Field observations on nitrogen catch crops

Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate.The natural logarithm of the total root length, measured in the top 40 cm, L_0–40 (km m^-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m^-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L_0–40 than N0 treatments. The decline in root length density, D (cm cm^-3), with depth, X (cm), was described with the function ln D = ln D₀ – qX, where D₀ is the value of D at zero depth and q the linear coefficient. D₀ was linearly related to L_0–40, without effect of species, time of observation or N supply. The ratio D₀/q, an estimate of the absolute root length, was 1.24 × L_0–40.Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.     

Forecasting of peak population density of the rose grain aphid Metopolophium dirhodum on wheat

Suction trap catches for the period 1969 to 1984 were used to develop a forecasting system for M. dirhodum. This was achieved by using the strong relationships that exist between: a) suction trap catches of Metopolophium dirhodum at Broom's Barn and populations of the aphid in fields near Norwich, and b) winter and spring temperatures and the time when the crop became unsuitable for this aphid. This forecasting system was tested in 1985, 1986, 1987 and 1988 and successfully forecast early in the season that it would not be necessary to apply aphicides in 1987 and 1988. The use of this forecasting system would have correctly indicated that aphicide application against this aphid was unnecessary in 9 out of the 16 seasons from 1969 to 1984.     

Autecology of Bradyrhizobium japonicum in soybean-rice rotations

The effect of rice culture on changes in the number of a strain of soybean root-nodule bacteria, (Bradyrhizobium japonicum CB1809), already established in the soil by growing inoculated soybean crops, was investigated in transitional red-brown earth soils at two sites in south-western New South Wales. At the first site, 5.5 years elapsed between the harvest of the last of four successive crops of soybean and the sowing of the next. In this period three crops of rice and one crop of triticale were sown and in the intervals between these crops, and after the crop of triticale, the land was fallowed. Before sowing the first rice crop, the number of Bradyrhizobium japonicum was 1.32×10⁵ g^–1 soil. The respective numbers of bradyrhizobia after the first, second and third rice crops were 4.52 ×10⁴, 1.26×10⁴ and 6.40×10² g^–1 soil. In the following two years the population remained constant. Thus sufficient bradyrhizobia survived in soil to nodulate and allow N₂-fixation by the succeeding soybean crop. At the second site, numbers of bradyrhizobia declined during a rice crop, but the decline was less than when the soil was fallowed (400-fold cf. 2200-fold). Multiplication of bradyrhizobia was rapid in the rhizosphere of soybean seedlings sown without inoculation in the rice bays. At 16 days after sowing, their numbers were not significantly different (p<0.05) from those in plots where rice had not been sown. Nodulation of soybeans was greatest in plots where rice had not been grown, but yield and grain nitrogen were not significantly different (p<0.05). Our results indicate that flooding soil has a deleterious effect on the survival of bradyrhizobia but, under the conditions of the experiments, sufficient B. japonicum strain CB 1809 survived to provide good nodulation after three crops of rice covering a total period of 5.5 years between crops of soybean.     

Evidence for a relationship between malate metabolism and activity of 1-sinapoylglucose: L-malate sinapoyltransferase in radish (Raphanus sativus L.) cotyledons

