شاخص برداشت نیتروژن

Optimum sowing date is very important and it is one of the important factors for maximizing yield production. Although chemical fertilizers provide plant nutrients faster, to increase the quality of products, especially medicinal and aromatic plants, the use of organic fertilizers is better. The purpose of this research was to Investigate the effect of planting date and different amounts of farmyard manure on nitrogen crop efficiency, nitrogen absorption efficiency, nitrogen utilization physiological efficiency, nitrogen harvesting index and seed yield The experiment was carried out in the form of split plots based on a completely randomized block design in three replications in the research farm Campus of Agriculture and Natural Resources, Razi University in 2021. Experimental treatments included farmyard manure as the main factor (0, 10, 20, and 30 ton ha-1) and sowing date (April 4, April 24, and May 14) as a sub factor. The results showed that sowing date, farmyard manure and their interaction had a significant effect on all evaluated traits. The increase in farmyard manure decreased nitrogen capture efficiency (NCE), nitrogen physiological efficiency (NUE), nitrogen agronomic efficiency (ANUE) and nitrogen harvesting index (NHI). By increasing farmyard manure application from 0 to 30 ton ha-1, NCE, ANUE, NUE and NHI decreased 50.23, 54.55, 73.16 and 61.65, respectively. Based on the results, the sowing date of April 4th, accompanied by the application of 30 ton ha-1 of farmyard manure, was the best treatment in this experiment.

There is an urgent need to increase per capita food production to compete with high population growth while maintaining environmental sustainability. Because nitrogen plays a vital role in food production for humans and livestock, nitrogen management is essential in food production. In most cropping systems, nitrogen management seems to be a major challenge due to its high mobility and natural tendency for losses from the soil-plant system to the environment. Soil organic carbon plays a key role in improving soil ecological conditions. Adding organic matter to the soil is an excellent tool for improving physical, chemical and biological conditions and is almost always desirable. Soil organic carbon stock of crop ecosystems may be increased by improving farming practices. The application of green manure, fertilizer and the return of crop straw into the soil are known as management operations to increase soil organic carbon. Fertilizers, especially nitrogen, increase crop yield, and organic carbon is returned to the soil through roots and debris, which in most cases leads to increased soil organic carbon.

This study was conducted with the aim of utilizing a set of improving farming practices in diverse cropping systems to improve nitrogen efficiency during two crop years. Farming practices including removal of summer fallow were used by importing three crops of mung bean, corn and wild rocket in rotation plus nitrogen supply levels factor. The crop rotation factor was applied in four levels of Fallow-wheat, mung bean-wheat, corn-wheat and wild rocket-wheat and the factor of nitrogen fertilizer (0, 180 and 360 kg.ha-1) in a randomized complete block design as factorial. Soil mineral nitrogen (nitrate and ammonium) were measured before sowing wheat and grain, straw and total plant nitrogen after harvest. Uptake efficiency, utilization efficiency, agronomic efficiency and nitrogen harvest index were calculated.

The results of combined analysis of variance showed that the crop rotation and nitrogen were significantly effective (ρ ≤ 0.01) on plant nitrogen, harvest index and nitrogen efficiency. Increasing nitrogen fertilizer up to 360 kg.ha-1 increased grain nitrogen, straw nitrogen, total plant nitrogen and also nitrogen harvest index. While the best uptake, utilization and agronomic efficiency of nitrogen was observed on the treatment without nitrogen fertilizer. Comparison of the means showed that the wild rocket-wheat crop rotation had the best result among all measured traits except utilization efficiency, while the utilization efficiency in the corn-wheat crop rotation showed the best performance. The results clearly show the effect of increasing organic carbon on nitrogen availability and grain nitrogen concentration as well as the role of cover crops and legume, in increasing access to nitrogen. The amount of grain nitrogen was directly affected by the amount of nitrogen fertilizer. The highest correlation coefficient was seen between agronomic and uptake efficiency (r = 0.96**). There was also a significant inverse relationship between nitrogen harvest index and the types of calculated efficiencies. The amount of uptake efficiency and agronomic efficiency in all crop rotations except corn-wheat in the second year improved compared to the first year. The highest increase in efficiency in the second year was related to the wild rocket-wheat crop rotation. In the conditions of 360 and 180 kg.ha-1 nitrogen fertilizer, the nitrogen harvest index increased in the second year compared to the first year. While in conditions without nitrogen fertilizer, nitrogen harvest index has a significant decrease. Therefore, at least in the short term, to increase the nitrogen harvest index, the minimum supply of nitrogen fertilizer should be used, even under improving crop management conditions such as green manure, removal of fallow and introduction of legumes in rotation and return of crop residues.

