Fertilizer Recommendations For Crops Research Articles

Determination of Critical Limit of Zinc for Lentil (Lens culinaris L.) in Diverse Soils under Intensive Cropping Systems

Determination of the critical limit (CL) for nutritionally essential zinc (Zn) is very important in developing fertilizer recommendations for crops and soils. However, the CL of Zn for the lentil crop has not been determined yet in Bangladesh, leading to the use of a fertilizer rate for the crop estimated on the basis of old critical limit generalised for all crops. A study was conducted in the Greenhouse facilities of the Soil Science Division of BARI, Gazipur, from October to April (Rabi season) of 2018/2019 and 2019/2020, to determine Zinc CL for soils and lentil crop in soils collected at twenty locations encompassing the six Agro-Ecological Zones (AEZs) of Bangladesh. For extraction of available Zn concentrations from soils and lentil biomass, a diethylene triamine penta acetic acid (DTPA) (0.005 M) solution was used. The DTPA-extractable Zn (mg kg-1) in the soils were from 0.43 to 4.10 and from 0.52 to 4.20 in 2018/2019 and 2019/2020, respectively. In all seasons, accessible Zn had negative but substantial correlations with soil pH, soil P, Ca, and Mg in available forms, but the association between available Zn and lentil dry matter was positive and significant (DM). Soil Zn had also a positive significant correlation with Zn concentration of lentil tissue Zn (0.501**). In 2018-2019 and 2019-2020, the CL of EDTA-extractable Zn was determined to be 0.75 mg kg-1 and 0.68 mg kg-1 in soils for lentil crop (0.72 mg kg-1 on an average), respectively, while it was 48.6 mg kg-1 for lentil tissue. The revised CL can be used for fertilizer recommendation for the lentil crop in the entire Gangetic Plains and other Agro-Ecological Zones of Bangladesh. Keywords: Pulse crop, Nutrient management, Micronutrient, Dryland crop, Sustainable agriculture

Multi-stage fertilizer recommendation for spring maize at the field scale based on narrowband vegetation indices

Crop fertilizer recommendations that are site-specific and can be adjusted in multiple growth stages can result in improved nutrient management, fertilizer use efficiency, and grain yield. There are considerable challenges to collecting a large number of soil and crop samples using the traditional methods, so a modern approach to developing fertilizer recommendations is urgently needed. In this study, we used the topdressing recommendation method based on unmanned aerial vehicle-based hyperspectral images and conducted a long-term nitrogen–phosphorus–potassium (NPK) combined fertilizer experiment in a spring maize cropping system. The hyperspectral imagery was acquired at multiple critical stages (jointing, silking, and maturity) in the experimental field containing 120 microplots during 2019–2020. The leaf nitrogen content (LNC) and yield measurement data for each microplot were also collected in multiple stages. Ten narrowband vegetation indices (VIs) were derived from the hyperspectral imagery as effective indicators for the estimation of the crop N status and grain yield. To develop topdressing recommendations for multiple stages, first, the optimal NPK fertilizer amounts, which were applied as the total fertilizer requirement to achieve the highest yield, were obtained. Second, the thresholds of the narrowband VIs, which justify if topdressing N fertilizer is needed, were calculated using the regression model established based on the relative yield and VIs. Finally, the N fertilizer amounts already applied in the jointing and silking stages were obtained based on the response of the narrowband VIs to the N fertilizer amounts. The results reveal that the optimal amount of N fertilizer is 180 kg ha−1, and the grain yield can be improved by using a combination of P and K fertilizers. Five VIs were significantly correlated with both the LNC and yield in the jointing and silking stages, and the thresholds of these VIs, below which topdressing fertilizer is needed, were identified at 95% of relative yield. The five VIs all presented high fitting accuracies with the amount of N fertilizer applied. However, there were noticeable differences in the sensitivities of the VIs in the jointing and silking stages. Therefore, we developed a cost-effective approach and provide multi-stage fertilizer recommendations at the field scale for the spring maize cropping system. This method can also benefit other precision agriculture applications if incorporated with remote sensing techniques.