The control of malate metabolism and stimulation of 1-sinapolyglucose: L-malate sinapoyltransferase (SMT) activity in radish (Raphanus sativus L. var. sativus) cotyledons has been studied. The light-induced and nitrate-dependent activity of SMT catalyzes the formation of O-sinapoly-L-malate via 1-O-sinapoyl--D-glucose. When dark-grown radish seedlings, cultivated in quartz sand with nutrient solution containing NO ₃ ^- as the sole N source, were treated with light, SMT activity increased concomitantly with free malate in the cotyledons. This light effect was suppressed in seedlings grown in a culture medium which contained in addition to NO ₃ ^- also NH ₄ ⁺ . However, treatment with methionine sulfoximine neutralized this ammonium effect, resulting again in both rapid accumulation of malate and rapid increase in SMT activity. When seedlings grown on NO ₃ ^- nitrogen were subsequently supplied with NH ₄ ⁺ nitrogen, the accumulated level of L-malate rapidly dropped and the SMT increase ceased. The enzyme activity decreased later on, reaching the low activity level of plants which were grown permanently on NO ₃ ^- /NH ₄ ⁺ -nitrogen. An external supply (vacuum infiltration) of malate to excised cotyledons and intact seedings, grown on NO ₃ ^- /NH ₄ ⁺ -nitrogen medium, specifically promoted a dose-dependent increase in the activity of SMT. In summary these results provide evidence indicating that the SMT activity in cotyledons of Raphanus sativus might be related to the metabolism of malic acid.Abbreviation MSO L-methionine sulfoximine - SinGlc 1-O-sinapoyl--D-glucose - SinMal O-sinapoyl-L-malate - SMT 1-O-sinapoyl--D-glucose:L-malate sinapolytransferase     

The effect of soil-applied granular pesticides and irrigation on the yield of sugar beet in fields infested with Trichodorus viruliferus

In field samples taken on a grid pattern during four winters over an 80 ha farm there were many Trichodorus viruliferus (up to 3000/litre soil) in light soils but few in heavier soils. Depth samples taken during the summer showed Trichodorus to be the only nematode genus which was more numerous below plough depth than in the plough layer. In field experiments in the most heavily infested part of the farm, soil-applied granular pesticides did not increase sugar yields following the dry spring of 1982; aldicarb increased sugar yields in one experiment following the wet spring of 1983 although it, and other granular pesticides, did not affect yield in an adjacent experiment where T. viruliferus were fewer. Irrigation during the dry summer of 1983 maintained relatively large populations of T. viruliferus, whereas in unirrigated plots without aldicarb populations declined by over 50%. Economic thresholds for T. viruliferus in 1983 at Broom's Barn were about 700/litre in unirrigated soil and 300/litre in irrigated soil.     

A function for describing nitrogen uptake,dry matter production and rooting by wheat crops

The quantities,Y, of nitrogen taken up, and dry matter produced, at various times during the growth of six winter wheat crops at Rothamsted were shown to be related to thermal time,x, based on soil temperature, by a simple equation $$Y = (A^{ - 1/n} + \exp ( - kx))^{ - n} $$ whereA is the ultimate maximum ofY, n a shape factor andk a rate constant that is related toA andn throughx′, the inflexion point of the function. The value ofn was 1.5 for both N uptake and dry matter. The value ofA for N uptake,A _N , was well described by a multiple regression on sowing data,t _s , expressed as the number of days after August 31st, and rainfall,R _Apr , in the April before harvest, but no such regression could be found for the value ofA for dry matter,A _D . The rate constants,k _N andk _D , for N-uptake and dry-matter production respectively, could be related to the date of sowing and the weather through the corresponding inflexion points,x′ _N andx′ _D . Highly significant regressions were found, forx′ _N on the time,t _sf , between sowing and the return of the soil to field capacity and forx′ _D on the reciprocal oft _s . The function was used to generate N uptake curves from values ofA _N andk _N (obtained fromx′ _N ) given by inserting the appropriate values ofR _Apr ,t _s andt _sf in the regressions. These fitted measured N uptakes satisfactorily for the six crops used to obtain the regressions, and four grown subsequently, at Rothamsted, and also for six crops at Woburn. Values ofA _D had to be set arbitrarily because no regression had been found to predict them, but using these arbitrary values in the function gave dry matter curves that fitted the measurements satisfactorily for all ten Rothamsted crops and two of the Woburn crops. Tests for seasonal and site effects showed thatA _N was influenced more by differences between the two sites than by seasonal differences other than those inR _Apr , whereasA _D was strongly influenced by these seasonal differencess and very little by those between the sites.     

