Modelling and measuring the effect of nitrogen catch crops on the nitrogen supply for succeeding crops

Nitrogen catch crops are grown to absorb nitrogen from the rooting zone during autumn and winter. The uptake of N (N_upt) from the soil inorganic N pool (N_min) to a pool of catch crop nitrogen, will protect the nitrogen against leaching. After incorporation, a fraction (m) of the catch crop nitrogen is mineralized and becomes available again. However, not all available nitrogen present in the soil in the autumn is lost by leaching during winter. A fraction (r) of the nitrogen absorbed by the catch crop would, without a catch crop, have been retained within the rooting zone. The first year nitrogen beneficial effect (N_eff) of a catch crop may then be expressed b N _eff = m*N _upt - r* N _upt The soil-plant simulation model DAISY was evaluated for its ability to simulate the effects of catch crops on spring N_min and N_eff. Based on incubation studies, parameter values were assigned to a number of catch crop materials, and these parameter values were then used to simulate spring Nmin. The model was able to predict much of the vairiation in the measured spring Nmin (r² = 0.48***) and there was good agreement between the measured and the simulated effect of winter precipitation on spring N_min and Neff.Scenarios including variable soil and climate conditions, and variable root depth of the succeeding crop were simulated. It is illustrated that the effect of catch crops on nitrogen availability for the succeeding crop depends strongly on the rooting depth of the succeeding crop. If the succeeding crop is deep rooted and the leaching intensity is low, there is a high risk that a catch crop will have a negative effect on nitrogen availability. The simulations showed that the strategy for the growing of catch crops should be adapted to the actual situation, especially to the expected leaching intensity and to the rooting depth of the succeeding crop.     

Growth, nutrition, and nitrogen fixation in grey alder at varied rate of nitrogen addition

Seedlings of grey alder (Alnus incana Moench), nodulated or unnodulated, were investigated at varied relative addition rate of nitrogen. Nitrogen fixation alone, without addition of mineral nitrogen, resulted in an almost optimum nitrogen status but only about half the maximum relative growth rate, probably mainly because of energy costs of nodulation and fixation. The growth deficit due to nodulation was much more than can be explained by the theoretical energy requirement for the amount of nitrogen fixed. Thus, the nitrogen fixation process was not very efficiently used. The nitrogen fixation rate was strongly stimulated by increasing nitrogen addition rate up to high levels. The fixation rate decreased rapidly close to optimum (maximum relative growth rate) and was negligible at maximum growth. A feed-back of mineral nitrogen on photosynthesis increased fixation rate with time, and the relative importance of fixation over mineral nitrogen nutrition increased. However, nitrogen fixation, also at maximum rate, supplied only a small proportion of the nitrogen amount required for maximum growth. The optimum nutrient solutions contained comparatively high nitrogen concentrations to secure free access to nitrogen. The nodules were damaged by this treatment, and it is concluded that the nitrogen additions must be adjusted to the current consumption of the plants to avoid an increased external nitrogen concentration. Strong linear regressions were found between relative growth rate, nitrogen status expressed as percentage content of fresh weight, and relative growth rate in unnodulated seedlings. There was a greater variability in nodulated seedlings than in unnodulated ones, because of the nitrogen fixation. The reactions of unnodulated grey alder were largely the same as previously reported for birch seedlings, but the maximum growth capacity was lower in grey alder. During an initial period of change in the internal nitrogen status, deficiency symptoms appeared, especially in unnodulated seedlings. As in birch, the leaves turned green again at stable nitrogen status, independent of level. The results are in sharp contrast to data from the literature where the external nitrogen concentration was used as the driving variable for the internal nitrogen status. The measured fixation rates for grey alder are much higher than those previously reported. Still, the maximum fixation rate observed is small compared to the total nitrogen uptake rate required for maximum growth, in contrast to reported relationships. These comparisons indicate that increased external nitrogen concentration obscures the real relations between mineral and fixed nitrogen, on one hand because of rapid inhibition of nitrogen fixation and, on the other hand, because of failure to obtain stable optimum nutrition and maximum growth by means of this treatment variable.     

Effects of varied nitrogen stress on growth and nutrition in three Salix clones

The ability of Salix aquatica Smith, S. fragilis L. and S. viminalis L. to absorb nitrogen at varied growth rates was investigated in nutrient solutions. The effects of five nitrogen addition rates on growth rates, nitrogen contents of the plants, nitrogen concentration of the media, and dry matter distribution between roots, stems and leaves, were studied.
These clones are highly efficient in absorbing nitrogen at low concentrations in the root medium, independent of growth rate. Strong linear regressions were found between any two of the three factors: relative rate of nitrogen supply (R_N), nitrogen content (plant), and relative growth rate (R). Dry matter production per unit nitrogen taken up and unit time (N-productivity) and per unit nitrogen taken up independent of time (N-efficiency) was closely correlated to the nitrogen status of the plant. Root development was favoured in the sub-optimum treatments, and leaf development in the optimum treatments. With regard to their ability to absorb nitrogen, these Salix clones appear satisfactory for efficient short rotation energy forestry.     