Verification of phosphorus critical level for bread wheat (Triticum aestivum L.) in Kofole District of West Arsi Zone, Oromia, Ethiopia

Verification of phosphorus critical level for bread wheat was conducted in Kofole District in 2019 cropping season with the objectives to verify phosphorus critical (Pc) level and determined during soil test crop response based phosphorus fertilizer calibration and to create awareness on soil test crop response based fertilizer recommendation. Composite soil samples at the depth of 0-20 cm in the zigzag method were collected from 10 farmers’ fields for Eutric Vertisols. Likewise, soil samples analyses were made to identify available P in the level of the required phosphorus in the select crop fields for the actual experiment. The treatments included (1) soil test based phosphorus calibration result; (2) farmers’ practice in the area which was assessed by the surrounding farmers’ and (3) no fertilizer application (control) and each treatment was planted on 10*10m experimental plot & the design was randomized complete block design replicated over farmers. Bread wheat, Ogolcho variety, was used with seed rate of 150 kg ha-1and other cultural practices such as weed and rust management were used from which had been recommended for the area. The partial budget analysis showed that the highest net income (71630.48 ETB) was from the soil test based recommended and the lowest net benefit (44378.55 Birr ha-1) was obtained from control treatment with a marginal rate of return (653.38%) which is greater than the minimum rate of return (MRR) 100%. The result showed that the average grain yield of 4745 kg ha-1 was obtained from the application of soil test based phosphorus calibration (Pc and Pf) followed by blanket recommendation (3853 kg ha-1) and 2778 kg ha-1 for the control treatment. The recommended N rate, 69 kg N ha-1 with soil test based phosphorus critical level gave a 58.54% grain yield advantage over the control. In general, soil test and crop response based fertilizer recommendation for crops increases crop yields through the application of adequate nutrient rates for the identified soil nutrient deficiencies in specific locations.

Development of a soil test correlation and calibration database for the USA

AbstractAs part of the Fertilizer Recommendation Support Tool (FRST) project, the FRST database was developed to consolidate and preserve U.S. soil test correlation and calibration data. Legacy phosphorus (P) and potassium (K) soil test data that met a minimum requirement were included in the database. The FRST database initially included over 1,200 individual trials from a range of years, cropping systems, geographic regions, and management practices. The FRST database is being migrated from a Microsoft Excel spreadsheet to a relational database format housed within the USDA‐ARS Agricultural Collaborative Research Outcomes System (AgCROS) to be accessed via the online FRST decision support tool. Data will be continually added to the FRST database through an online submission form following peer review by the FRST team. The FRST database and associated decision support tool will aid researchers, extension associates, consultants, and farmers in improving fertilizer recommendations for crops across the United States.

Science-based decision support for formulating crop fertilizer recommendations in sub-Saharan Africa

In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha−1 in Nigeria, 2.3, 0.9 and 0.2 t ha−1 in Ethiopia, and 1.5, 0.8 and 0.2 t ha−1 in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg−1 N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha−1 and K by 24 and 38 kg ha−1 than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha−1) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg−1, respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg−1). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha−1 than the blanket recommendations, but maize yield (6 t ha−1) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers.

Calibration of Mehlich-3 with Bray P1 and Ammonium Acetate in the Tri-State Region of Ohio, Indiana and Michigan

ABSTRACT Field crop fertilizer recommendations for Ohio, Indiana and Michigan are currently based on the Bray P1 extractant for phosphorus (P) and the ammonium acetate extractant (AA) for base cations. The fertilizer recommendations in this Tri-State region are currently being revised and will use the Mehlich-3 soil test extractant as the new basis for P and potassium (K) fertilizer recommendations. The goal of this study was to document the relationships between Mehlich-3, Bray P1, and AA soil test extractants and to provide a comprehensive review of these relationships published in the literature. Soil samples (n = 2,659) were collected across Ohio and Indiana from a diverse range of fields and analyzed for Mehlich-3, Bray P1 and AA extractable nutrients for P, K, calcium (Ca), and magnesium (Mg). Mehlich-3 P values were highly related to, but 35% greater than Bray P1 values. Mehlich-3 values were highly related to AA values, but 14% greater than AA-K, 13% greater than AA-Ca and 20% greater than AA-Mg. Our results are largely consistent with a comprehensively compiled literature review that indicates Mehlich-3 is an efficient and suitable soil test extractant for assessing extractable nutrient levels in the Tri-State region of Ohio, Indiana and Michigan.

