High Levels Of Nitrogen Fertilization Research Articles

Combined Application of Nitrogen and Phosphorus Promotes the Growth and Nutrient Accumulations of Cinnamomum camphora Container Seedlings

Combining the application of nitrogen and phosphorus is widely recognized as an effective measure to promote seedling growth. The purpose of this study was to investigate the effects of the combined application of nitrogen and phosphorus on the growth and nutrient status of C. camphora container seedlings. Exponential fertilization was applied to a range of fertilizers, including single nitrogen fertilizer, single phosphorus fertilizer, and combinations of nitrogen and phosphorus to C. camphora. Eight distinct fertilization levels of treatment (CK, N1, N2, N3, P, N1P, N2P, and N3P) were established. The height and ground diameter of the seedlings were determined periodically in each treatment group. Biomass, root system (including root length, root surface area, and root volume), and nutrient accumulation (content of soluble sugars, soluble proteins, and starch in the root system, stems, and leaves) were determined for each treatment group of seedlings. The N3P treatment (N: 9000 mg∙plant−1 + P: 6000 mg∙plant−1) had the most significant effect on the height and ground diameter of C. camphora container seedlings, while the N3 treatment (N: 9000 mg∙plant−1) proved to be the most beneficial for biomass accumulation among the eight different fertilizer levels. In addition, a single P fertilizer (P: 6000 mg∙plant−1) emerged as the most effective fertilizer for enhancing root morphology (root length, root surface area, root volume, and root average diameter) and accumulating nutrient composition (soluble sugar, soluble protein, and starch). Furthermore, it was discovered that a high level of nitrogen fertilization hindered the accumulation of nutrient composition in C. camphora container seedlings. Our comprehensive analysis revealed that nitrogen fertilizer promoted the morphological growth of C. camphora container seedlings, while phosphorus fertilizer proved to be the most beneficial for root growth and nutrient composition accumulation. Additionally, it was emphasized that controlling the quantity of nitrogen fertilizer is also a crucial measure.

Enhanced suppression of saprotrophs by ectomycorrhizal fungi under high level of nitrogen fertilization

Ectomycorrhizal fungi (EMF) are widespread in northern conifer forests. By competing with the free-living saprotrophic fungal and bacterial communities for limited soil nitrogen, EMF are expected to suppress litter decomposition and thus drive soil carbon accumulation. The EMF may also stimulate rhizosphere microbial growth through inputs of labile plant carbon, and subsequently contribute to the soil carbon pool via microbial necromass. Here we examined the relative strength of these two potential EMF effects in a northern conifer plantation of the Saihanba Forest, the largest plantation in China. The soil fungal and bacterial biomass, as well as their respiration, were quantified within the two types of soil cores that either allow or exclude the ingrowth of EMF. We also set up a nitrogen fertilization gradient (0, 5, 10, 15 g N m–2 y–1) in this plantation to quantify the influence of external inorganic nitrogen on the EMF effects. We found evidence that EMF inhibit the overall fungal and bacteria biomass, confirming the suppression of saprotrophs by EMF. In addition, high levels of external nitrogen fertilization (15 g N m–2 y–1) might further enhance the suppression by EMF. In contrast, the presence of EMF consistently increased soil microbial respiration across all nitrogen fertilization levels, indicating that the carbon allocated to EMF could have been largely consumed by microbial respiration and contributed minimally to the accumulation of microbial biomass. Our results also indicated that the suppression of saprotrophs by EMF may play a critical role in driving continuous soil carbon accumulation in this northern pine plantation under atmospheric nitrogen deposition.