Continuous cropping, removal of fallow, use of cover crops and legume and preservation of residues led to increased carbon and nitrogen sequestration in soil and consequently increase biomass and nitrogen concentration in plant tissue. On the other hand, crop rotations that increased soil organic carbon and improved soil fertility quickly improved nitrogen efficiency and nitrogen harvest index.

Climate changs is one of the most important issues that has been observed in agriculture in recent decades and has limited production of crops. SSM-iLegum-Chickpea model was used to simulate the effect of climate change on evapotranspiration and leaf area index and growth indices of chickpea seed in Gonbad. First, meteorological data from the Dome Synoptic Meteorological Station from 1993 to 2017.The scenarios include increasing the temperature by two, four and six degrees, increasing the Co2 concentration by two times, and reducing rainfall by two percent, and a combination of the above scenarios, which total 9 scenarios. For the high temperature scenarios, the maximum and minimum daily temperature changes were added. Results of analysis of variance showed that in dry and irrigated conditions the effect of sowing date and climate change scenarios on all traits such as grain filling period, grain filling speed, evapotranspiration, leaf area index and total grain nitrogen except Harvest index nitrogen (NHI) was significant at 1% level in dryland conditions. But the interaction effect of planting date and climate change was only significant on evapotranspiration and leaf area index at 1% and NHI at 5% level. Duplication of concentrations of CO2 caused increasing about 6.2 in harvest index of nitrogen. Also, the best planting date for Gonbad city is the beginning of December in the simulation conducted for Gonbad.

This experiment has been performed to study the effect of seed sowing density and different amounts of nitrogen fertilizer application on the remobilization indices in wheat (Qaboos cultivar) in the field of Gonbad Kavous Agricultural and Natural Resources Research Station in two years (2018-19 and 2019-20) in three replications and as a split-plot in a randomized complete block design. The main plots include pure nitrogen at four levels, i.e., 0 (control), 46, 92, and 138 kg/ha of nitrogen from urea fertilizer source), and the subplots are planting density at six levels (150, 225, 300, 375, 450, and 525 seed/m2). The remobilization photosynthetic assimilate separately from leaves, main stem (without leaves), and seedless spike components are examined to study the process of photosynthetic material transfer to seed. Results show that there has been significant differences among planting density, nitrogen fertilizer, and interaction of planting density× fertilizer treatments in terms of grain nitrogen percentage and remobilization traits of wheat. The highest percentage of grain nitrogen (1.87%) has been obtained in the treatment of 138 kg/ha nitrogen and 450 seed/m2. In the first year, the highest remobilization from the plant is observed in the treatment of 92 kg/ha nitrogen and 375 seeds/m2 (0.528 gr/plant), and in the second year, in the control, the highest remobilization is observed in the planting density of 300 seeds/m2 (0.345 gr/plant), and then with increasing planting density, the remobilization from the plant is reduced.

Grain N content in barley plant is affected by N remobilization from vegetative organs to the grain during the grain filling period. The amount of N remobilization is negatively affected by the severe water stress after anthesis. Using of Azospirillum as a biofertilizer is a way for reduction the adversely effects of the severe water stress in the arid regions. Another way is increase the amount of soil organic matter (such as using of plant residues). Therefore, this study investigated the effects of wheat residues application and different N sources (biological and chemical) on N remobilization and grain N content of barley.

