Mineral nitrogen dynamics in irrigated rice–wheat system under different irrigation and establishment methods and residue levels in arid drylands of Central Asia

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to develop and adopt resource conservation technologies. Nitrogen (N) is the key nutrient for crop production in rice–wheat cropping systems in this region. Nitrogen dynamics of dry seeded rice-(aerobic, anaerobic) planted in rotation with wheat (well drained, aerobic) can differ greatly from those of conventional rice cultivation. Soil mineral N dynamics in flood irrigated rice has extensively been studied and understood, however, the impact of establishment method and residue levels on this dynamics remains unknown. Experiments on resource conservation technologies were conducted between 2008 and 2009 to assess the impact of two establishment methods (beds and flats) in combination with three (R0, R50 and R100) residue levels and two irrigation modes (alternate wet and dry (AWD) irrigation (all zero till), and a continuously flooded conventional tillage (dry tillage)) with water seeded rice (WSR) on the mineral N dynamics under dry seeded rice (DSR)-surface seeded wheat systems. N balance from the top 80 cm soil layers indicated that 32–70% (122–236 kg ha⁻¹) mineral N was unaccounted (lost) during rice cropping. The amount of unaccounted mineral N was affected by the irrigation method. Residue retention increased (p < 0.001) the unaccounted mineral N content by 38%. With AWD irrigation, the N loss was not different among dry seeded rice in flat (DSRF), dry seeded rice in bed (DSRB), and conventional tillage WSR. Under different irrigation, establishment methods and residue levels, unaccounted mineral N was mainly affected by plant N uptake and soil mineral N content. Major amounts (43–58%) of unaccounted mineral N from DSR field occurred between seeding and panicle initiation (PI). During the entire rice and wheat growing seasons, NH₄N consistently remained at very high levels, while, NO₃N remained at very low levels in all treatments. In rice, the irrigation method affected NH₄N content. Effect of residue retention and establishment methods were not significant on NH₄N and NO₃N dynamics in both crops and years. Further evidence of the continuously fluctuating water filled pore spaces (WFPS) of 64% and the microbial aerobic activity of 93% at the top 10 cm soil surface during rice growing season indicates soil in the DSR treatments was under frequent aerobic–anaerobic transformation, a conditions very conducive for higher amounts of N loss. In DSR treatments, the losses appeared to be caused by a combination of denitrification, leaching and N immobilization. When intending to use a DSR management strategies need to be developed for appropriate N management, irrigation scheduling, and residue use to increase mineral N availability and uptake before this practices can be recommended.     

The role of active oxygen metabolism in hydrogen peroxide-induced pericarp browning of harvested longan fruit

Effects of hydrogen peroxide (H₂O₂), as exogenous reactive oxygen, on browning and active oxygen metabolism in pericarp of harvested ‘Fuyan’ longan fruit were investigated. The results showed that as compared with the control fruit, there was a higher browning index in pericarp of H₂O₂-treated fruit. The fruit treated with H₂O₂ resulted in increased rate of superoxide anion (O₂⁻) production, reduced activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), decreased amounts of ascorbic acid (AsA), glutathione (GSH) and carotenoid, and increased malondialdehyde (MDA) content. These results indicated that H₂O₂-induced browning in pericarp of harvested longan fruit might be due to a reducing capacity of active oxygen scavenging and an increase of accumulation of O₂⁻, which might stimulate membrane lipid peroxidation, disrupt cellular membrane structure, and cause the loss of cellular compartmentalization, in turn, resulting in the contact of polyphenol oxidase (PPO) and peroxidase (POD) with phenolic substrates and subsequently oxidation phenolics to form brown polymers.     

