Analysis of the trends of the cultivated area, agricultural production, and water resources in the past 50 years shows that focus of agricultural development has to be on intensification to cope with the rising demands for food of the growing population in Iran. This means more pressure on soil resources, which threatens sustainable production and food security. It also shows the key role of soil fertility and balanced soil fertilization, which is the main concern of the agricultural sector as well. In this paper, fertilizer recommendation and forecast are investigated as the first and the main steps of fertilizer system including recommendation, forecast, supply, allocation and consumption. Considering soil and plant nutrient criteria and fertility evaluation of some 20, 000 soil samples revealed that more than 50 percent of the cultivated soils suffer from the deficiencies of one or more nutrients.Furthermore, the low soil organic matter content is the main limitation factor of sustainable soil fertility and production. Among the four fertilizer recommendation approaches based on soil test, fertilizer recommendation in Iran is more based on thesufficiency range approach. Due to the lack of adequate data, the other approaches includingbuild up, maintenance, and cation balancemethods have been ignored, but should be considered in the future. Fertilizer recommendation trend shows a transition from the general and regional recommendation towards the soil test recommendation along with more attention to research and soil analysis. In addition to soil test as a base of fertilizer recommendations, other factors such as climate (drought, temperature), soil (salinity), plant (uptake efficiency) and agronomic management (rotation) should be considered in the fertilizer recommendations system. Fortunately, the first steps for integration of these factors are gathered inautomated fertilizer recommendation program which needs more complete investigations. Among the five main fertilizers forecasting models in Iran, fertilizer estimation is more based oncrop based model and has a generation trend due to more availability of soil and plant analysis data. This trend shows more fertilizer requirement in the future.However, it is necessary to distinguish between the total fertilizer requirement and its consumption at the farm. This means fertilizers consumption is not balanced in general, while balanced fertilization should be the main policy. There should be anational soil testing program in a way to include all stakeholders (private soil test lab, producers, etc) in fertilizer program. With the preparation of soil test infrastructure and facilitation of farmers' access to soil lab and appropriate fertilizer, balanced fertilization and, consequently, sustainable soil fertility, food security, and environmental protection could be achieved.

The variability of phosphorus concentration in soil solution as adsorption point of view by different minerals could be use for phosphorus recommendation. Identity of phosphorus adsorption on mineral surfaces could be studied by different equations, which their suitability depends on the soil characteristics and the aim of research. But the main concept is based on to equilibrate the soils with electrolyte solution containing different phosphorus concentration in a distinct time and temperature. In this study, three calcareous soil samples (with 7, 14 and 21 percentages CaCO3), fine grinded (<1mm diameter) were equilibrated with five concatenations (0, 12.5, 25, 50 and 75 mgrP/ml) which prepared from K2H2PO4 in 0.01 molar CaCl2. The linear types of Froundlich and Longmuir equations were fitted with high probability (p<0.01) and were used for interpretation phenomena by three soils. The Froundlich equation had higher correlation coefficient. The maximum adsorption values (b) of Longmuir equation for Karaj, Kordamir and Aderan soil series were 65.74, 74.2 and 75. 2, and the energy constant (k) were 2.95, 3.49 and 0.43, respectively. The samples were linear to concentration value (C) as high as 0.75, 0.73 and 0.29 mg/l for Karaj, Kordami, and Aderan soil series, respectively.

In order to evaluate the computerized fertilizer recommendation model developed by the Soil and Water Research Institute for wheat, an experiment was conducted in Golpaygan area designed in four treatments. T1= Control; T2= Computerized recommendation; T3= 30 percent less than T2; T4= 30 percent more than T2 + 150kg potassium sulfate (SOP). This trial was designed in randomized complete block with four replications in three different regions with two different water sources, in sodic/saline soil conditions. The trial was conducted in agricultural year 1998-99. The concentrations of N, P, and K in the first plot were 0.1 percent, 6.2 and 400 mg/kg. In the second plot the values were 0.1 percent, 6.0 and 430 mg/kg respectively, and in the third plot the values were 0.1 percent, 26.2 and 780 mg/kg respectively. Electrical conductivity for water in the first and the second plots was 4.54 and for third plot was7.36 dS/m. Analysis of treatments showed that fertilizer treatments had a significant difference with the control. Grain yield in T1 was 863 kg/ha and in T2, T3 and T4 were 3942, 2321 and 4418 kg/ha respectively. All treatments were significantly different from the control and the difference between T1, T2, T3 was significant (P=0.01) but the difference between T4 and T2 was not significant (P=0.05). The weight of 1000 grains difference between treatments and control was significant. It was 32.52 gr in T1, and in T2, T3, T4 were 46.36, 38.83 and 49.93 and was significant (P=0.05) between T2 and T4. Protein content was higher in treatments in comparison with the control and between T4 and control the difference was significant. Protein percentage in control was 12.6 and in T2, T3 and T4 were 13.45, 13.49 and 13.88 respectively. Nitrogen percentage in the straw was higher in treatments than control, but the difference was not significant. Nitrogen percentage in straw in the control was 0.30, and in T2, T3, and T4 were 0.37, 0.35, 0.44 respectively. Chloride, P, and K concentrations in grain were not significantly different between treatments and the control