This research was conducted at the experimental farm of the Darab Agricultural College of Shiraz University. A split factorial experiment in a randomized complete block design with three replicates were carried out in 2017 - 2018 growing season. Treatments included: two levels of irrigation as the main plots [normal irrigation (IRN): irrigation based on the plant's water requirement up to the physiological maturity and another factor was deficit irrigation (IRDI): irrigation based on the plant's water requirement up to the anthesis stage (cutting of irrigation after anthesis)]. Also, sub plots were two levels of plant residues [1. without residue, 2. returning 30% of wheat residues to soil] and four fertilizer sources [N0, no nitrogen fertilizer (control); N100, 100 kg N ha-1; Bio + N50, Biofertilizer (Azospirillum brasilense) + 50 kg N ha-1 and Bio, Biofertilizer (Azospirillum brasilense)].

Application of N100 and Bio + N50 treatments significantly increased the N remobilization efficiency by 36% and 34%, respectively, as compared with the control (N0) under IRN. In contrast, under IRDI condition, all N sources decreased the N remobilization efficiency as compared with the control (N0). However, the amount of reduction in Bio + N50 and Bio treatments (10% and 11%, respectively) was lower than N100 (21%). The similar trend of N remobilization efficiency was observed for N harvest index in IRN and IRDI. Nitrogen harvest index showed a positive and linear relationship with N remobilization efficiency under both irrigation regimes. However, the justified variation of the N harvest index by N remobilization efficiency under IRDI was higher than (25%) the IRN conditions (R2 = 0.70 and R2 = 0.45). Also, Grain N content linearly increased with increasing N remobilization under both irrigation regimes. Application of wheat residues significantly reduced the N remobilization efficiency and grain N content in Bio + N50 and Bio treatments as compared to non-applied of residue. Also, there was no significant difference between with and without residue treatments in N remobilization efficiency and grain N content when N100 treatment was applied.

According to the environmental and economic considerations, integrated N fertilizer [Biofertilizer (Azospirillum brasilense) + 50 kg N ha-1] is recommended for normal irrigation conditions in order to maximum grain protein content achievement. In contrast, under cutting of irrigation after anthesis conditions, biofertilizer treatments (using of Azospirillum brasilense alone or using of it with integration to 50 kg N ha-1) reduced N remobilization efficiency as compared with control (N0). However, the decrement values were lower than the sole chemical N fertilizer (100 kg N ha-1). Therefore, in Southern Iran where water stress after anthesis is possible, biofertilizers is recommended. Also, using of wheat residues is not recommended for increasing N remobilization efficiency and consequently grain N content across over all irrigation and N regimes.

In order to investigate the N uptake and N utilization efficiency and nitrogen harvest index in corn and bean intercropping under the influence of tillage systems and residues of wheat an experiment was performed using split- split plots based on a randomized complete block design with three replications in agricultural research field of Shahrekord during growing season of 2016–2017. The tillage systems with three levels (conventional, minimum, and no tillage) and four levels of crop residue (0, 30, 60, and 90% of straw yield of wheat) and five intercropping patterns including corn monoculture, bean monoculture, corn and bean ratio with 2:2, 3:1 and 1:3 were considered as main, sub and sub-sub plots, respectively. The results showed that the highest nitrogen content in seed and biomass of both crops under conditions of use of 60% of plant residues, no- tillage systems and their monocultures. Agronomic use nitrogen efficiency in intercropping was lower than their monocultures. The highest N utilization efficiency was obtained in 3: 1 and 2: 2, indicating a clear superiority of intercropping than monoculture. Therefore, intercropping corn and bean can improve the nitrogen utilization efficiency. By decreasing nitrogen fertilizer application, it can play an important role in the long-term sustainability of agro-ecosystems production.