Modelling partitioning between structure and storage in sugar beet: Effects of drought and soil nitrogen

In the UK sugar beet is grown on contrasting soils that vary both in their nutritional status and water-holding capacities. Water shortage and low nitrogen reduce canopy growth and dry matter production, which is compensated in part by an increase in the fraction of assimilates partitioned to storage. Conversely, high nitrogen and ample water encourage growth of the canopy, increase assimilation of carbon dioxide but reduce the proportion of assimilates stored as sugar. This paper sets out to examine simple relationships between sugar yield, total dry matter and soil nitrogen in rain-fed and irrigated sugar beet crops (Beta vulgaris L.) from 46 field experiments spanning 12 years and a range of soil types, in order to improve prediction of sugar yields. Two partitioning functions were fitted to the data. The first represents a useful alternative formulation of the allometric growth function that overcomes some of the difficulties in the interpretation of the parameters. This model adequately described the seasonal progress of sugar yield (Y) in relation to total dry matter (W), but it was difficult to postulate biological mechanisms as to how the parameters should vary in relation to varying soil nitrogen or to drought. The second partitioning function, given by Y = W − (1/k) log(1 + kW), also described the data well, but had the more useful parameter, k, the decay rate of the fraction of assimilates partitioned to structural matter. This was shown to be greater in crops which had experienced significant drought and was inversely proportional to the amount of nitrogen taken up by the crops. Relationships between k and amounts of nitrogen fertilizer applied and/or amounts of residual nitrogen in the soil at sowing, however, were more variable. These could be improved by additionally taking account of soil type and rainfall following nitrogen fertilizer application in late spring. The models are a useful extension to yield forecasting models because they provide a simple means of estimating sugar yield from total dry matter in relation to factors that affect partitioning of assimilates such as drought and soil nitrogen availability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sampling for aphids by traps and by crop inspection

The catches of thirty aphid genera and species during 3 years in a suction trap at 40 ft and on a yellow cylindrical sticky trap at 5 ft at Rothamsted and Broom's Barn are tabulated. Suction-trap catches were the more consistent but both were more effective at recording the first seasonal immigration of Myzuspersicae (Sulz.) and Aphis fabae Scop, than the British Sugar Corporation crop-inspection scheme. The catches show the differential attraction to yellow by different species, the effects of local vegetation, and the seasonal distribution of aphids that are crop pests or potential vectors of viruses.     

Nitrogen fertilization to optimize the greenhouse gas balance of hemp crops grown for biomass

Nitrogen trials were carried out on hemp crops grown in Ireland over a 3 year period to identify nitrogen fertilization strategies which optimize the greenhouse gas (GHG) and energy balances of hemp crops grown for biomass. Nitrogen rates up to 150 kg N ha^?1 were used in the study. Yield increased with nitrogen rate up to 120 kg N ha^?1 for early (Ferimon), mid (Felina 32) and late maturing (Futura 75) varieties. Variety had a significant effect on yield with yields increasing with maturation date. In 2 years of the study, certain application rates of nitrogen were applied either at sowing, at emergence, after emergence or split between these dates to determine if nitrogen rates could be reduced by delaying or splitting the applications. The application of nitrogen at times later than sowing or in splits during the early part of the growing season had no significant effect on biomass yield compared with the practice of applying nitrogen at the time of sowing. Late applications of nitrogen reduced leaf chlorophyll content and height early in the growing season. Later in the growing season, there was no difference in height between treatments although the highest concentrations of chlorophyll were found in the leaves of the late application treatment. Nitrogen rate and the timing of nitrogen application had no effect on plant density. Biomass yield, net energy and net GHG mitigation increased up to an application rate of 120 kg N ha^?1, this result was independent of soil type or soil nitrogen level. Net GHG and energy balance of hemp crops grown for biomass are optimized if late maturing varieties are used for biomass production and a nitrogen rate of 120 kg ha^?1 is applied at sowing.     