Validation of Soil‐Test‐Based Phosphorus and Potassium Fertilizer Recommendations for Irrigated Soybean

Core Ideas The most common soil‐test‐based fertilization recommendation error is a false positive. Surface soil sample P and K concentrations are qualitative indicators of subsoil P and K concentrations. The R2‐stage, leaflet‐K concentration of irrigated soybean is an accurate indicator of yield responsiveness to K fertilization. Soil testing is the best available technology for making crop fertilizer recommendations, and precision agriculture has increased the demand for soil‐testing. Our primary research objectives were to validate the accuracy of soil‐test P (STP) and K (STK) availability (Mehlich‐3) and trifoliolate leaflet‐P and leaflet‐K concentration interpretations for predicting irrigated‐soybean [Glycine max (L.) Merr.] yield response to P and K fertilization at 22 site‐years. Each trial contained six treatments involving two P rates and four K rates including a no fertilizer‐P or ‐K control and the soil‐test recommendation. Yield and tissue nutrient concentration responses were assessed at three significance levels (p ≤ 0.05, p ≤ 0.10, or p ≤ 0.25) and identified as correct or incorrect according to the response predicted by soil‐test recommendations. The accuracy of soil and tissue analyses to predict the correct plant response to fertilization increased as the significance level moved from conservative (p ≤ 0.05) to liberal (p ≤ 0.25). Mehlich‐3 STP accurately identified soils that did not respond to fertilizer P and had an overall accuracy of 40 (p ≤ 0.05) to 48% (p ≤ 0.25) in predicting yield response to fertilization. Existing STK interpretations were 72 (p ≤ 0.05) to 82% (p ≤ 0.25) accurate. Critical leaflet‐K concentrations accurately identified soybean response to K fertilization at 46 (p ≤ 0.05) to 60% (p ≤ 0.25) of the sites. Interpretation errors were most common in the very low and low STP levels, low and medium STK levels, and the low tissue‐K level. The accuracy of the soil and tissue testing and their interpretation process were reasonably accurate for K but substantial improvements are needed for P.

Soybean Yield Response to Phosphorus Fertilization in an Oxisol under Long‐Term No‐Till Management

Core Ideas Plant available P extraction methods are compared The P accumulation in a long‐term NT system depends on P application rates Soil test is a good guide for fertilization to achieve optimum yields and minimum P buildup in the soil P content in soybean leaf samples is an indicator of soybean yield Phosphorus (P) fertilizer recommendations for crops must be improved to optimize crop yields and minimize the environmental impact of P. We evaluated the effects of continuous annual fertilization (double crops) on soil‐P availability by Mehlich‐1 (PM‐1) and resin (Presin), plant uptake, P responsive concentrations in the soil and soybean trifolioliate leaflets and the yields of two soybean (Glycine max L.) cultivars (BRS1010 and BRS1003) grown in a Brazilian Oxisol under 20 yr of no‐till (NT) management. Four treatments representing a combination of annual P rates (0, 20, 40, and 50 kg P ha–1) with a fixed K rate (40 kg ha–1) were evaluated. Resin‐extractable P was highly correlated with PM‐1 (0.86, p < 0.05) but Presin was nearly 2.5 times as much as PM‐1. The soil extractable P was linearly correlated with P contents in trifoliolate leaflets with r of 0.72 and 0.66 (both at p < 0.05) for PM‐1 and Presin, respectively. Maximum responsive concentrations of soil PM‐1 and Presin for the year studied were in the range of 13 ± 2.2 to 20 ± 5.7 and 30 ± 5 to 59 ± 19.2 mg P dm–3, respectively. Soybean yields increased 29% as the rates of annual‐P rate increased from 0 to 20 kg ha–1 and additional P application did not further improve yields. The trifoliolate leaflet P concentrations of both cultivars were correlated (r = 0.66, p < 0.05) with soybean yields. The maximum responsive concentration of P in the soybean trifoliolate was 2.8 ± 1.9 to 5.4 ± 2.8 g kg–1 at R2 stage. Our results confirm that soil test for plant available P and plant tissue test are important to guide P fertilizer recommendations.