IntroductionSoybean is a member of leguminoseae family with average protein percentage of 40%, which needs a large amount of nitrogen fertilizer to get maximum yield. Using biofertilizers, beside chemical nitrogen fertilizers, can reduce proportion of chemical nitrogen demand without any undesirable effect on quantity and quality of its yield. Biological nitrogen fixation of soybean by Rhizobium japonicam can improve nitrogen use efficiency parameters beside its yield. This experiment was conducted with the aim of study the effect of different levels of nitrogen, bio-fertilizers and Nano-nitrogen on nitrogen use efficiency (NUE) and yield of soybean (Glycine max (L.) Merr.) cv. Williamz.
Material and MethodsA field experiment was conducted as a spilt plot in a randomized complete block design with three replications in 2013 at research center for agriculture and natural resources of Darab, Fars, Iran. Main factor was mineral nitrogen at three levels (zero, 75 and 150 kg N ha-1 ) and sub plot was nitrogen source at four levels (Rhizobium japonicum, nano-nitrogen, nitroxin and control). Rhizobium japonicum bacteria was inoculated in rate of 125 gr per 50 Kg seeds, nitroxin in rate of 0.5 L per 9 Kg seeds, and nano-nitrogen in rate of 10 L ha-1. The experimental plot dimensions were 2 x 4 m consisting of 4 rows of cultivated soybean 50 cm apart. The seeds were planted 5cm apart on each row. A furrow irrigation system was employed during experimental period. After the physiological maturity the experimental plots were harvested and yield, yield components, protein, protein yield, seed nitrogen content at ripening stage, nitrogen use efficiency (NUE), nitrogen utilization efficiency (NUTE), nitrogen uptake efficiency (NUE) and nitrogen harvest index (NHI) were measured.
Results and DiscussionThe results showed that the interaction of nitrogen and nitrogen source was significant for grain yield, harvest index, nitrogen percentage in the grain ripening phase, seed protein and protein yield. Mean comparison showed that the highest grain yield (2018 kg ha-1) obtained from application of 75 kg N ha-1 with Rhizobium application and the lowest grain yield (1476 kg ha-1) obtained from the no nitrogen fertilizer application. The highest seed protein percentage and seed protein yield observed in application of 150 kg N ha-1 with Rhizobium application. The highest nitrogen in the grain (1.51 %) was related to application of 75 kg ha-1 N with nano-nitrogen application. The highest nitrogen content of shoot in harvesting stage was achieved by integrated application of 75 kg ha-1 nitrogen and nano-fertilizer nitrogen. The highest nitrogen harvest index (NHI) (77.81 %) obtained from application 150 kg ha-1 N with nano-nitrogen application, maximum nitrogen use efficiency (NUE) (26.90 kg kg-1) was obtained from application of 75 kg N ha-1 and Rhizobium application and the minimum (12.66 kg kg-1) was obtained from application of 150 kg N ha-1 and Rhizobium. Generally, soybean production in Darab region had the best results with the use of 75 kg N ha-1 along with the Rhizobium japonicum application.
ConclusionsApplying of biofertilizers beside chemical nitrogen, could decrease chemical nitrogen use without any impact on qualitative and quantitative yield of soybean. According to the results of this study application of half of the recommended amount of nitrogen (75 kg N ha-1) and inoculation with Rhizobium japonicum bacteria (125 gr per 50 kg seeds) had the highest grain yield, harvest index, nitrogen use efficiency (NUE) and nitrogen harvest index (NHI). It seems that combined application of bacteria and chemical fertilizers can improve soybean performance and also reduce its chemical nitrogen demand. Our results suggested that, integrated application of 75 kg ha-1 nitrogen and Rhizobium can be suitable treatment to soybean production in Darab climatee.