Influence of UV-C treatment on antioxidant capacity,antioxidant enzyme activity and texture of postharvest shiitake (Lentinus edodes) mushrooms during storage

Shiitake (Lentinus edodes) mushrooms were exposed to UV-C light (4 kJ/m²) and stored in modified atmosphere packaging (MAP) prior to 15 days at 1 ± 1 °C and 95% relative humidity plus 3 days at 20 °C. Mushroom firmness, total phenolics, total flavonoids, ascorbic acid and H₂O₂ contents, superoxide anion (O₂⁻) production rate and activities of catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) were measured. UV-C treatment resulted in maintenance of a high level of firmness during 15 days at low temperature and reduced the decrease in firmness during shelf-life storage. Furthermore, treated samples showed higher total flavonoids, ascorbic acid, and delayed the increases in both O₂⁻ production rate and H₂O₂ contents. However, no clear treatment effects were seen in total phenolics contents. The treatment also increased the antioxidant enzyme activities of CAT, SOD, APX and GR throughout the storage period. These results indicate that postharvest application of UV-C radiation can delay softening and enhance antioxidant capacity in shiitake mushrooms.     

High carbon dioxide and low oxygen storage effects on reactive oxygen species metabolism in Pleurotus eryngii

This study addressed the influence of high carbon dioxide and low oxygen levels on Pleurotus eryngii samples, stored at 20–25 °C and 90–95% RH for 5 d. Evaluations of sensory characteristics, malondialdehyde (MDA) content, superoxide anion (O₂⁻) production rate and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and cytochrome c oxidase (CCO) were made in the mushrooms in response to high carbon dioxide and low oxygen treatments. The results showed that 2% O₂ + 30% CO₂ significantly prolonged mushroom shelf-life when compared to the control. The 2% O₂ + 30% CO₂ mixture was better suited to maintaining mushroom sensory characteristics and delaying the MDA increase and O₂⁻ production rate during storage. The activities of SOD, POD, and CAT in 2% O₂ + 30% CO₂-treated mushrooms were significantly higher than those of the control. However, the CCO activity was not affected by the atmospheric treatment (2% O₂ + 30% CO₂). These results indicated that the 2% O₂ + 30% CO₂ treatment could alleviate lipid peroxidation and enhance antioxidant enzyme activities, but it exerted little influence on the CCO activity of Pleurotus eryngii.     

Distribution,stability and fate of phenolic compounds in white and purple eggplants (Solanum melongena L.)

Eggplants rank among the vegetables richest in antioxidants, but little is known about the allocation, stability, and turnover of these metabolites. The distribution, accumulation and degradation of phenolic antioxidants in the inner and outer pulp of two commercially important eggplant types (white and dark purple), at harvest and after 14 and 30 d of refrigerated storage under non-chilling conditions (10 °C and 90% RH) were determined in this study. Chlorogenic acid (ChA) was histolocalized by fluorescence with 2-aminoethyl-diphenylborinate and the activity of phenolic compounds oxidizing enzymes (polyphenoloxidase, PPO and peroxidase, POD) as well as H₂O₂ concentration in both fruit regions was determined. During storage, dark purple fruit were more susceptible to dehydration and showed greater deterioration than white eggplants. Both genotypes accumulated higher sugar content in the inner pulp as opposed to acids, which were more concentrated in the outer region. At harvest, pulp antioxidant capacity was similar in both eggplant types. TEAC and DPPH assays and in situ localization, showed greater total antioxidants and ChA content in the core than in the outer pulp in both white and dark purple fruit. The stability of ChA was markedly different between genotypes. In white fruit, antioxidants increased during the first two weeks of storage, remaining stable afterwards. In contrast, in dark purple eggplants, phenolic compounds declined after an initial stage at which they accumulated. PPO and POD in vitro activities, associated mainly with fruit seeds, fibers, and vascular bundles did not correlate with pulp browning or loss of phenolic antioxidants. Instead, the reduction of ChA in the core of dark purple fruit was associated with increased production of H₂O₂. Results indicate that antioxidants are predominantly located in the inner pulp of eggplants regardless of the genotype, but are more stable in white fruit. Rather than being the result of browning reactions, substantial losses of phenolic antioxidants in whole eggplants under the recommended storage conditions likely result from seed coat development and vascular lignification in the immature fruit.     