English

Micronutrients are important for crop growth, production and their deficiency and toxicity affect crop yield. However, the up dated information about their status and spatial distribution in Ethiopian soils is scarce. Therefore, fertilizer recommendation for crops in the country has until recently focused on nitrogen and phosphorus macronutrients only. But many studies have revealed the deficiency of some micronutrients in soils of different parts of Ethiopia. To narrow this gap, this study was conducted in Kedida Gamela, Kecha Bira and Damboya districts of Kambata Tambaro (KT) Zone, Southern Ethiopia, through assessing and mapping the status and spatial distribution of micronutrients. The micronutrients were extracted by using Mehlich-III multi-nutrient extraction method and their concentrations were measured by using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The fertility maps and predication were prepared by co-Kriging method using Arc map 10.0 tools and the status of Melich-III extractable iron (Fe), Zinc (Zn), boron (B), copper (Cu) and molybdenum (Mo) were indicated on the map. The extracted Fe ranged from 50.04 to 209.72 mg/kg, 60.08 to 240 mg/kg and 46.84 to 412.23 mg/kg in Kedida Gamela, Kecha Bira and Damboya districts soils, respectively. Zn ranged from 1.3 to 28 mg/kg, 0.9 to 47 mg/kg and 1.0 to 39 mg/kg for Kedida Gamela, Kecha Bira and Damboya districts, respectively. The calculated manganese activity index (MnAI) indicated that Mn is in excess and even toxic. B ranged from 0.02 to 1.83 mg/kg, 0.4 to 1.44 mg/kg and 0.06 to 2.03 mg/kg in soils of Kedida Gamela, Kecha Bira and Damboya woredas, respectively indicating that most of soils were deficient in B. Cu ranged from 0.6 to 2.9 mg/kg, 0.5-1.44 mg/kg and 0.8 to 3.4 mg/kg in Kedida Gamela, Kecha Bira and Damboya districts indicating its status fall between low and optimum category. Mo ranged from 2.21 to 18.71 mg/kg in the soils of the study area indicating that all soils were sufficient in Mo content. The means of all micronutrients except B showed significant differences among districts and showed moderate spatial dependences. The range of semivariogram for all studied micronutrients was greater than the average sampling distance indicating that it was adequate enough to catch spatial variability of them. In order to strengthen this result, plant sample analysis and calibration of micronutrients with plant response are recommended. Key words: Boron, Copper, Iron, Kriging, Manganese, Mehlich-III, Molybdenum, Zinc and spatial dependency.

Rapid and Inexpensive Steam Distillation Method for Routine Analysis of Inorganic Nitrogen in Alkaline Calcareous Soils

Determination of inorganic nitrogen (N) in soil is important in making N fertilizer recommendations for crops. To find a rapid, reliable, and economical method for the estimation of inorganic N in alkaline calcareous soils of Pakistan, three steam distillation methods were compared using soils varying in ammonium (NH4) and nitrate (NO3) N contents and other physicochemical properties. In the standard method, the soil sample is shaken with 2 N potassium chloride (KCl) for 1 h, and the extract is then analyzed by steam distillation. In the other two methods, the soil sample is distilled directly with either 2 N KCl or distilled/deionized water. Based on the results of the present work, a method that involves steam distillation with only distilled/deionized water and that requires half the quantity of magnesium oxide (MgO) of the standard method has been proposed, as all the three methods yielded identical results for NH4- and NO3-N contents. Being economical, the proposed method for inorganic N estimation by direct distillation of soil with distilled/deionized water deserves consideration for adoption by soil-testing laboratories.