IntroductionBetween oil seeds, from the quality, quantity and nutrition index point of view, canola has the top level . Because of the solubility of N fertilizers, the time of urea application, is very important and one of the main reasons of the reduction in N application efficiency is utilization of urea in an inappropriate time. By precisely foliar application of nitrogen, the efficiency of nitrogen transformation to the grain will be very high because in this method the leaf is considered the main organ of nitrogen uptake and a low amount of absorbed nitrogen was transferred to the root and entered the soil. The more division of N application in growth stages and in accordance with plant need and foliar application result in increasing nitrogen use efficiency. The delay in sowing will result in the reduction of yield and this is due to low LAI, and thus low radiation absorb in vegetable phase and shorter reproductive phase with high temperature in flowering and subsequent stages that result in low prolific silique and make disorder in transferring stored material to grain. In this experiment using N foliar application to decrease the adverse effect of delay in sowing is objective.
Materials and MethodsThe experiment was conducted in 2013-2014 in Ramin Agriculture and Natural Resource University of Khuzestan. Experiment was conducted as split plots in a randomized complete blocks design with three replications. In this experiment sowing date]optimum sowing (27 November), 17 December and late sowing (30 December) [were assigned to main plots and several time of N-foliar application with 5 percent density from urea (20 liter per ha), ]TO (control), T1 (foliar N application in rosette stage), T2 (foliar N application in budding stage), T3 (foliar N application in flowering stage)[ were placed in sub-plots in randomized way. Fertilizing was based on the results of soil examination. Therefore, 162 kg ha-1 of pure nitrogen (from resource urea) in the way of dusty application (1/3 after appearance of seedling on the soil, 1/3 in 3-4 leaves stage after thinning and 1/3 at the beginning of steam elongation) and 100 kg.ha-1 super phosphate triple in all plot was applied before planting. Each plot was consist of 8 planting line with 20 cm apart from each other and 4 m length. The data were analyzed by using SAS and mean comparison of data based on LSD test in 5% probably level.
Results and DiscussionLate sowing date and nitrogen foliar have significant effect on the yield and efficiency and uptake index of nitrogen. With delay in sowing because the flowering and silique formation stage faced with the heat tension, the vegetative phase, production of photosynthesis matter and growth all treatment like: yield, oil yield, biological yield, oil seed percent, nitrogen harvest index, nitrogen use efficiency, nitrogen utilization of agronomy efficiency and amount of nitrogen uptake, were decrease. But it should be pointed out that with delay in sowing the percentage of nitrogen seed and nitrogen of all bushes was increased.
The highest yield with mean of 3406.6 kg.ha-1 was relevant to first sowing date and least yield with mean 1803 and 1499.1 kg.ha-1 was achieved of second and third sowing date, respectively. In foliar treatment the highest yield was obtained from N foliar in budding and flowering stages and the least yield was obtained from control treatment.
Foliar in budding and flowering stages by increasing the green surfaces of plant, more benefit of sun radiation, increasing in photosynthetic activity were increase and in this way the seed yield and oil yield were increase. As well nitrogen harvest index was increased with increasing of assigned nitrogen to silique in canola and the reduction in wasting of nitrogen will be increased by consume it in appropriate time. With nitrogen foliar application because of availability of nitrogen in appropriate amount and adequate utilization of plant of nitrogen, caused to increase the nitrogen utilization of agronomy efficiency and nitrogen uptake amount.
ConclusionsThe results of this experiment showed that with delay in sowing the flowering and grain formation stages were faced to heat tension and can result in reduction in all treatment. The nitrogen foliar in heat stress caused an increase in seed yield, oil yield, dry mater, nitrogen harvest index, nitrogen utilization of agronomy efficiency and amount of nitrogen uptake. As the result, first sowing date and N foliar application in budding and flowering stages were best treatment in this experiment.

To evaluate nitrogen uptake, nitrogen uptake efficiency, nitrogen use efficiency and nitrogen harvest index of wheat (Triticum aestivum L.) affected by different tillage systems and wheat residue application, an experiment was conducted as a split block experiment in a randomized complete block design with three replications at Ferdowsi University of Mashhad, Iran, during 2013-2014 growing season. Four different tillage systems (disk, mouldboard plough disk, sweep plough disk and chisel plough disk) were considered as vertical factor and five different crop residue applications (0, 25, 50, 75 and 100% wheat residue) as horizontal factor. The results showed that lowest (2.58%) and highest (2.77%) seed nitrogen percentage were obtained from disk and chisel plough disk, respectively. Also, the highest nitrogen uptake and use efficiency (60.67% and 17.25 g seed/g soil) were obtained from chisel plough disk treatment. The results indicated that seed nitrogen percentage, nitrogen uptake and use efficiency significantly increased with increasing the levels of wheat residue, so that application of 75% wheat residue increased nitrogen uptake to 62.2% compared with control treatment. Regarding to the results of this study, it seems that application of wheat residue along with reduced tillage as an ecological approach can be recommended in arid and semi-arid regions of Iran to increase nitrogen uptake and use efficiency.