Maize yield and water balance is affected by nitrogen application in a film-mulching ridge–furrow system in a semiarid region of China

Poor soil and drought stress are common in semiarid areas of China, but maize has a high demand for nitrogen (N) and water. Maize production using the technique of double ridges and furrows mulched with plastic film are being rapidly adopted due to significant increases in yield and water use efficiency (WUE) in these areas. This paper studied N use and water balance of maize crops under double ridges and furrows mulched with plastic-film systems in a semiarid environment over four growing seasons from 2007 to 2010. To improve precipitation storage in the non-growing season, the whole-year plastic-film mulching technique was used. There were six treatments which had 0, 70, 140, 280, 420 or 560 kg N ha⁻¹ applied in every year for maize. In April 2011, spring wheat was planted in flat plots without fertilizer or mulch following four years of maize cultivation. After four years, all treatments not only maintained soil water balance in the 0–200 cm soil layer but soil water content also increased in the 0–160 cm soil layer compared to values before maize sowing in April 2007. However, under similar precipitation and only one season of spring wheat, soil water content in the 0–160 cm soil layer sharply decreased in all treatments compared to values before sowing in April 2011. Over the four years of maize cultivation, average yield in all treatments ranged from 4071 to 6676 kg ha⁻¹ and WUE ranged from 18.2 to 28.2 kg ha⁻¹ mm⁻¹. In 2011, the yield of spring wheat in all treatments ranged from 763 to 1260 kg ha⁻¹ and WUE from 3.5 to 6.5 kg ha⁻¹ mm⁻¹. The potential maximum grain yield for maize was 6784 kg ha⁻¹ with 360 kg N ha⁻¹ applied for four years, but considerable NO₃N accumulated in the soil profile. A lesser application (110 kg N ha⁻¹) to this tillage system yielded in 82% of the maximum, increased nitrogen use efficiency and mitigated the risk of nitrogen loss from the system. This study suggests that double ridge–furrow and whole-year plastic-film mulching could sustain high grain yields in maize with approximately 110 kg N ha⁻¹ and maintain soil water balance when annual precipitation is >273 mm in this semiarid environment.     

Antifungal protection and antioxidant enhancement of table grapes treated with emulsions,vapors, and coatings of cinnamon leaf oil

Table grapes have high market value in international markets due to their attractive taste and high antioxidant content. However, their market potential is limited by losses due to Botrytis cinerea Pers. Fr. Cinnamon leaf oil (CLO) is a natural fungicidal and antioxidant agent that can be used to avoid postharvest losses due to B. cinerea Pers. Fr. and to increase the antioxidant levels of this produce. CLO was applied to grapes as water emulsions (0, 0.5, 2.5, and 5 g L⁻¹), as vapors (0, 0.196, 0.392, and 0.588 g L⁻¹), or as a chemical incorporated into pectin coatings (0 and 36.1 g L⁻¹). Afterwards, berries were stored at 10 °C for 15 d and were evaluated periodically for the fungal decay index, the total phenolic and flavonoid contents and the antioxidant activity using the Trolox equivalent antioxidant capacity and DPPH radical inhibition methods. The odor acceptability of the treated berries was evaluated after 10 d of storage. The CLO emulsion (5 g L⁻¹) significantly reduced the fungal decay without affecting the antioxidant properties of the berries. The application of CLO as a vapor was more effective according to the evaluated parameters than the emulsions; all tested concentrations inhibited fungal decay and increased the flavonoid content and antioxidant activity. When CLO was incorporated into the pectin, no fungal decay appeared, and the highest antioxidant activity was observed after 15 d of storage. Additionally, all treatments, except the emulsion treatment, increased the odor acceptability of the treated berries compared to the control berries. From this study, it can be concluded that CLO as vapors or coatings can be used to control decay and increase the antioxidant health benefits of grapes due to CLO's antifungal and antioxidant properties.     