Toxicity of nitrapyrin to sunflower under different N nutrition regimes

Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH₄)₂SO₄, NH₄NO₃ and NaNO₃ to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH₄)₂SO₄>NH₄NO₃>NaNO₃. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH₄)₂SO₄ and NH₄NO₃ than as with NaNO₃. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH₄ ⁺−N nutrition relative to NO₃ ⁻−N nutrition.     

Soil mineralizable nitrogen and soil nitrogen supply under two-year potato rotations

Two-year potato rotations were evaluated for their effects on soil mineralizable N and soil N supply. Pre-plant soil samples (0–15 cm) collected from the potato year after seven rotation cycles were used to estimate soil mineralizable N using a 24 week aerobic incubation. Potentially mineralizable N (N ₀ ) ranged from 102 to 149 kg N ha^?1, and was greater after pea/white clover and oats/Italian ryegrass than after oats by an average of 35 and 22%, respectively. Labile, intermediate and stable mineralizable N pools were increased after pea/white clover compared with oats, whereas only the stable mineralizable N pool was increased after oats/Italian ryegrass. Potato plant N uptake with no fertilizer applied was greater in potato-pea/white clover compared with the three other rotations (126 vs. average of 67 kg N ha^?1). Choice of rotation crop in potato production influences both the quantity and quality of soil mineralizable N.     

Effects of varied soil nitrogen supply on Norway spruce (Picea abies [L.] Karst.)

During a seven-month period the effect of different nitrogen (N) availability in soil on growth and nutrient uptake was studied in three-year-old Norway spruce (Picea abies [L.] Karst.) trees. The plants were grown in pots on N-poor forest soil supplied with various amounts and forms (inorganic and organic) of N. Increasing supply of inorganic N (as NH₄NO₃) increased the formation of new shoots and shoot dry weight. The root/shoot dry weight ratio of new growth was drastically decreased from 1.6 in plants without N supply to 0.5 in plants supplied with high levels of NH₄NO₃. This decrease in root/shoot dry weight ratio was associated with distinct changes in root morphology in favour of shorter and thicker roots. The addition of keratin as organic N source did neither affect growth nor root morphology of the trees. The amount of N taken up by plants was closely related to the supply of inorganic N, and trees supplied with highest levels of NH₄NO₃ also had the highest N contents in the dry matter of needles and roots. In contrast, N contents in needles of trees grown without additional N, or with keratin supply, were in the deficiency range. Supply of NH₄NO₃ decreased the contents of phosphate (P) and potassium (K) and therefore markedly increased N/P and N/K ratios in the needles. On the other hand, the contents of calcium (Ca), magnesium (Mg), and manganese (Mn) in the needles were increased in the plants supplied with inorganic N, suggesting high soil availability and promotion of uptake of these divalent cations by high nitrate uptake. The observed effects on root/shoot dry weight ratio, root morphology, and mineral nutrient composition of the needles indicated that high inorganic N supply may increase above-ground productivity but at the same time decrease the tolerance of trees against soil-borne (e.g. deficiency of other mineral nutrients) stress factors. Deceased 21 September 1996 Deceased 21 September 1996     

Molybdenum nutrition of rice under low and high nitrogen level

Summary Rice (Oryza sativa L.) cv. IR8 was grown in sand culture with nutrient solutions of normal (40 ppm) nitrogen (N), and 3 times the normal nitrogen (3N) applied in the form of ammonium nitrate in combination with molybdenum as foliar spray at the rates of 0, 15. 30, and 45g per plant. In both the nitrogen concentration the foliar application of molybdenum increased the mean crop growth rates. Molybdenum application also increased nitrate reductase activity leading to higher concentration of reduced nitrogen in the tissue and thereby creating a concentration gradient for the uptake and assimilation of applied nitrogen. re]19760505     

Effects of kelp (Macrocystis integrifolia andEcklonia maxima) foliar applications on bean crop growth and nitrogen nutrition under varying soil moisture regimes

A greenhouse experiment was designed to test the effects of two kelp(Macrocystis integrifolia andEcklonia maxima) concentrates, when prepared as foliar sprays, upon bean (Phaseolus vulgaris) growth and N nutrition under three soil moisture regimes. Plant growth and developmental responses in this greenhouse experiment have demonstrated the effectiveness of the two kelp foliar sprays as plant growth regulating substances. Bean growth and developmental responses to the kelp foliar spray treatments were dependent upon the soil moisture regime to which they have been subjected. Although the two kelp foliar sprays had varying and sometimes contrasting effects on bean growth and N nutrition, which were dependent on the soil moisture treatment, their developmental effects upon the number of nodes, shoot/root ratio, leaf area ratio and specific leaf area were quite similar. A soybean callus bioassay demonstrated the presence of cytokinin-like substances and a callus growth antagonist in the kelp concentrate. Increasing dilution of the kelp concentrate disproportionately reduced the callus growth antagonist relative to the growth promoting or cytokinin-like activity.     