There are about 160 species in Brassica genus, which are mostly annuals and biennials. The plants in this genus have potential for fodder uses. The progress in plant breeding science has produced new crop varieties for oil and forage usages. Perko varieties are derived from crosses between tetraploid plants of winter rapeseed (Brassica napus L.Var. napus) and Chinese cabbage (Brassica campestris L. var. sensulato). The new plants are superior to their parents from various aspects. Buko varieties are new amphiploid plants obtained by crossing between tetraploid winter rapeseed, Chinese cabbage and turnips (Brassica campestris L. var. Rapa). Oilseed radish with scientific name (Raphanus sativus L.) is a genus of the Brassica and consumption, oil, green manure, feed and fodder (24). This plant in many countries, including Canada, is cultivated in gardens as cover crop. Oilseed radish grows fast in the cool seasons. Ramtil (Guizotia abyssinica) belongs to the Compositae family, Phasilia (Phaceli atanacetifolia L.) belongs to Boraginaceae family and clover is from Fabaceae family that is grown for feeding purposes.

A field experiment was conducted from 2011 to 2012 in the Karezan region of Ilam, Iran (42º33′N, 33º46′E) on a silty-clay with low organic carbon (1.26%) and slightly alkaline soil (pH=7.9). This site is characterized as temperate climate with 370 mm annual precipitation. The experiment was arranged in a split plot based on randomized complete block design with four replications. The main plots consisted of 6 pre-sowing plant treatments (control, Perko PVH, Buko, Clover and Oilseed radish and combination of three plants Ramtil, Phaselia andclover), and sub plots covered four N fertilizer rates including no fertilizer N (Control), 50% lower than recommended N rate, recommended N rate and 50% more than recommended N rate. Winter wheat (cv. Pishtaz) was sown on mid-November with the row spacing of 15 cm and a seeding rate of 200 kg ha-1. Soil samples were collected after harvest of each crop from 0 to 30 cm and 31 to 60 cm soil depths using a soil auger. Wheat grain yield (according to 14% moisture) obtained by harvesting the central area of 3 in 10 m in each plot. Yield components were determined from two randomly selected areas (2m2) within each plot. Plant samples collected at harvest were separated into grain and straw and oven-dried at 60˚C for 72hr. Biomass and grain sub samples analyzed for total N content using a micro-Kjeldahl digestion with sulfuric acid. The terminology of N efficiency parameters was considered according to Delogu et al, (11) and Lopez-Bellido & Lopez-Bellido, (22), Rahimizadeh et al. (30), Limon-Ortega et al. (20) methods.

The results showed that there were highly significant differences (P ≤ 0.01) in forage yield. There were also significant differences (P ≤ 0.05) in total dry weight, protein content and protein yield between treatments. Perko varieties produced higher fresh and dry matter yield with 69,586 (kg ha-1) and 7147 (kg ha-1), respectively compared to other varieties. Buko varieties showed greater protein percentage with 23.36 compared to the rest of the varieties. The highest and lowest grain yield, with 8345, and 4491 (kg ha-1) were obtained for Buko; wheat rotation and fallow, wheat rotation, respectively. The highest and lowest nitrogen uptake was obtained for Buko; wheat and clover, wheat rotation, respectively. The differences between the rotations were significant for various agronomic nitrogen efficiency. The rotation of oilseed radish and wheat showed greater nitrogen economic performance with 36.20 kg ha-1. By increasing nitrogen rate agronomic performance decreased with the exception in fallow- wheat. Physiological efficiency of nitrogen in fallow-wheat rotation was more than 39 (kg kg-1) of nitrogen. The maximum efficiency of nitrogen recovery was obtained for oilseed radish: wheat and Perko PVH; wheat rotations with 45% and 36%, respectively. The highest nitrogen harvest index was observed in Buko; wheat rotation: (86.5%), and Perko: wheat (85%) and the lowest nitrogen harvest index was in fallow; wheat (79.28%).