INFLUÊNCIA DA ADUBAÇÃO NO TEOR DE NITRATO NAS PASTAGENS E NO LEITE AO LONGO DO ANO NO OESTE DE SANTA CATARINA

The indiscriminate use without criteria of nitrogen fertilization can lead to an accumulation of nitrate in pastures, animal poisoning and potential increase in residual content of this compound in milk. The objective of this study was to determine the residual levels of nitrate throughout the year in pastures and milk from small farms in western Santa Catarina (SC) that use high levels of nitrogen fertilization. The experiment was carried out from April/2018 to March/2019 on 10 dairy farms in the municipality of Riqueza (SC). Two annual collections of water samples and monthly collections of pastures and milk were carried out, in addition to obtaining information on the property and management of pasture fertilization through a structured questionnaire. Nitrate was also evaluated in pastures using the diphenylamine test. Temperature and rainfall data were obtained daily by a weather station. The average amount of nitrogen fertilizer used in the properties was 654 ± 176 kg/ha/year. The average nitrate content in the drinking water of the animals was 1.5 ± 1.4 mg/L, in the pasture it was 270 ± 76 mg/kg DM, while in milk it was 2.0 ± 0.3 mg/L. There was seasonal variation with an increase in nitrate content in pastures and milk in autumn, a period of the experiment in which low rainfall was observed. It was concluded that despite being dairy properties with high use of nitrogen fertilization, safe milk is produced in terms of nitrate levels, even in times of the year with adverse climatic conditions. The diphenylamine test has a good ability to discriminate the nitrate content in pastures and can be indicated as a quick test to verify the presence of high levels of nitrate in the pasture.

Enhanced Suppression on Saprotrophs by Ectomycorrhizal Fungi Under High Level of Nitrogen Fertilization

Enhanced Suppression on Saprotrophs by Ectomycorrhizal Fungi Under High Level of Nitrogen Fertilization

Maize Response to Population under High Levels of Nitrogen Fertilization

To investigate the response of maize hybrids to plant population and nitrogen fertilization rates. Two field experiments were conducted at the Experimental Farm, Faculty of Agriculture (Saba Basha), Alexandria University during 2018 and 2019 seasons. Factorial experiments (two factors) in randomized complete block design (RCBD). Whereas, the first factor was plant population (50000, 75000, 100000 plant/ha), while, the second factor was nitrogen fertilization rates (216, 288, 360, and 432 kg N/ha). The results revealed that ear length (cm), number of rows/ear, number of grains/row, number of grains/ear, 100-grains weight (g), grain yield (t/ha), straw yield, biological yield (t/ha), harvest index (%) and grain protein content (%) of maize hybrid were, significantly, affected by plant population and nitrogen fertilizer rates, where the highest grain yield was obtained by growing maize plant hybrid 3444 at a population of 75000 plant/ha under the application of 360 kg N/ha under the environmental conditions of Alexandria, Egypt.

Milk production per cow and per hectare of spring-calving dairy cows grazing swards differing in Lolium perenne L. ploidy and Trifolium repens L. composition

Grazed grass is the cheapest feed available for dairy cows in temperate regions; thus, to maximize profits, dairy farmers must optimize the use of this high-quality feed. Previous research has defined the benefits of including white clover (Trifolium repens L.) in grass swards for milk production, usually at reduced nitrogen usage and stocking rate. The aim of this study was to quantify the responses in milk production of dairy cows grazing tetraploid or diploid perennial ryegrass (Lolium perenne L.; PRG) sown with and without white clover but without reducing stocking rate or nitrogen usage. We compared 4 grazing treatments in this study: tetraploid PRG-only swards, diploid PRG-only swards, tetraploid with white clover swards, and diploid with white clover swards. Thirty cows were assigned to each treatment, and swards were rotationally grazed at a farm-level stocking rate of 2.75 cows/ha and a nitrogen fertilizer rate of 250 kg/ha annually. Sward white clover content was 23.6 and 22.6% for tetraploid with white clover swards and diploid with white clover swards, respectively. Milk production did not differ between the 2 ploidies during this 4-yr study, but cows grazing the PRG-white clover treatments had significantly greater milk yields (+596 kg/cow per year) and milk solid yields (+48 kg/cow per year) compared with cows grazing the PRG-only treatments. The PRG-white clover swards also produced 1,205 kg of DM/ha per year more herbage, which was available for conserving and buffer feeding in spring when these swards were less productive than PRG-only swards. Although white clover is generally combined with reduced nitrogen fertilizer use, this study provides evidence that including white clover in either tetraploid or diploid PRG swards, combined with high levels of nitrogen fertilizer, can effectively increase milk production per cow and per hectare.