Estimating the contribution of nitrogen from legume cover crops to the nitrogen nutrition of grapevines using a 15N dilution technique

The aim of this controlled environment experiment was to quantify the distribution of leaf-fed-¹⁵N and canopy fed-¹³C within nodulating, non-nodulating or N fertilized non-nodulating Cicer arietinum L. and in their surrounding rhizosphere soil, excluding soil?+?root respiration. Nodulating chickpea partitioned 32% of its total N and 27% of its total recoverable C below-ground, of which only 50% of N and 36% of C were in the clean root fraction. Non-nodulating chickpea allocated equal recoverable C but slightly less N (28%) below-ground but lost less C from plant induced below-ground respiration. The importance of this below-ground partitioning for crop systems C and N balances is highlighted by their large (45% and 33%, for N and C, respectively) contribution to the total plant derived residue (recyclable) fraction. Recovered ¹⁵N and ¹³C were greater (P?<?0.05) in the outer-rhizosphere (459?µg ¹⁵N and 3.2 mg ¹³C core^?1) than in the inner-rhizosphere soil (detached from roots during freeze-drying; 18?µg ¹⁵N and 67?µg ¹³C core^?1) in relation with the relative size of these compartments. This highlights the significance of the outer-rhizosphere soil when estimating C and N budgets and quantifying rhizodeposition, and the benefit of a double (¹⁵N, ¹³C) isotope approach to determine this flow against large background soil C and N pools.     

Protein turnover in asporogenicBacillus megaterium KM under limited nitrogen supply

Protein turnover was found to take place in cells of the asporogenic strain ofBacillus mega, terium KM during the stationary phase brought about by exhaustion of a nitrogen source. Its rate measured by degradation of prelabelled proteins varied around 4%/h. however, the synthesis of proteins at the beginning of the stationary phase was slightly higher (7–8%/h). Protein turnover started already during growth in the medium with a limiting nitrogen concentration. Addition of low doses of ammonium chloride (2 μg NH₄Cl/ml and higher) to the nongrowing population at thirty min intervals stimulated protein synthesis. This resulted both in the increased incorporation of¹⁴C-leucine into proteins and in the increased synthesis of exocellular protease. On the other hand, the intracellular degradation of proteins decreased only slightly. The number of “colony forming units” in the starving population as well as in the population which was given 2 μg NH₄Cl/ml/30 min did not change during 4 h. The number of cells not exhibiting protein synthesis was negligible in both cases. Received July 22, 1 97     

Effects of plant breeding and selection on yields and nitrogen fixation in soybeans under two soil nitrogen regimes

Summary Soybeans (Glycine max (L.) Merr.) have a high N requirement which is fulfilled by soil N uptake and N₂-fixation. This study was concerned with the effects of past yield selection on N₂-fixation in soybeans.The soybean cultivars, Lincoln, Shelby, and Williams, which represent successive improvements in the Lincoln germplasm, and a non-nodulating control were planted in a soil containing¹⁵N labelled organic matter. Two replications occurred on soil previously cropped to alfalfa and two on soil previously cropped to soybeans. Plants were harvested at five growth stages and leaf area, plant weight, total N, and atom percent¹⁵N were determined. Mature grain was harvested and yield components were also determined, as well as the total N and¹⁵N content.Cultivar differences in total dry matter were only evident at physiological maturity, when Williams contained the greatest dry matter. Williams exhibited the longest period of seed formation and seed fill and also had the highest grain yield which resulted from a larger weight per seed.The N content of the cultivars did not vary until physiological maturity when Williams contained the highest percent N. The quantity of N fixed at physiological maturity was highest for Williams and lowest for Lincoln. Fixed N contained in the harvested grain was greater for Williams than for the other two cultivars. The fraction of the total plant N derived from fixation was not greatly affected by cultivar and all cultivars acquired an average of 50% of their total N through N₂-fixation.Previous cropping history greatly affected the quantity of N fixed and the fraction of the total plant N derived from fixation. Soybeans following soybeans were more dependent upon N₂-fixation than soybeans following alfalfa with the former deriving 65% of the total plant N from fixation and the latter only 32%. These soybean cultivars apparently utilized soil N first and then used N₂-fixation to satisfy their N requirement.The past selection for higher yield has resulted in soybean cultivars with improved capacities to fix atmospheric N₂ and an improved ability to take up available soil N.     