Barley–hairy vetch mixture as cover crop for green manuring and the mitigation of N leaching risk

Adopting mixtures of legumes and non-legumes can be an efficient tool to merge the advantages of the single species in the fall-sown cover crop practice. Cover crop mixtures are supposed to provide an additional benefit in reducing N leaching risks as compared to pure legume thanks to the N trapping skill of the non-legume companion, but to our knowledge no data are available on the effect of mixed cover crops on N leaching. For this reason, in a three-year study we investigated the effect of barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa Roth.) grown in 100% pure stands or in 50:50 mixtures on the N leaching below the rooting zone as compared to the bare soil. The NO₃-N concentration in the soil solution was monitored by suction cup lysimeters placed at 0.9 m depth during the whole growing cycle and after cover crop incorporation into the soil and the amount of leached N was calculated on the basis of estimated drainage.The mixture showed variable biomass accumulation and proportion in the biomass accumulated by companion species across years, but a rather constant N accumulation, with a biomass C/N ratio intermediate between those of the pure crops. In all years, the N trapping effect of the mixture was clear as it decreased NO₃-N leaching at the same level of pure barley, both during its own growing cycle and after cover crop incorporation into the soil. Pure vetch showed the highest N source potential as green manure but no NO₃-N leaching mitigation effect as compared to the bare soil. Thus we demonstrate here that a mixture of barley and vetch, which was already known to be a “self-buffered system” able to guarantee a good and rather stable N accumulation, is also a “buffering system” for the agroecosystems in the Mediterranean conditions by acting as a N trapping crop able to reduce N leaching.     

Time Course of Nitrogen in Soil Solution and Nitrogen Uptake in Maize Plants as affected by Form and Application Time of Fertilizer Nitrogen

Field experiments with silage maize were conducted in 1987 and 1988 on a loess-derived Luvisol in southwest Germany. Four nitrogen fertilizer treatments were compared: application of preplanting NH₄ N (plus a nitrification inhibitor, dicyandiamide as Didin) and preplanting NO₃-N, split application of NO₃-N (preplanting and side dressed 45 days after planting) and a control without nitrogen fertilizer in 1987 and with 64 kg N ha^?1 as calcium ammonium nitrate in 1988. The total amounts of soil mineral nitrogen (N_min+ fertilizer N) were 200 kg N ha^?1 in 1987 and 240 kg N ha^?1 in 1988. Suction cups and tensiometer were installed at five depths and samples were taken in regular intervals. Nitrate concentrations in the suction solution steeply increased at 15 cm and 45 cm soil depth 3-4 weeks after fertilizer application (1987 up to 160mgNl^?1; 1988 up to 170mgN l^?1) and steeply decreased up to 75 cm depth with the onset of intensive N uptake at shooting. Ammonium concentrations in the suction solution were very low (0-0.16 mg N l^?1). Compared to preplanting NCyN application, preplanting NH₄-N and split NO₃-N application decreased nitrate concentrations in the suction solution in spring 1987. In 1988, however, nitrate concentrations in the suction solution of preplanting NH₄-N and split NO₃-N application plots did not fall below 50mgNl^?1 at 15 cm depth during the growing season. Nitrate concentrations of split NO₃-N application increased again in autumn 1988 and hence doubled the calculated N losses by leaching during the winter months compared to preplanting N applications. At shooting, plants of the preplanting NH₄-N treatment had lower nitrate concentrations in leaf sheaths compared to plants of preplanting NO₃-N application. Total N uptake of maize between shooting and early grain filling of preplanting NH₄-N and split NO₃ -N application tended to be higher compared to preplanting NO₃-N application, reflecting the higher N availability in the soil later in the season. However, final dry matter yields and N uptake were not significantly affected by N form or time of N application. Since N losses by nitrate leaching between N application and onset of N uptake by plants were negligible on the experimental site, preplanting NH₄-N application and split NO₃-N application showed no agronomic advantages. High amounts of side dressed NO₃-N may increase nitrate leaching during the winter months, especially in years with delayed rainfall after application.     