Effects of temperature on the development and growth of winter wheat roots

Winter wheat was sown on 2 dates with 3 levels of nitrogen fiertiliser (0, 50 and 200 kg N ha⁻¹) in one year and on 2 sites in a followign season. Shoot and root development and growth were measured between emergence and anthesis in the first season and emergence and 7 mainstem leaves in the second. Differences in temperature and light regime led to significant differences in shoot and root development and growth between sowing dates. A thermal time-scale, based on soil surface or air temperatures, with a base of 0°C, adequately described the production of mainstem leaves and nodal root axes over all treatments. Autumn applied nitrogen had little effect on development. Shoot growth and green area index increased exponentially with thermal time prior to spring nitrogen application and the completion of canopy development. Early-sown crops had larger root systems than late-sown crops prior to winter and this divergence was retained until anthesis. The relationship between root growth and thermal time was little better than with days after sowing and was not improved by either varying the site of temperature measurement or the base temperature used for calculation. Differences in soil texture and drainage, between sites, led to significant changes in root length distribution. Although spring applied nitrogen generally increased root length, its effects were inconsistent. There was a curvilinear relation between root length and the amount of photosynthetically active radiation (PAR) intercepted; this relation was unaffected by sowing date or nitrogen treatment. The amount of root produced per unit PAR decreased as the season progressed, reflecting the decrease in the proportion of total dry matter partitioned to the root system.     

Effects of anoxic conditions on the enzymatic conversion of D,L-2-amino-thiazoline-4-carboxylic acid to L-cystine

The effects of anoxic conditions on product inhibition and the stability of L-ATC hydrolase were investigated in the conversion of D,L-2-amino-Δ²-thiazoline-4-carboxylic acid (D,L-ATC) to L-cystine using the cell free extract enzyme of Pseudomonas sp. in the presence of hydroxylamine. At L-cysteine equivalent levels, where one mole of L-cystine was counted as two moles of L-cysteine, L-cystine inhibited the L-ATC hydrolase reaction to a greater extent than L-cysteine. In air, the product occurred predominantly as L-cystine (94.9%), whereas in a nitrogen atmosphere the product occured as a mixture of L-cysteine (39.3%) and L-cystine (40.7%). As a result, less product inhibition took place in nitrogen. The activity of L-ATC hydrolase was almost fully lost after 20 h of incubation by shaking at 30 °C in air, but considerable activity remained under the anoxic conditions of nitrogen. A kinetic analysis of the reactions confirmed that reduced product inhibition and enhanced enzyme stability in nitrogen result in a more efficient enzyme reaction. The inactivation rate constant (k₁) was estimated to be 0.11 h^?1 in nitrogen and 0.22^?1 in air, indicating that the stability of L-ATC hydrolase in nitrogen was greater than in air. The values of the K_p1 and K_p2 constants related to product inhibition were 43.36 mM and 30.48 mM for L-cysteine and L-cystine, respectively, where higher values were an indication of less product inhibition. The value of the rate constant (k₂) for the oxidation of L-cysteine to L-cystine was 0.09 h^?1 in nitrogen and 1.01 h^?1 in air, suggesting that the oxidation of L-cysteine to L-cystine proceeds faster in air than in nitrogen.     

Characterization of photosynthesis of Populus euphratica grown in the arid region

Net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (L_s) of Populus euphratica grown at different groundwater depths in the arid region were measured. g _s of the trees with groundwater depth at 4.74 m (D₄) and 5.82 m (D₅) were lower and a little higher than that at 3.82 m (D₃), respectively. Compared with C _i and L_s of the D₃ trees, C _i decreased and L_s increased at 4.74 m, however, Ci increased and L_s decreased at D₅. Hence photosynthetic reduction of P. euphratica was attributed to either stomatal closure or non-stomatal factors depending on the groundwater depths in the plant locations. P _N of the D₃ trees was significantly higher than those at D₄ or D₅. The trees of D₄ and D₅ did not show a significant difference in their P _N, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.     