Short-term impacts of high levels of nitrogen fertilization on soil carbon dynamics in a tropical pasture

Bermudagrass (Cynodon spp.) is widely recognized by its ability to respond positively to nitrogen (N) fertilization. Nitrogen often promotes shoot and root growth and, consequently, increase carbon (C) inputs into the soil via above- and below-ground biomass. The objective of this 2-yr field study was to assess the short-term effects of increased N levels on soil C dynamics of a Tifton 85 bermudagrass pasture grown in a tropical soil. Treatments consisted of five levels of N fertilization (0, 60, 120, 180 and 240 kg ha−1 N) applied at each harvest for a total of four harvest events per year. Soil samples were collected at the 0 to 0.1 and 0.1 to 0.2 m depths for determination of soil C content. The latter was also fractionated into free-light (FLF), particulate organic carbon (POC), and mineral-associated organic carbon (C-min) fractions. Results indicated that N levels showed no effect on total C content and distribution among the various size-density fractions. The top layer (0–0.1 m) was more sensitive to changes in soil C for more recalcitrant fractions (POC and C-min) relative to 0.1–0.2 m layer. Our findings suggest that acceleration of the decomposition rate induced by N fertilization may have offset the potential accumulation of soil C associated with high inputs of above- and below-ground biomass, but additional research is warranted to better elucidate long-term impacts of nitrogen fertilization on soil C dynamics in grassland of tropical regions.

A 30-years vineyard trial: Plant communities, soil microbial communities and litter decomposition respond more to soil treatment than to N fertilization

Soil management strategies in viticulture should not only aim to optimize yield and quality of grapevines, but also sustain soil biodiversity and soil functioning. Here, we report on the combined effects of soil treatment and nitrogen fertilization on parameters related to soil fertility and litter decomposition, as well as plant, fungal, and bacterial communities in a long-term vineyard experiment, where these management practices have been applied since 1987. Plots in this vineyard (Hesse, Germany) were treated with different yearly amounts of nitrogen fertilizer (0, 30, 60, 90, 120, and 150 kg N ha−¹) with two types of inter-row soil treatment (tillage vs. permanent cover). We analyzed soil properties of the topsoil, decomposition parameters using the Tea Bag Index approach, the inter-row plant community, and microbial communities (bacteria and fungi) by next generation sequencing techniques.Long-term tillage decreased soil carbon and nitrogen levels as well as some plant available nutrients, whereas soil pH and plant available phosphorus increased. Elevated amounts of nitrogen fertilization slightly increased soil carbon and nitrogen levels. Relative mass loss of tea bag content due to decomposition was decreased, while stabilization of labile litter components was increased by tillage, compared to permanent cover treatments. Plant community patterns were changed by soil treatment with tillage inter-rows exhibiting annual, ruderal species and being more diverse compared to permanent cover inter-rows. Relative abundance of several bacterial phyla and fungal orders responded strongly to soil treatment. Changes in soil pH and levels of phosphorus could partly explain the underlying mechanisms involved in shifts of bacterial and fungal communities, respectively. In contrast, long-term nitrogen fertilization only slightly shifted plant and microbial community composition. This study shows that over the long-term, soil treatment strongly affects soil functioning and biodiversity, exceeding the effect of even high nitrogen fertilization levels.

Effects of elevated atmospheric CO2 and nitrogen fertilization on nitrogen cycling in experimental riparian wetlands

Studies on the relationship between plant nitrogen content and soil nitrogen reduction under elevated CO2 conditions and with different nitrogen additions in wetland ecosystems are lacking. This study was meant to assess the effects of elevated CO2 concentrations and inorganic nitrogen additions on soil and plant nitrogen cycling. A cultured riparian wetland, alligator weeds, and two duplicated open top chambers (OTCs) with ambient (380 μmol/mol) and elevated (700 μmol/mol) CO2 concentrations at low (4 mg/L) and high (6 mg/L) nitrogen fertilization levels were used. The total plant biomass increased by 30.77% and 31.37% at low and high nitrogen fertilization levels, respectively, under elevated CO2 conditions. Plant nitrogen content decreased by 6.54% and 8.86% at low and high nitrogen fertilization levels, respectively. The coefficient of determination (R2) of soil nitrogen contents ranged from 0.81 to 0.96. Under elevated CO2 conditions, plants utilized the assimilated inorganic nitrogen (from the soil) for growth and other internal physiological transformations, which might explain the reduction in plant nitrogen content. A reduction in soil dissolved inorganic nitrogen (DIN) under elevated CO2 conditions might have also caused the reduction in plant nitrogen content. Reduced plant and soil nitrogen contents are to be expected due to the potential exhaustive use of inorganic nitrogen by soil microorganisms even before it can be made available to the soil and plants. The results from this study provide important information to help policy makers make informed decisions on sustainable management of wetlands. Larger-scale field work is recommended in future research.