Long-term fate of nitrogen uptake in catch crops

The long-term effects of undersowing a ryegrass catch crop in cereals was analysed with the FASSET simulation model. The model was tested on a 28-year field experiment with ryegrass catch crops in spring barley. The experiment included treatments with nitrogen (N) fertiliser rates, catch crop use and timing of tillage. The modelled effects of these treatments generally agreed with observations on crop production, soil carbon, soil nitrogen and nitrate leaching. Both the observations and the simulations predicted a yield increase of 7 kg N ha⁻¹ and an increase in nitrate leaching of 13 kg N ha⁻¹ due to a prehistory of 24 years with continuous use of catch crops compared to a prehistory without catch crops.

A range of scenarios was constructed to evaluate the fate of the reduced nitrate leaching on crop N uptake, N leaching, gaseous emissions and change in soil organic N, and how this fate interacts with soils and climate and management. These scenarios showed that 22–30% of the reduced nitrate leaching was subsequently leached during the following decades after termination of catch crop use. Between 35 and 40% of the reduced nitrate leaching was harvested in cereals. The exact distribution depended primarily on the soil texture. The scenarios showed that effects of catch crops should be evaluated on the long-term rather than consider short-term effects only.     

Transfer of Grain Legume Nitrogen within a Crop Rotation Containing Winter Wheat and Winter Barley

In a crop rotation trial, conducted from 1985 to 1988 at TU-Munich's research station in Roggenstein, the transfer of grain legume nitrogen was evaluated in crop rotations containing fababeans and dry peas as well as oats (reference crop) and winter wheat and winter barley as following crops. The results obtained can be summarized as follows: Dinitrogen fixation by fababeans ranged from 165 to 240 kg N ha¹, whereas N₂-fixation by peas amounted from 215 to 246 kg N ha^?1. In all seasons the calculated N-balance where only grain was removed was positive, with a net gain being on average 106 (peas) and 84 (fababeans) kg N ha^?1. After the harvest of peas 202 kg N ha^?1 remained on the field on average over seasons (158 kg N ha^?1 in the above ground biomass and 44 kg N ha^?1 as NO₃-N in 0–90 cm depth). As compared to peas, fababeans left 41 kg N ha^?1 less due to smaller amounts of nitrogen in the straw. After oats very small amounts of residual nitrogen (33 kg N ha^?1) were detected. After the harvest of grain legumes always a very high nitrogen mineralization was observed during autumn especially after peas due to a close C/N-relationship and higher amounts of nitrogen in the straw as compared to fababeans. In comparison with fababeans, N-mineralization after the cultivation of oats remained lower by more than 50%. During winter, seepage water regularly led to a considerable decrease of soil NO₃-N content. The N-leaching losses were especially high after cultivation of peas (80 kg N ha ^?1) and considerably lower after fababeans (50 kg N ha^?1) and oats (20 kg N ha^?1). As compared to oats, a higher NO₃-N content in soil was determined at the beginning of the growing period after preceding grain legumes. Therefore, winter wheat yielded highest after preceding peas (68 dt ha^?1) and fababeans (60 dt ha^?1) and lowest after preceding oats (42 dt ha^?1). The cultivation of grain legumes had no measurable effect on yield formation of the third crop winter barley in either of the growing seasons.     