Potassium nutrition of rice (Oryza sativa L.) varieties under NaCl salinity

A salt-tolerant (Pokkali) and a salt-sensitive (IR28) variety of rice (Oryza sativa L.) were grown in a phytotron to investigate the effect of K (0, 25, 50 and 75 mg K kg^–1 soil) application on their salt tolerance. Potassium application significantly increased potential photosynthetic activity (Rfd value), percentage of filled spikelets, yield and K concentration in straw. At the same time, it also significantly reduced Na and Mg concentrations and consequently improved the K/Na, K/Mg and K/Ca ratios. IR28 responded better to K application than Pokkali. Split application of K failed to exert any beneficial effect over basal application.     

The effect of the plant growth stimulant bactozole on Rhizobium leguminosarum bv. viciae 250a and its nitrogen-tolerant mutant M-71 under varied nitrogen supply

The effect of the plant growth stimulant bactozole on the growth of Rhizobium leguminosarum bv. viciae 250a and its nitrogen-tolerant mutant M-71 and the synthesis of extracellular carbohydrates was studied. At a low content of nitrate (6 mM) in the medium, all three bactozole concentrations tested (0.001, 0.01, and 0.1%) exerted similar stimulating effects on the growth of the parent strain 250a (about 1.5-fold) and the synthesis of extracellular carbohydrates (about 2-fold). At a high content of nitrate (20 mM) in the medium, when the growth of the parent strain and the synthesis of extracellular carbohydrates were inhibited, bactozole at all three concentrations exerted only a growth-stimulating effect. At the same time, mutant M-71 showed better growth at higher concentrations of bactozole, whereas the ability of the mutant to synthesize extracellular carbohydrates decreased with increasing bactozole concentration. The cell biomass of the mutant accumulated at 20 mM nitrate was 1.8-2.5 times greater than it was at 6 mM nitrate. Bactozole enhanced the symbiosis of legume plants with both parent and mutant strains, raising the mass of plants and enhancing nodulation and the nitrogen-fixing activity of root nodules. The symbiotic parameters of mutant M-71 were better (irrespective of whether bactozole was present or not) when its inoculum was grown at a high nitrogen content (20 mM nitrate), whereas the respective parameters of the parent strain were better when it was grown at 6 mM nitrate. The inference is made that the better physiological characteristics of the mutant in the high-nitrate medium is due to its higher nitrate reductase activity (as compared with the parent strain) in both the free-living state and in legume nodules.     

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.     

N,P供给对作物排放N2O的影响研究初报

Ｎ、Ｐ供给对作物排放Ｎ_２Ｏ的影响研究初报陈欣,沈善敏,张璐,吴杰,王学强（中国科学院沈阳应用生态研究所,沈阳１１００１５）ＡｐｒｅｌｉｍｉｎａｒｙｒｅｓｅａｒｃｈｏｎｔｈｅｅｆｆｅｃｔｏｆｎｉｔｒｏｇｅｎａｎｄｐｈｏｓｐｈｏｒｕｓｓｕｐｐｌｙｏｎＮ_...     

Consumptive use and daily evapotranspiration of corn under different levels of nitrogen and moisture regimes

Summary The seasonal consumptive use, Et per day and water use efficiency (kg grain/ha-cm) of corn were determined on a sandyloam soil during winter (rain-free) season. The difference in consumptive use was less among nitrogen levels, but marked between different moisture regimes. Et per day was less in the initial stages of the growing season, attained a peak at 80% of the crop growing season, and declined later on towards maturity. Water use efficiency was found to increase with increase in N level up to 180 kg N/ha. Among the moisture regimes, higher water use efficiency was recorded under 20% ASMD.     

Production of biomass and nutraceutical compounds by Spirulina platensis under different temperature and nitrogen regimes

The cyanobacterium Spirulina platensis has been used by humans because of its nutritional and possibly medicinal effects. Our study evaluated the influence of temperature and nitrogen concentration in the medium on the production of biomass by this cyanobacterium and the biomass composition in protein, lipid and phenolic compounds. We found that at 35 degrees C there was a negative effect on biomass production but a positive effect on the production of protein, lipids and phenolics, the highest levels of these compounds being obtained in Zarrouk's medium containing 1.875 or 2.500 g l(-1) sodium nitrate. Higher biomass densities and productivity were obtained at 30 degrees C than at 35 degrees C, but nitrogen concentration appeared to have no effect on the amount of protein, lipid or phenolics, indicating that at 30 degrees C the concentration of sodium nitrate in Zarrouk's medium (2.50 g l(-1)) can be reduced without loss of productivity, an important cost-saving factor in large-scale cultivation.