Effect of protection against pathogens on yield of two breeding types of winter oilseed rape cultivars under high level of nitrogen fertilization

Effect of protection against pathogens on yield of two breeding types of winter oilseed rape cultivars under high level of nitrogen fertilization

Linseed (Linum usitatissimum) as an oil crop in organic farming: abiotic impacts on seed ingredients and yield

Linseed contains substantial amounts of desired ingredients, such as omega-3 fatty acids (α-linolenic acid) and antioxidants, as well as undesired ingredients such as cyanogenic glycosides and cadmium. This paper presents and discusses the abiotic factors which influence quality and yield of linseed seeds in organic cropping systems. In temperate climates, conventional farmers can harvest more than 2.0 t seed ha−1, with oil contents ranging from 35 to 44 %. Organic trials usually had lower yields with up to approximately 1.8 t seed ha−1 in temperate, continental, and Mediterranean conditions. Cool climatic conditions in temperate regions lead to high shares (>60 %) of omega-3 fatty acids related to total oil content in organic farming as well as in conventional farming. Linseed achieved maximum yields of seeds and omega-3 fatty acids with a fertilization level of less than approximately 110 kg nitrogen ha−1. High levels of nitrogen fertilization did not benefit the content of omega-3 fatty acids; increasing the nitrogen fertilization from 52 to 260 kg ha−1 reduced the content of α-linolenic acid by 7.25 % in a trial. The content of cyanogenic compounds turned out to be positively correlated with the protein content of the seeds and the nitrogen fertilization; therefore, the usually moderate level of nitrogen supply in organic crop rotations could keep the content of cyanogenic glycosides on a comparatively low level, compared to cropping systems with higher nitrogen levels. Linseed is a hyper-accumulator of cadmium; the total cadmium content in the seeds is determined by the cadmium content of the soil and the linseed variety. Generally, the choice of linseed variety influences the quality of the seed, and respective varieties must be chosen to improve product quality. Harvest, post-harvest, and processing conditions additionally affect seed and oil quality. Heating can reduce the unwanted cyanogenic glycosides, but it also reduces the content of desired anti-oxidants and of omega-3 fatty acids.

Response of leaf endophytic bacterial community to elevated CO2 at different growth stages of rice plant.

Plant endophytic bacteria play an important role in plant growth and health. In the context of climate change, the response of plant endophytic bacterial communities to elevated CO2 at different rice growing stages is poorly understood. Using 454 pyrosequencing, we investigated the response of leaf endophytic bacterial communities to elevated CO2 (eCO2) at the tillering, filling, and maturity stages of the rice plant under different nitrogen fertilization conditions [low nitrogen fertilization (LN) and high nitrogen fertilization (HN)]. The results revealed that the leaf endophytic bacterial community was dominated by Gammaproteobacteria-affiliated families, such as Enterobacteriaceae and Xanthomonadaceae, which represent 28.7–86.8% and 2.14–42.6% of the total sequence reads, respectively, at all tested growth stages. The difference in the bacterial community structure between the different growth stages was greater than the difference resulting from the CO2 and nitrogen fertilization treatments. The eCO2 effect on the bacterial communities differed greatly under different nitrogen application conditions and at different growth stages. Specifically, eCO2 revealed a significant effect on the community structure under both LN and HN levels at the tillering stage; however, the significant effect of eCO2 was only observed under HN, rather than under the LN condition at the filling stage; no significant effect of eCO2 on the community structure at both the LN and HN fertilization levels was found at the maturity stage. These results provide useful insights into the response of leaf endophytic bacterial communities to elevated CO2 across rice growth stages.

Economic Efficiency of Different Agricultural Practices of “Panicum virgatum L. (switchgrass)” for Fodder Production

Switchgrass is a multipurpose perennial crop characterized by high yield (for fodder or raw material for pellet production) under low inputs conditions. This study sought to analyse the economic efficiency of different cultivating practices of switchgrass for hay or silage production. To assess the economic efficiency, three-year field experiments were established in two contrasting environments in central Greece (Palamas and Velestino) and contained two experimental factors: quantity of irrigation water (two levels: 0 and 250 mm) and applied nitrogen fertilization (four levels: 0, 80, 160 and 240 kg N ha-1). Moreover, the costs of four different harvest methods (three different types of straw-bales for hay production and silage) were taken into account. The results demonstrated that production cost is largely depended on the harvesting practice. In addition, an attractive income of 1,745 €/ha (the higher one at Palamas site) for fodder production was found. The efficiency scores follow the same tendency at both sites, verifying that there is no necessity of high levels of nitrogen fertilization in order to improve switchgrass production efficiency. These data suggest that switchgrass is attractive as a fodder crop in regions with high precipitation or in areas with a moderately shallow groundwater table and should be seriously taken into consideration for future land use systems in Greece and more generally in the Mediterranean basin.