The objective of this research was to study the effect of fertilizer management on the yield increase of crop plants. The extra amounts of applied fertilizers were studied by comparison between allocated, applied and recommended fertilizers’ amounts for: wheat, barley, corn and alfalfa with four replicates and the other data was gathered via questionnaires. Soil analysis of phosphorus, potassium and nitrogen amounts was performed in 20 fields and analysis of data was conducted base on complete randomized block design. Comparison of the averages was showed that there were significant differences between the amounts of allocated, applied and recommended fertilizers (P≤0.05). The average amounts of extra applied and extra distributed fertilizers were 382.9 and 150.6 Kg.ha-1 more than the recommended amounts, respectively. However, there was no significance increase in yield.12 and 28% of farmers used the fertilizers in the basis of recommended and allocated, respectively and 60% of them used more than recommended amounts. Excess fertilizer application due to improper management causes reduction of soil and water quality.

Fertilizer is known as an important factor in agricultural production since many years ago. Use of chemical fertilizers in Iran started more than 50 years ago and has grown during recent years. Nowadays, issues such as fertilizer quality, distribution, scientific recommendation, methods of application, environmental effects, and chemical residues in crops are very important concerns. Fortunately, attention to “fertilizer” as a subject in national laws and legislations has grown during recent years and, in contrast to earlier years when the focus was just on supply and distribution, nowadays, issues like quality controls and environmental effects are receiving attention as well. However, lack of a comprehensive national law and management system as a regulator of different fertilizer system parts is clear now. Assessment of fertilizer system including production, distribution, application, import and export, and related standards shows that “Comprehensive National Law”, “Institution Responsible for Fertilizer Management” and “National Quality Standards for Different Kinds of Fertilizers” are three important missing components in fertilizer management system.

Precise application of the N fertilizer rate is critical to achieve maximum yield. In major regions, empirical methods were used for determining N fertilizer requirement. These methods cannot take into account variation in management and environmental conditions on determining fertilizer requirement. Crop simulation models can provide an alternative means of determining the optimum crop N requirement under varied management and climatic conditions. In the present study for assessment of N fertilizing of wheat farms in Gorgan region, we conducted a survey on 95 wheat farms integrated with simulation experiment using CropSyst model. On-farm assessment showed that the amount of applied and recommended N fertilizer application varied between 45-175.5 and 67.5-146.3 kg ha-1, respectively. In addition, the amount of applied N fertilizer on 72 farms was more than recommended. Comparison of applied and recommended N fertilizer to optimum N fertilizer estimated by simulation model (171 kg ha-1) showed that the amount of applied N fertilizer on 93 farms and the amount of recommended N fertilizer on all farms were lower than optimum N fertilizer. This indicated that there was a gap between both applied and recommended fertilizer with optimum N fertilizer and this gap was more between recommended and optimum value. Therefore, it was concluded that the method of fertilizer recommendation on farms has not been effective and the current method of fertilizer recommendation should be revised for achieving the higher yield on farms.

The purpose of this study was to evaluate the effect of bacterial chemical integrated feeding system on yield and yield components of wheat phonological growth stages. Treatments included: Two levels of bio fertilizers B1: Seed inoculation with bio fertilizer, B2: Sterile inoculated seed, three levels of N fertilizer N1: Nitrogen fertilizer application 20% less than recommended, N2: Nitrogen fertilizer equal to recommended, N3: Nitrogen fertilizer application was 20% more than recommended in 4 replications in a completely randomized block design. The results showed that using B2N2 treatment, grain yield was 16. 14% and 16. 36% higher than B2N1 and B2N3, respectively. By applying B2N2 treatment, 1000-grain weight was higher than B2N1 and B2N3 as 11. 05% and 6. 92%, respectively. Grain yield was increased with simple nitrogen fertilizer treatment by fertilizer application 20% less than recommended at 12. 20% and by application of fertilizer by 20% higher than recommended by 16. 67% which was significant. The effect of bio fertilizer and nitrogen fertilizer treatments on bio farm inoculation and nitrogen application on sterile inoculation was quite noticeable. Therefore, bio farm fertilizer application and nitrogen fertilizer application are based on fertilizer recommendation to improve yield of wheat and its components. This highlights the importance of the bacterial chemical fusion system at different stages of wheat growth.