Vorfruchtwirkurigen unterschiedlicher Rotationsbrachen auf Winterweizen

Effects of rotational fallows (‘set-aside land’) on subsequent winter wheat. The aim of the present study was to investigate the effects of different fallow treatment on subsequent winter wheat. The field trials included rotational fallows planted with Trifolium repens, Festuca rubra and Lolium perenne sown under winter barley compared to complete fallow and natural fallow without seed application and fallows planted with Trifolium pratense, Festuca rubra and Dactylis glomerata sown under winter wheat. After ploughing up the fallow vegetation, winter wheat was planted for 2 succeeding years at two levels of N-fertilization. Herbicides and fungicides were not applied. The following criteria were investigated: biomass-production, N-uptake, yield, weed infestation, nitrate and water content of the soil. In autumn, after ploughing up the fallow vegetation, the nitrate content of the soil (0—150 cm) increased by up to 210 kg NO₃-N/ha after complete fallow, by up to 60 kg NO₃-N/ha after natural fallow and by up to 75 and 130 kg NO₃-N/ha after fallows cropped with Trifolium repens and Trifolium pratense, respectively. Low nitrate levels of 20—27 kg NO₃-N/ha were observed after fallows planted with grass. N-immobilization caused by ploughing up grass fallows continued until the first harvest of the subsequent winter wheat. In the second year of winter-wheat, no differences of N-mineralization dependent on the previous fallow crop occurred, except in the case complete fallow which showed lower N-mineralization. It can be concluded that fallows cropped with grass lead to a higher nitrogen fertilizer requirement m the succeeding crops. Festuca rubra was able to form dense swards in strong competition with weeds and to decrease the abundance of Alopecurus myosuroides and Apera spíca-venti in subsequent winter wheat, while natural fallow and fallow planted with Trifolium repens and Lolium perenne caused epidemical increases in grass-weed density. Preceding crop effects on grain yield of the winter wheat showed a close relation to N-supply and were compensated by mineral N-fertilization. After natural fallow and fallow covered with Trifolinm repens, yield reductions due to grass-weed competition occurred. Undersown Festuca rubra seems to possess a special suitabihty for cultivation in routional fallows. It establishes itself strongly under different cover crops and is able to form dense swards in strong competition with weeds. Grass-weed density in the succeeding crops will be reduced and nitrate leaching will still be prevented after ploughing up the fallow vegetation. N-fertilization of the subsequent crops must be carried out under considerations of higher N-requirements which is probably not entirely due to a stronger N-immobilization.     

Nitrogen leaching from winter cereals grown as part of a 5-year ley–arable rotation

Ceramic suction cups were used to measure nitrogen (N) leaching over three consecutive winter periods from a long established ley–arable rotation experiment. We examined four treatments: 3-year all-arable, grass–clover ley and grass ley each followed by two seasons of arable test crops and an 8-year grass ley that remained as grass throughout our study. Four rates of fertilizer N were applied to sub-plots of the test crops. Our primary objective was to compare the effect that the rotations had on N leaching from the arable test crops. Cultivation of the 3-year grass and grass/clover leys and the sowing of winter wheat did not create a major flush of net N mineralization because of the unusually dry autumn weather. In the first winter following sward destruction, although the concentration of N in drainage following the grass/clover was low, it was significantly greater than that following the grass, which was greater than that from the continuous grass treatment. In contrast, the concentration and quantity of N in drainage from the all-arable treatment was at least five times greater than any other treatment. This was due to earlier and more rapid N release from the residue of the preceding arable crop. In the winters after harvest of the cereal test crops (i.e. the second and third season of measurements), the peak drainage N concentrations were similar in all treatments (20 μg NO₃-N ml⁻¹). The amount of N leached was not related to fertilizer addition. Over the full 5-year rotation, we found that the rotations that included a ley were better at conserving N; the estimated annual N leaching losses from the all-arable, grass, grass/clover and continuous grass were 29, 17, 17 and 2 kg N ha⁻¹ year⁻¹, respectively. On all treatments, but especially the grass–clover ley, the greatest rate of fertilizer addition caused a yield reduction. The N-balance indicates a considerable net immobilization during this study under the sub-plots of the arable test-crops that received N fertilizer. This corresponds to similar results of N-balance studies on other long-term experiments.     