Variability of the Illinois Soil Nitrogen Test across Time and Sampling Depth

There is potential for using the Illinois soil nitrogen test (ISNT) to improve N fertilizer recommendations for crops in the southeastern United States. The ISNT has been previously calibrated to predict N rates for corn (Zea mays L.) in North Carolina. This study evaluated the effects of sampling time, sampling depth, crop rotation, and fertilizer application on soil ISNT‐N during a 2‐yr period in the humid Coastal Plain and Piedmont regions of North Carolina. Ten sites were repeatedly sampled at 0‐ to 10‐, 10‐ to 20‐, and 20‐ to 30‐cm depths in fall, mid‐winter, and spring between October 2006 and May 2007. Illinois soil nitrogen test N, KCl‐extractable soil NO3–N and NH4–N, and soil organic matter (SOM) derived by loss‐on‐ignition (LOI) were evaluated at each sampling. Temporal changes in these soil parameters were evaluated for various crop rotations and N fertilizer applications. Soil ISNT‐N decreased with depth and showed significant variation with time at all three depths at all sites. Soil ISNT‐N was influenced by crop rotation and tillage but was not significantly affected by N fertilizer applications. Considering all sites together, ISNT‐N was well correlated with LOI; however, ISNT‐N was not correlated with LOI across time within sites. This suggests that the ISNT measured a fraction of SOM that behaved somewhat independently with time.

Boron extraction and vertical mobility in Paraná State oxisol, Brazil

The deficiency or excess of micronutrients has been determined by analyses of soil and plant tissue. In Brazil, the lack of studies that would define and standardize extraction and determination methods, as well as lack of correlation and calibration studies, makes it difficult to establish limits of concentration classes for analysis interpretation and fertilizer recommendations for crops. A specific extractor for soil analysis is sometimes chosen due to the ease of use in the laboratory and not in view of its efficiency in determining a bioavailable nutrient. The objectives of this study were to: (a) evaluate B concentrations in the soil as related to the fertilizer rate, soil depth and extractor; (b) verify the nutrient movement in the soil profile; (c) evaluate efficiency of Hot Water, Mehlich-1 and Mehlich-3 as available B extractors, using sunflower as test plant. The experimental design consisted of complete randomized blocks with four replications and treatments of five B rates (0, 2, 4, 6, and 8 kg ha-1) applied to the soil surface and evaluated at six depths (0-0.05, 0.05-0.10, 0.10-0.15, 0.15-0.20, 0.20-0.30, and 0.30-0.40 m). Boron concentrations in the soil extracted by Hot Water, Mehlich-1 and Mehlich-3 extractors increased linearly in relation to B rates at all depths evaluated, indicating B mobility in the profile. The extractors had different B extraction capacities, but were all efficient to evaluate bioavailability of the nutrient to sunflower. Mehlich-1 and Mehlich-3 can therefore be used to analyze B as well as Hot Water.

Development of Standardized Fertilizer Recommendations for Corn Grown in the Mid‐Atlantic Region of the United States

Crop fertilizer recommendations often differ between soil test laboratories operating within a given physiographic region, due to differences in chemical method used, laboratory techniques, soil test interpretation, and philosophy of making recommendations. In 1998, the Mid‐Atlantic Soil Testing and Plant Analysis Work Group, comprised of representatives from government (university/state) and commercial/industrial laboratories, evaluated differences in corn N, P, and K fertilizer recommendations in an effort to achieve more uniformity. For P and K, comparisons were made for four popular extractants at key strategic soil test levels. These levels were 1) the “zero” extractable nutrient level to indicate the maximum amount of fertilizer recommended by each laboratory, 2) the soil test level of no further crop response to applied fertilizer (optimum/maximum yield) to indicate the maintenance fertilizer rate each laboratory was using, and 3) the soil test level above which no further fertilizer would be recommended. The extractable nutrient values each laboratory was using at each strategic soil test level were compared, and then a standard set of strategic soil test levels and fertilizer recommendations were developed. Regarding N recommendations, a range in application rates was selected for an appropriate target yield applicable to soils in the region. These recommendations were designed for gradual implementation by the laboratories in the work group.