Soil tests play a very important role in management of nutrients in the field. Critical level of soil nutrient elements in a region is the basis of interpretation of the soil test for the same region. Therefore, these tests should be carried out in the soils of the target areas, so that the soil test could be used for fertilizer recommendation. Beans (Phaseolus vulgaris L. ) with high protein content are an important crop that is cultivated in Markazi province. Due to the lack of information on phosphorus critical level and regional calibration, this study was conducted on soil under bean cultivation in Markazi province. Twenty-three soil surface samples (0-30 cm) were selected with wide range of soil properties and phosphorus concentration (extracted with Olsen method) from the different locations of the province and were prepared for greenhouse cultivation. Bean plant responses were investigated by application of two levels of phosphorus (0 and 50 mg kg-1 soil as mono calcium phosphate) in greenhouse experiment. The study was conducted in factorial experiment as complete randomized design with three replications. At the end of vegetative period, the aboveground parts of plants were cut, and plant responses including, dry matter weight, phosphorus concentration, total phosphorus uptake, and relative yield were determined. Analysis of variance showed that the main effects and interaction of soil and phosphorus fertilizer were significant at 1% probability level for dry matter weight, phosphorus concentration and phosphorus uptake. The mean comparison of plant responses was significant as affected by phosphorus fertilizer consumption. By using Cate-Nelson graphic method, the critical level of phosphorus in soils was determined to be 13 mg kg-1. Dry matter showed positive significant correlation with available phosphorus and organic carbon. The total phosphorous uptake showed a positive significant correlation with available phosphorous concentration, electrical conductivity, sand and organic carbon content, and a negative significant correlation with clay content.

A five-years research project lasting from 1998 through 2002 was conducted in order to evaluate the process of optimizing fertilizer recommendations on wheat using comprehensive computer models. The potential yields for any region of the country was taken to be equal to the maximum yield figures obtained with actual research data gathered from field work as well as data obtained with maximum potential yield estimations. Based on our calculations, the most important soil and water production factors can be listed as the rate of water application, the salinity level of irrigation water, calcium carbonate equivalent (TNV), soil texture, and finally the level of soil salinity which can determine the expected crop yield. Measuring the effect of any of these variables on crop yields enables us to calculate the potential yield for that soil. It is, therefore, necessary to evaluate the potential yield for any field before we can make any fertilizer recommendations. The rate of nutrient requirement for any crop on any field location would be calculated after determining the concentrations of plant available nutrients by using tables on different soil nutrients in addition to estimating the potential yield. The computer model input data include soil analysis data, water analysis measurements, the name of province, town and then with pressing OK tab, output datas include fertilizer recommendations for macronutrients, micronutrients and organic materials, data on crop variety, data of planting and the rate of seeding which should appear on the monitor and be automatically stored in the information bank memory and could be viewed on the monitor and printed as needed. This computer program was written in Visual Basic with the objective of using research data in a single model so as to be able to find quantitative answers in a simple fashion. Of major importance is the fact that the program is mechanized as to include the use of suitable date of planting, rate of seeding, and soil amendments in addition to including soil parameters, organic contents, and plant varieties for every region on irrigated production.

Several methods have been proposed for recommendation of phosphorus fertilizers. Each of them only examines the concentration of phosphorus in the soil or plant, while none of them investigates the correlation between phosphorus concentrations in the soil and plant. In this study, a method called "integrated plant and soil system" (IPSS) is proposed to describe phosphorus fertilizer. In this system, for recommendation of phosphorus, the correlation between this element in soil and plant was used. For this purpose, 39 Washington Navel Orange orchards were selected in Jahrom region and from each orchard three trees were chosen. Samples were taken from soil and plants during two consecutive years and their phosphorus was measured. Orchards were divided into two categories, first group high-yield orchards and another includes all orchards. The correlation was run between soil properties and phosphorus of plant organs with the phosphorus of soil saturation extract samples. Factors were selected that shown significant correlation with the phosphorus of soil saturated extract, and multivariate regression was established between them. The results showed a significant correlation between phosphorus of plant organs and soil samples, and the highest correlation was observed between fruit phosphorus and phosphorus of soil saturation extract. Moreover, there was a significant correlation between phosphorus of plant organs, and the highest correlation was observed between fruit phosphorus with other plant organs. A equation was also obtained for each of the two orchard groups, these two equations can calculate the amount of phosphorus required for orange orchards.