The results showed that Perko; wheat and Buko; wheat rotations due to the higher economic performance in the region were appropriate rotations and were recommended for the study area.

The effects of irrigation levels and high corm density on replacement corms behavior and nitrogen uptake of saffron (Crocus sativus L.) were studied in a field experiment as split-plot based on a randomized complete block design with three replications at Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, during the years of 2012 and 2013. The irrigation levels of saffron based on water requirement (50, 70 and 100 %) and high corm density (50, 100, 200 and 300 corms per m2) were allocated to the main and sub plots, respectively. Based on the results, the lowest nitrogen content in replacement corm and aerial part of saffron (6.02 and 5.62 gm-2, respectively) were observed by sowing 50 corms per m2 + 50 % irrigation. In both years, nitrogen uptake efficiency, nitrogen use efficiency and nitrogen harvest index of saffron was significantly decreased by increasing the corm planting density. In the second year, nitrogen uptake efficiency, nitrogen use efficiency and nitrogen harvest index were more than the first year. It seems that higher planting densities, which named dense corm planting, can be considered as an alternative approach for increasing nitrogen use efficiency in saffron.

Nitrogen is one of the most limiting nutrients for cereal production in many parts of Iran. The effects of crop residue incorporation [0 (control), 25 and 50% of wheat (Triticum aestivum L.)] and nitrogen (N) levels (0, 150, and 300 kg ha-1) on corn (Zea mays L.) grain yield and nitrogen use efficiency were investigated at Agricultural Research Station, Shiraz University, Shiraz, Iran for two years (2009-2010). The experiments were carried out as a split plot based on randomized complete blocks design with three replications. The results showed that with increasing nitrogen fertilizer (from 150 to 300 kg ha-1) and crop residues (from 25 to 50%), RNE (Recovery N Efficiency) and ANE (Agronomic N Efficiency) were reduced. Application of nitrogen more than 150 kg ha-1 increased the amount of nitrogen loss from 69 to 121 kg ha-1. There was a liner relationship between the amounts of nitrogen higher than 150 kg ha-1, and the NHI (Nitrogen Harvest Index), but adding more than 50 percent of crop residues caused no significant difference in the NHI. The maximum grain yield was obtained in plants treated with 300 kg N ha-1 and 25 percent of crop residues incorporation. According to results, the use of 25% of crop residue and 150 kg N ha-1 due to acceptable yield, reduce nitrogen loss and increase the efficiency of nitrogen better than other treatments.

Effects of nitrogen fertilizer levels on Agronomic Efficiency (Ea), Physiological Efficiency (Ep), and Recovery Efficiency (Er), in rice (Oryza sativa L.) Cv. Khazar was investigated in a RCBD of three replications in a sandy soil in Guilan province, Iran in 2003. This study compared the effects of six N rates, namely: control (no N fertilizer), 40 (Basal), 40+40 (Basal + Midtillering), 40+20+20 (Basal + Midtillering + Panicle initiation), 60+60 (Basal + Midtillering) and 60+30+30 (Basal + Midtillering + Panicle initiation) Kg/ha in the form of urea. Nitrogen contents in shoot and in rice grain were determined at the end of plant growth and physiological maturity. Results indicated that grain yield in triple split application treatments sixth and fourth (4832, 4668 kg/ha) were significantly higher than those in the rest of the treatments. The highest N uptake was observed in sixth treatment (146.9 kg/ha), which was significantly higher than in the others. The highest Ea, Ep and Er were observed in the fourth treatment (20.1, 30.1 and 66.9% respectively). Ea and Er were significantly higher in the fourth treatment than in the others, but Ep significantly differed only in the second treatment. There were no significant differences observed among treatments in Nitrogen Harvest Index (NHI), the highest NHI being related to the forth treatment (0.44). Grain yield was not significant in the fourth treatment in comparison with that in the sixth one, but the higher Ea, Ep and Er may lead to an economization of N fertilizer application and as well to its less leaching in the sandy soil. The fourth treatment was finally decided as the best treatment for rice, Cv. Khazar throughout the whole experiment.