater than those of all the cultivars at all fertility levels (A. maroccana,A. canariensis), also had total plant dry matter yields and total plant nitrogen yields that were not significantly different from those of a number of cultivars. The hull contributed substantially to dry matter and nitrogen yield in some wild species, and in two (A. canariensis,A. maroccana) partitioning of both dry matter and nitrogen to the grain was not significantly different from those for most cultivars. There were significant genotype×fertility interactions for a number of characteristics, but there was no evidence that wild species had superior nitrogen economies at any fertility level. In a comparison of cultivars, however, variation in groat nitrogen content was associated with variation in nitrogen partitioning.

Yield and quality components of silage maize in killed and live cover crop sods

In sloping areas with high precipitation, planting maize into live winter cover crop sods may help to alleviate the environmental problems associated with clean-tillage production systems of maize. The present study evaluates the performance of silage maize ( Zea mays L.) under several cultivation methods: CC (conventional cropping system, i.e., maize was sown into the bare, autumn-ploughed soil); LGS/CK (maize was planted into a living Italian ryegrass ( Lolium multiflorum Lam.) sod which was subsequently herbicidally killed); and LGS/MR (similar to LGS/CK, but the ryegrass was mechanically regulated). The research was conducted in the midlands of Switzerland on a fertile sandy loam under humid conditions during three cropping seasons. With 110 kg N ha −1 (fertilizer nitrogen plus mineral nitrogen of the soil at maize planting), the CC system was much more productive than were the LGS/CK and LGS/MR systems in terms of dry matter and nitrogen yields of maize. Increasing the nitrogen supply to 250 kg N ha −1 considerably reduced the yield advantage of CC over the LGS/CK and LGS/MR systems, indicating that nitrogen was the most limiting factor for maize yield in the mulch seeding systems. With 250 kg N ha −1, the LGS/CK and LGS/MR systems produced greater total yields of digestible organic matter (maize plus ryegrass) than did the CC system, whereas the total nitrogen yield was similar for all cropping systems. The whole-shoot concentrations of nitrogen were highest under CC, irrespective of the level of nitrogen supply. With 110 kg N ha −1, concentrations of phosphorus and magnesium were clearly higher for the mulch seeding systems. There were only minor differences among the cropping methods in the concentrations of potassium and calcium in the whole shoot. When 250 kg N ha −1 were applied, there were no significant variations among the cropping systems in the concentrations of minerals. Changes in the botanical composition of the cover crop sod and in the time and method of cover crop control may help to reduce the competition for nitrogen between maize and the living mulch.