Energy crops on less favoured (alkaline) soil

The reduction in fossil energy and row material sources induces growing demand for renewable resources. The growing demand for herbal raw materials has land use impacts as well. One way to reduce the conflict between the food and energy crops can be the utilization of less favored areas by growing energy crops. Among the potentially available areas for this purpose the salt affected soils (SAS) occupy a significant territories. SAS with structural B-horizon (meadow solonetz soils) represent the most wide spread group of SAS in Hungary. About half of these soils have been reclaimed and used as arable land and the remaining 50% are used as grassland. Sweet sorghum production for manufacturing of alcohol production was investigated in a long term amelioration and fertilization experiment on a salt affected soil (meadow solonetz). By means of regression analyzes the effect of sodium content of the soil and increasing mineral fertilizer doses were studied. According to the multiple regression analysis only the effect of nitrogen fertilizer was significant. On the solonetz type salt affected soil the effect of water soluble salt content of the soil was not significant, but there was a closer correlation between the ammonium-lactate sodium content and the yield of sweet sorghum. The maximum green mass was 45–50 t ha-1, in the case of low Na content and high level of nitrogen fertilization.
 In order to quantify the potential yield of natural grass vegetation the relationship between the soil forming processes and the grass vegetationwas investigated. Beyond the different forms of Na-accumulation, the spatial pattern (mosaic-like characteristic) is also an inseparable feature of salt affected soils. The difference in the water regime, caused by the micro-relief is the main cause of variability. The run-on water keeps the deeper parts of the catena position wet longer. The wet situation causes more intensive leaching. In the low-laying parts of salt affected soils species preferring wet situations (mainly Alopecurus pratensis) are in majority. On the higher parts of the micro-relief species tolerating dry situations (mainly Festuca pseudovina) are dominant. The yearly grass production of low laying areas can be 4–7 t ha-1 but because of prolonged wet conditions the grass is not grazed and mowing can only be in old state. This old grass is not proper for feeding, but it may be suitable as energy plant.

Involvement of Carbohydrate, Protein and Phenylanine Ammonia Lyase in Up-Regulation of Secondary Metabolites in Labisia pumila under Various CO2 and N2 Level

A split plot factorial 2 × 3 experiment was designed to examine and characterize the relationships among secondary metabolites (total phenolics, TP; total flavonoids, TF), carbohydrate content, C/N ratio, protein synthesis and L–phenylalanine ammonia lyase (PAL; EC 4.3.1.5) activity in the Malaysian medicinal herb Labisia pumila (Blume) Fern-Vill. under different CO2 concentrations (400 = ambient and 1,200 µmol mol−1 CO2) and three levels of nitrogen fertilization (0, 90 and 270 kg N ha−1) for 15 weeks. The interaction between CO2 and nitrogen levels imposed a significant impact on plant secondary metabolite production, protein, PAL activity and fructose levels. Highest TP and TF were recorded under 1,200 µmol mol−1 CO2 when N fertilizer was not applied; lowest values were obtained at 400 µmol mol−1 CO2 fertilized with the highest N level. Concurrently, fructose contents increased tremendously. Increase in fructose content might also enhance erythose-4-phosphate production (substrate for lignin and phenolic compounds), which shares a common precursor transdalolase in the pentose phosphate pathway. PAL activity was noted to be highest under 1,200 µmol mol−1 CO2 + 0 kg N ha−1 coinciding with subsequent recording of the lowest protein content. The results implied that the increase in plant secondary metabolites production under the tested conditions might be due to diversion of phenylalanine for protein synthesis to production of secondary metabolites. It was also found that the sucrose to starch ratio was also high under high levels of nitrogen fertilization, indicating an enhanced sucrose phosphate synthase activity (SPS; EC 2.4.1.14) under such condition.