Winter cereal yields as affected by animal manure and green manure in organic arable farming

The effect of nitrogen (N) supply through animal and green manures on grain yield of winter wheat and winter rye was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The four-course crop rotation was spring barley undersown with grass/clover – grass/clover – winter wheat or wheat rye – pulse crop. All cuttings of the grass–clover were left on the soil as mulch. Animal manure was applied as slurry to the cereal crops in the rotation in rates corresponding to 40% of the N demand of the cereal crops.Application of 50 kg NH₄–N ha^?1 in manure increased average wheat grain yield by 0.4–0.9 Mg DM ha^?1, whereas the use of catch crops did not significantly affect yield. The use of catch crops interacts with other management factors, including row spacing and weed control, and this may have contributed to the negligible effects of catch crops. There was considerable variation in the amount of N (100–600 kg N ha^?1 year^?1) accumulated in the mulched grass–clover cuttings prior to ploughing and sowing of the winter wheat. This was reflected in grain yield and grain N uptake. Manure application to the cereals in the rotation reduced N accumulation in grass–clover at two of the locations, and this was estimated to have reduced grain yields by 0.1–0.2 Mg DM ha^?1 depending on site. Model estimations showed that the average yield reduction from weeds varied from 0.1 to 0.2 Mg DM ha^?1. The weed infestation was larger in the manure treatments, and this was estimated to have reduced the yield benefit of manure application by up to 0.1 Mg DM ha^?1. Adjusting for these model-estimated side-effects resulted in wheat grain yields gains from manure application of 0.7–1.1 Mg DM ha^?1.The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH₄–N in applied manure varied from 23% to 44%. The NUE in the winter cereals of N accumulated in grass–clover cuttings varied from 14% to 39% with the lowest value on the coarse sandy soil, most likely due to high rates of N leaching at this location. Both NUE and grain yield benefit in the winter cereals declined with increasing amounts of N accumulated in the grass–clover cuttings. The model-estimated benefit of increasing N input in grass–clover from 100 to 500 kg N ha^?1 varied from 0.8 to 2.0 Mg DM ha^?1 between locations. This is a considerably smaller yield increase than obtained for manure application, and it suggests that the productivity in this system may be improved by removing the cuttings and applying the material to the cereals in the rotation, possibly after digestion in a biogas reactor.Cereal grain protein content was increased more by the N in the grass–clover than from manure application, probably due to different timing of N availability. Green-manure crops or manures with a relatively wide C:N ratio may therefore be critical for ensuring sufficiently high protein contents in high yielding winter wheat for bread making.     

Endosperm protein accumulation in wild and cultivated barley and their cross grown in spike culture

Summary The high protein wild relatives of cultivated cereals have proven difficult to utilize in plant breeding by direct selection for high grain protein percentage, and hence alternative selection criteria are needed. In this study, a spike culture method was used to measure differences in protein accumulation between wild and cultivated barley, and their cross, at different levels of nitrogen supply. Three genotypes, barley cultivar Hordeum vulgare L. cv. Clipper, a wild barley accession H. spontaneum Koch line 363, and a high protein F₅ line (38.4) derived from their cross, were grown from 8 to 27 days after flowering in in vitro spike culture. Nitrogen supply in the culture medium was either 0.4 g/l or 2.0 g/l of N supplied as NH₄NO₃. Spikes were harvested at approximately 3 day intervals during grain development, and salt soluble and hordein protein fractions were measured. Lines 363 and 38.4 differed from Clipper in having extremely high initial rates of protein accumulation, even at 0.4 g/l N. In high nitrogen conditions all three genotypes reached similar salt soluble plus hordein protein levels. Hordein-1 and hordein-2 fractions were measured separately; the percent of hordein-1 was higher in lines 363 and 38.4 than in Clipper at 0.4 g/l N. For all parameters measured, pot-grown spikes of matching age were harvested and were shown to be similar to the 0.4 g/l N treatment. The possible utilization of spike culture for identification of critical protein accumulation parameters is discussed, in relation to their possible utilization in breeding.