RATIONALE OF THE ECONOMY OF SOIL TESTING

Probably the cheapest and most widely used chemical analysis employed in agriculture, soil testing is often not properly appreciated for the advantages it has for economically sound fertilizer recommendation for crops. In fact, soil testing is not only useful, but it becomes indispensable for this purpose, considering that it is used to determine unfavorable soil reaction and nutrient deficiencies and excesses that affect plant growth. To demonstrate how soil analysis and the economy of fertilizer use are interrelated, a quadratic model was used to show the magnitude of economic returns under different conditions, using soil analysis as starting point. The parameters used in the quadratic response model used were the sufficiency index of a nutrient obtained by soil analysis, the expected or maximum yield, and the nutrient rate to achieve this yield. Using the sufficiency index of the nutrient in the soil, the cost of the nutrient unit, and the value of the crop unit as inputs for the model, profits and return to investment ratios were calculated for several conditions, covering the range of yield levels, fertilizer costs, and crop values found in agriculture. Profits are higher for nutrients applied when they are more deficient in soils, under conditions of higher maximum yields and also when crop value are higher. The results point to the importance of the proper evaluation of soil fertility and to the removal of yield limiting factors. On the basis of the concepts presented on the economics of fertilizer use, the following cases were discussed: fertilizer use in extensive low value crops; policies to increase crop production with fertilizers; fertilizer use under conditions of limited capital; fertilizer recommendation for precision agriculture; choice of adequate fertilizer blends; fertilization as a sound environmental practice.

EFFECT OF CURRENT FERTILIZATION PRACTICES ON NUTRITIONAL STATUS OF DOUBLE-CROPPED TOMATO AND CUCUMBER PRODUCED WITH PLASTICULTURE

When vegetables are double-cropped on polyethylene mulch, fertilizer recommendations for each crop may need to be adjusted because liming and preplant applications are done prior to laying plastic. When current fertilizer recommendations for single crops were used for cucumber following tomato, the cucumber plants looked like green, indicating a nitrogen (N) and/or potassium (K) deficiency was developing, suggesting that nutrient availability for the second crop was not adequate for producing the highest yields. Therefore, the nutritional status of both crops was diagnosed using sufficiency range data and DRIS norms to determine which nutrient(s) was limiting crop nutrition. Regardless of N source used as a sidedress injection material (at a rate of 7 kg N ha−1wk−1 as ammonium nitrate or calcium nitrate) or liming material used to adjust soil pH to 6.5 (carbonate- or oxide-based calcitic or dolomitic lime), foliar levels of N and K, and possibly phosphorus (P) were found to be limiting factors according to sufficiency range data and DRIS norms. This study suggests that current fertility recommendations for tomato and cucumber grown as single crops in Alabama need to be reevaluated for double crops.

Development and implementation of the Virginia agronomic land use evaluation system (VALUES)

Abstract There is currently a great deal of concern about the movement of nutrients from agricultural land to surface and ground water. This concern centers on nitrogen (N) and phosphorus (P). These two nutrients greatly stimulate algal growth, ultimately causing a depletion of oxygen which adversely affects aquatic vegetation, and higher marine life. The Virginia Agronomic Land Use Evaluation System (VALUES) restructures and reorients soil test fertilizer recommendations to include the best currently available scientific technology on water quality oriented nutrient management. A data base has been developed for the major soil types in the mid‐Atlantic United States region with fertilizer rates to apply directly related to the particular soil being cultivated. This data base contains corn, soybean, and wheat yield information for over 550 soils. VALUES is being installed in the Virginia Tech Soil Testing Laboratory computer system for preparation of water quality oriented crop fertilizer recommendations.

Nitrogen Mineralization Potential of Arid and Semiarid Soils of Morocco

An accurate estimate of N mineralized from soil organic matter during the growing season is required to make correct N fertilizer recommendations for crops. In Morocco, very little information regarding the N-supplying power of soils is available. These studies were conducted to determine N-mineralization potential (No) and rate constant (k) values, N flux, and instantaneous rate of reaction for soils of the Chaouia region of Morocco. Fourteen soils were selected and net mineralizable N during 16 wk of incubation at optimum moisture and temperature was determined for each soil. Exponential and hyperbolic models were used to describe net mineralization, and No and k values for each soil were determined using nonlinear least-squares regression. Values using the exponential model ranged from 120 to 241 mg N kg−1 of soil for No and 0.06 to 0.274 week−1 for k. The values ranged from 164 to 391 mg N kg−1 of soil for No and 0.024 to 0.212 week−1 for k, using the hyperbolic model. The lowest average No values for different soils were shown to occur in Palexerolls, which are shallow soils approximately 35 cm deep that have received very low N input. Calculations using the exponential and hyperbolic models indicated the active fraction of total N in these soils varied from 7 to 22% and 10 to 36%, respectively. This study supported earlier reports that a single exponential model as well as a hyperbolic model can be used to estimate reliable No and k values in soils if a nonlinear least-squares fitting technique is used.