Changes in the survival rate and fecundity of the rice leaffolder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae), at different magnesium concentrations in hydroponic culture

The rice leaffolder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae), is a leaf-feeding pest and the physical and chemical nature of the rice leaf affects its feeding, survival and fecundity. We examined changes in the survival rates of larvae and pupae, pupal weight and the number of eggs laid by adult females developed from a resistant variety (Huaidao 9) and a susceptible variety (Yangjing 9538) in hydroponic solutions containing different concentrations of magnesium (Mg). The concentration of Mg in the hydroponic solution significantly affected the survival rates of the larvae and pupae, the pupal weights and the numbers of eggs laid. Larval survival rates on the resistant variety were significantly higher for fourth instars exposed to 60 and 80 ppm Mg and pupae exposed to 20, 40, 60 and 80 ppm Mg than those for the control treatment (without Mg). For the susceptible variety, survival rates of first, second and third instars were significantly higher at high concentrations of Mg than those under control conditions. In addition, the number of eggs laid by adult females increased with increasing Mg concentrations, though there was a slight decrease at 80 ppm compared to 60 ppm. These results indicate that Mg is beneficial to the development, survival and fecundity of C. medinalis. They further suggest that high levels of nitrogen fertilizer in rice fields favour outbreaks of this pest because application of nitrogen elevates the chlorophyll content and Mg levels in the rice leaf.

Long-term effect of fertility management on the soil nematode community in vegetable production under greenhouse conditions

Nematode trophic groups and functional guilds were monitored after long-term fertilization regimes in a vegetable greenhouse, where no fertilizer, organic manure, two different levels of inorganic fertilizers and the combined applications of manure with different levels of inorganic fertilizers were compared. Significant treatment effects were observed in the abundance of total nematodes and the composition of different trophic groups. Compared with other fertilizer treatments, manure fertilizer increased the abundance of total nematodes, and the relative abundance of bacterivores, while the relative abundance of plant parasites decreased. The relative abundance of plant parasites and fungivores increased, and that of bacterivores decreased following the applications of N fertilizer in July. High levels of nitrogen fertilizer decreased the relative abundance of omnivore–carnivores. The values of the basal index and channel index decreased in the treatments with manure and increased following the N fertilizer compared to the control. Nematode faunal analysis indicated that soil food webs in the treatments with manure were disturbed, and those in the treatments with inorganic fertilizers were degraded due to the relatively lower soil pH and higher electrical conductivity induced by the high level of nitrogen fertilization.

Effect of seeding rate, Nitrogen levels and rate of application of herbicides on growth of bread wheat

A field trial was conducted at the experimental farm, Department of Field Crop Science, College of Agriculture, University of Baghdad, Abu-Ghraib in 2001/2002 and 2002/2003 seasons to investigated the effect of seeding rate (120, 180 and 240 kg.ha‌2), nitrogen levels ( 240, 300 and 360 N kg.ha-2) and rate application of herbicides (Topic 250 gm a.i ha-1+ Logran 125 gm a.i ha-1 and Topic 500 gm+ Logran 250 gm a.i ha-1). A randomized complete plot design (RCBD) according to split – split plot was used with three replications. The following results could be summarized as follow : Rate seeding 240 kg.ha-1 gave a high value of leaf area index (6.1 and 6.9) dry weight of crop (509.6 and 670.4 gm.m‌-2), rate growth of crop (41.0 and 46.0 gm.m‌-2.day-1) and net assimilation rate (5.7, 6.0 gm.m‌-2.day-1)in the two seasons respectively. In both seasons 2001/2002 and 2002/2003 and at all stage growth of plant especially at stage 102 day from date planting. The high level of nitrogen fertilization 360 kg.ha-1 caused increasing of most characteristic as leaf area index, dry weight of plant, rate growh of crop and net assimilation rate. The treatment recommendation of Topic and Logran at first season gave high value of leaf area index (6.1) and rate growth of crop (41.9 gm.m-2 day) at second season. The treatment of full recommendation of rate application of Topic and Logran gave high value of leaf area index (7.5) and dry weight of plant (484.4 gm.m‌-2.day-1). Rate of seeding 240 kg.ha-1 with 360 kg.N.ha 1 gave in both seasons high value of leaf area index 6.6, 7.2 dry weight of crop (699.2, 597.2 gm.m-2) and rate growth of crop (43.7 and 47.7 gm.m-2.day-1) respectively.The treatment recommendation of Topic and Logran with nitrogen fertilization 360 kg N.ha-1 at first season gave high value of leaf area index 6.6 but at second season gave full recommendation high value 8.0. From these results we can conclusion that the wheat is positive response to study factors, so we can use competition method to control a weed, instead of herbicide in order to keep clean environment.