The influence of crop management on the water balance of lupin and wheat crops on a layered soil in a Mediterranean climate

The influence of time of sowing and sowing density on evapotranspiration and drainage loss beneath wheat (Triticum aestivum cv. Spear) and lupin (Lupinus angustifolius cv. Gungurru) crops grown on a layered soil was investigated for three seasons in a Mediterranean climate in Western Australia. The aim of the study was to investigate whether managing crops to maximise their canopy growth would increase their water use and minimise groundwater recharge contributing to dryland salinity. A soil water balance approach was used to estimate evapotranspiration, with changes in soil water content measured with a neutron water meter. The study was carried out on a layered soil typical of agricultural soils in the region with variable depth to clay (0.22–0.38 m) and a marked contrast in hydraulic properties between the topsoil and subsoil. As a result of the low permeability subsoil, a perched water table occurred in the sandy topsoil in each of the three seasons under study during winter when rainfall was high and potential evaporation low. Perched water tables persisted for 2–3 months, with hydraulic gradients consistently downward causing drainage losses to occur. Although crop management had a large influence on shoot and root development, evapotranspiration from the different treatments was generally similar. Drainage losses were not influenced by either crop type, time of sowing or sowing density, because potential evaporation and hence evapotranspiration was low during the period when drainage losses occurred. The total drainage loss measured in each season was different, with losses ranging from 20.1 to 22.2 mm in 1990, from 40.4 to 46.7 mm in 1991 and from 49.4 to 66.6 mm in 1992. The increase in drainage loss from 1990 to 1992 was a result of progressively more seasonal rainfall in 1990, 1991 and 1992. It was concluded that there was little scope to increase water use and decrease deep drainage through crop management for sites with climatic conditions where winter rainfall exceeds potential evaporation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Seasonal activity and abundance of Orosius orientalis (Hemiptera: Cicadellidae) at agricultural sites in Southeastern Australia

Orosius orientalis is a leafhopper vector of several viruses and phytoplasmas affecting a broad range of agricultural crops. Sweep net, yellow pan trap and yellow sticky trap collection techniques were evaluated. Seasonal distribution of O. orientalis was surveyed over two successive growing seasons around the borders of commercially grown tobacco crops. Orosius orientalis seasonal activity as assessed using pan and sticky traps was characterised by a trimodal peak and relative abundance as assessed using sweep nets differed between field sites with peak activity occurring in spring and summer months. Yellow pan traps consistently trapped a higher number of O. orientalis than yellow sticky traps.     

Ultra-violet induced mutants of blue-green algae

Summary Mutant strains of Anabaena cycadeae Reinke have been isolated after ultra-violet irradiation. All the four mutants described appear to be stable. They have been identified on the basis of their pigment composition, nutritional requirements, photoautotrophic growth and reaction to light. Strain 10 M ₁ ^L is a non-nitrogen-fixing mutant as indicated by its inability to grow on basal medium (AA) deficient in combined nitrogen. Strain 10 M ₁ ^L /10 M ₁ ^D is apochlorotic, and grows very slowly on medium AA-3 both in light and dark but comparatively better under the latter condition. Strain 10 M ₁ ^L /10 M ₂ ^D is deficient in -carotenoid, photosensitive and able to grow in dark only on AA-3 medium while strain 10 M ₁ ^L /10 M ₃ ^D is a photoheterotrophic nitrogen-fixer.     