The economic opportunities for increasing the use of forage legumes in north European livestock systems under both conventional and organic management

Changing from a conventional livestock production system, based on fertilized grass swards, to an organic management system requires the establishment of legume-based swards to replace the purchased fertilizer nitrogen. This paper reviews experimental-based research on both the comparative economics of legume-based systems and grass swards and also the economic advantage that forage legumes confer on organic systems. A methodology to determine the production costs and economic values of a variety of forage legume systems is outlined. The resultant methodology is then applied to experimental results from trials, conducted at a wide range of sites in northern Europe, to determine the comparative profitability of different legume-based systems of silage production under conventional management. The results indicate that potentially red clover (Trifolium pratense L.), and to a lesser extent white clover (Trifolium repens L.), and lucerne (alfalfa) (Medicago sativa L.), can produce higher profits per hectare than grass-based systems using high levels of nitrogen fertilizer. Galega (Galega orientalis Lam) and lotus (Lotus corniculatus L.) can, in certain circumstances, be economically competitive with fertilized grass swards, but would generally not be the forage legumes of first choice. From an economic standpoint, forage legumes are probably best grown in a mixture with grass. As some of the experimental sites involved organic treatments, the analysis has been extended to include an assessment of the comparative economics of organic systems of production based on forage legumes, relative to conventional grass-based systems. Thus, the third part of the paper is concerned with quantifying the economic advantage to organic systems conferred by forage legumes. The results indicate that, under careful management, their use for silage can produce higher profits per hectare for organic dairy systems than those obtained from conventional grass-based systems. While the relative performance of organic systems is strongly influenced by the price premium paid for organic milk, which has declined in recent years, not all the projected economic advantage of legume-based organic dairy systems is eroded by this trend. However, economic advantage is not enough to secure the widespread adoption of forage legumes. This will depend on technological developments and management practices which reduce the risks associated with both more difficult crop establishment and higher nitrate leaching of forage legumes as compared to grass swards.

Vegetable and Corn Yields in the United States, 1900-Present

-1 . The average yield for the 1990s was 7839 kg·ha -1 , 5 times the yield of the 1930s. A number of researchers have studied the basis for this increase by partitioning the contributions of improved genetics from those of improved management. Systematic studies performed by Duvick (1992) on corn hybrids grown from 1930 to 1989 in cen- tral Iowa demonstrated a linear increase in yield for the duration of this time period. An equivalent of 56% of the annual average gain in Iowa corn yields for this period was determined to be attributable to the ge net ic improvements of these hybrids (Duvick, 1984, 1992). It is clear from Duvick∑ s studies that much of the genetic change is represented by increased inputs and stress associated with high input intensive man age ment systems. Modern corn is much more resistant to drought stress associated with high population densities (30,000 plants/ha, 1930s; 80,000 plants/ha, 1980s) (Duvick, 1999). High levels of nitrogen fertilizer in creas es stalk lodging in grain crops. Modern corn is more resistant to stalk lodging than corn from the 1930s. High population den si ties also increase stalk lodging. Thus, in corn genetic changes were required for optimum use of increased inputs and higher population densities. In order to carry out comparative studies, seed of cultivars repre- senting different eras must be obtained, planted, and evaluated un der controlled conditions at a number of lo ca tion × year combinations. The experiment should include multiple production practices, re flect ing current management practices as well as older practices. Such studies have been con duct ed in a number of agronomic crops (soy bean (Glycine max L. Merrill), Specht and Williams, 1984; barley (Hordeum vulgare L.), Wycham and Rasmusson, 1983; sorghum (Sorghum bicolor L. Moench), Miller and Kebede, 1984), and in most cases large portions of the overall yield gain have been attributed to progress from plant breeding. However, Douches et al. (1996) found little influence of genetic improvement in the large increases in potato (Solanum tu- berosum L.) yields in the United States since the 1920s. Those workers found most of the gains from breeding programs during this period were associated with early maturity and improved tuber appearance. Thus, the primary reason yields increased was likely improvements in production practices.