Root nodulation and nitrogen accumulation and partitioning in legume crops as affected by soil solarization

Soil solarization is a preplanting technique used in hot climates to control weeds and soilborne pathogens consisting of mulching the soil surface with polyethylene sheets. The increase in temperature associated with solarized soil could affect nitrogen availability for grain legume crops through effects on nitrogen fixing soil microorganisms or other mechanisms. To examine the effects of solarization on natural root nodulation and nitrogen accumulation and partitioning in the plant, two solarization field experiments were carried out over two planting seasons, involving genotypes of both faba bean (Vicia faba) and chickpea (Cicer arietinum). The effect of sowing date was also studied in the first season. Solarization increased the maximum soil temperature by 9–10 °C in the first, and by 13–15 °C in the second season. At 5 cm below the solarized soil surface, a temperature of over 46 °C prevailed for 146 and 280 h over the two respective seasons, while this temperature was not attained in unmulched soil. Solarization delayed the initiation of nodulation and consistently reduced the nodule number per host plant, but generated an approximate doubling of mean nodule weight. The total nodule mass per plant was not affected by the treatment in the first season, but was reduced in the second season. Solarization significantly increased the concentrations of NO₃^– -N, Na⁺, Zn²⁺, Ca²⁺ and K⁺ in the soil extract, and the total nitrogen accumulated in the whole plant. This latter increase was due to both higher plant growth and a greater plant nitrogen concentration. The increased nitrogen level in the plant was not uniform with respect to plant component, varying from 57% in the roots to 198% in the pods and seeds. The plants grown in non-solarized soil accumulated about 31% of their total N content in the shoots of the parasitic weed Orobanche crenata. Solarization dramatically improved grain yield by 300–900% in both seasons and in all genotypes studied, due to increased N availability in soil, N accumulation in plants, improved plant growth, and complete control of the parasite weed O. crenata. On the basis of these beneficial effects, soil solarization, which avoids site contamination and is suited to organic farming, should be a good opportunity in Mediterranean areas where the level and stability of grain yields are low, and the infestation of O. crenata is high.     

Distinctive and Synergistic Signaling of Human Adenosine A2a and Dopamine D2L Receptors in CHO Cells

Adenosine A_2a receptor (A_2aR) colocalizes with dopamine D₂ receptor (D₂R) in the basal ganglia and modulates D₂R-mediated dopaminergic activities. A_2aR and D₂R couple to stimulatory and inhibitory G proteins, respectively. Their opposing roles in regulating neuronal activities, such as locomotion and alcohol consumption, are mediated by their opposite actions on adenylate cyclase, which often serves as “co-incidence detector” of various activators. On the other hand, the neural actions of A_2aR and D₂R are also, at least partially, independent of each other, as indicated by studies using D₂R and A_2aR knock-out mice. Here we co-expressed human A_2aR and human D_2LR in CHO cells and examined their signaling characteristics. Human A_2aR desensitized rapidly upon agonist stimulation. A_2aR activity (80%) was diminished after 2 hr of pretreatment with its agonist CGS21680. In contrast, human D_2LR activity was sustained even after 2 hr and 18 hr pretreatment with its agonist quinpirole. Long-term (18 hr) stimulation of human D_2LR also increased basal cAMP levels in CHO cells, whereas long-term (18 hr) activation of human A_2aR did not affect basal cAMP levels. Furthermore, long-term (18 hr) activation of D_2LR dramatically sensitized A_2aR-induced stimulation of adenylate cyclase in a pertussis toxin-sensitive way. Forskolin-induced cAMP accumulation was significantly increased after short-term (2 hr) human D_2LR stimulation and further elevated after long-term (18 hr) D_2LR activation. However, neither short-term (2 hr) nor long-term (18 hr) stimulation of A_2aR affected the inhibitory effects of D_2LR on adenylate cyclase. Co-stimulation of A_2aR and D_2LR could not induce desensitization or sensitization of D_2LR either. In summary, signaling t hrough A_2aR and D_2LR is distinctive and synergistic, supporting their unique and yet integrative roles in regulating neuronal functions when both receptors are present.     

Separation of D-forms and L-forms of DL-aspartic acid derivatives by the enzyme subtilisin DY

The ability of the enzyme subtilisin DY for the synthesis of derivatives of DL-aspartic acid which are differently N and C-terminal protected and semiproducts of the peptide synthesis was investigated. The enzyme reaction was characterized by high yields and a comparatively short reaction time. Two of the substrates, Z-D,L-Asp-(OMe)₂ and PhAc-D,L-Asp-(OMe)₂, were hydrolyzed for about 15 min; the reaction time for Boc-D,L-Asp-(OMe)₂ was 2.5 h. The values for the MICHAELIS constants obtained for Z-D,L-Asp-(OMe)₂ (K_m = 0.576 mM) and PhAc-D,L-Asp-(OMe)₂ (K_m = 0.300 mM) showed a high affinity of the enzyme to the substrates. For Boc-D,L-Asp-(OMe)₂ the affinity of the enzyme is considerable lower (K_m = 14.07 mM). The results of these investigations can be effectively used for the separation of N-protected derivatives of D,L-aspartic acid and with a high probability also for other amino and racemic forms.     

The growth and nitrogen uptake of Rhodes grass grown on soils with varying histories of legume cropping

Summary Rhodes grass (Chloris gayana) was grown under glasshouse conditions on soils that had previously grown from 1 to 6 soybean (Glycine max) or Siratro (Macroptillium atropurpureum) crops. Soil mineral N contents at sowing were higher in Siratro-cropped than soybean-cropped soils and increased with cropping history.Yields of Rhodes grass at the first harvest (14 weeks) were related to soil mineral N levels at sowing by the relationship Y=138.7 (1–0.917e^–0.012x). Grass grown on all soybean soils was responsive to N at both harvests (14 and 28 weeks). Grass grown on soil that had grown three or more Siratro crops was non-responsive to N at the first harvest but responses to N were recorded on all Siratro soils at the second harvest.The amount of N removed by the grass crops was small in relation to the total amount present in the soil system. This resulted in no change in soil total N levels over the two crop periods.These results highlight the need to study N dynamics in crop systems rather than continue to measure N pool sizes when evaluating the contribution of biologically fixed N to the nutrition of subsequent non-legume crops.     

Effect of deep and shallow root systems on the dynamics of soil inorganic N during 3-year crop rotations

Unused inorganic nitrogen (N_inorg) left in agricultural soils will typically leach to deeper soil layers. If it moves below the root zone it will be lost from the system, but the depth of the root zone depends on the crop species grown. In this experiment we studied the effect of 3-year crop sequences, with different combinations of deep-rooted and shallow-rooted crops, on soil N_inorg dynamics to 2.5 m soil depth and the possibility of crop utilization of N leached to deep soil layers. We grew ten different crop sequences for 3 years. The crops and catch crops grown were selected to allow different sequences of deep-rooted and shallow-rooted crops. Very different rooting depths were obtained, from only 0.5 m (leek), to ∼1.0 m (ryegrass and barley), 1.5 m (red beet), 2.0 m (fodder radish and white cabbage) and more than 2.5 m by the chicory catch crop. The results showed a significant retention of N_inorg within the 2.5 m soil profile from one year to the next, but the retained N had leached to deeper parts of the profile during the winter season. Only little N_inorg was retained over two winter seasons. The retention in the deeper soil layers allowed N_inorg to be taken up by succeeding deep-rooted main crops or catch crops. The effects of crop rooting depth on N_inorg in the subsoil layers from 1.0 to 2.5 m were striking. White cabbage reduced N_inorg below 1.0 m with up to 113 kg N ha^-1 during its growth. Grown after catch crops, leek and red beet left on average 60 kg N ha⁻¹ less below 1.0 m than leek and red beet grown without a preceding catch crop. We conclude that it is possible to design crop rotations with improved nitrogen use efficiency by using the differences in crop rooting patterns; deep-rooted crops or catch crops can be used to recover N_inorg leached after previous crops, and catch crops can be grown before shallow-rooted crops to lift the deep N_inorg up to layers where these crops have their roots.