Dr.meter S10 Soil Moisture Sensor Meter Hygrometer-Garden,Farm,Lawn,Plants,Indoor&Outdoor(No Battery Needed), 1 Pack, Green
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- ▶ 【Helpful Tips】The Dr.meter Soil Moisture Sensor Meter is designed only for soil testing and should not be used in liquids. Keep it away from rocks and extremely hard soil to avoid damaging it. Make sure to clean the probe after each use.
Soil Analysis: Diagnosis, Quality and Assertiveness
The Beginnings of Soil Analysis
Since 50 BC in Ancient Rome the first attempts were made to analyze the soil; this diagnosis consisted of taste, acidity and salinity tests. It came to be thought that the total content of nutrients in the soils was what we wanted to know, so that later it was learned that this content did not correlate with its availability.The Evolution of soil analysis
There are three periods that define the development of soil analysis in modern times. 1) 1845 to 1906. The foundations of modern soil analysis were laid, procedures to evaluate soil fertility were evaluated and developed, there was already a first distinction between less soluble and more soluble nutrients and extractants such as carbonated water began to be evaluated, Hydrochloric acid, acetic acid and nitric acid (HNO 3) . 2) 1907 to 1924.This period was very centered between the chemical composition of the soil and the production of the crop, an abundant data base was generated that served as a foundation to improve the analytical methods and to interpret the results of the soil analyzes. It was during this period that soil fertility monitoring was promoted to avoid soil depletion . 3) 1925 to 1950. During this period two currents developed: One, in which researchers promoted the use of multi-elemental extracting solutionsand another, in which the use of extracting solutions for specific nutrients was promoted. Chapman and Kelly (1930) developed the 1M ammonium acetate extractor solution for exchange bases (Ca, Mg, Na and K), an extractor solution that is still used with excellent results today. Morgan (1941) developed the universal extraction solution that bears his name, using acetic acid and sodium acetate at pH 4.8. At the same time, Bray and Kurtz (1945) developed various procedures to evaluate available phosphorus using Ammonium fluoride + hydrochloric acid, which are still used today for the determination known as Bray P1 and P2, in the second case, with a higher HCl concentration.
Mehlich (1953) developed the multi-elemental extractant using sulfuric acid and hydrochloric acid, known as the double acid method or North Carolina method. For their part, Olsen et al . (1954) developed the extractant based on sodium bicarbonate at pH 8.5, which gained popularity for alkaline soils and is a very popular method today in America and part of Europe, for neutral and alkaline soils. Other methods were showing its ineffectiveness, such as carbonated water, which even today there are laboratories that use it, and the Mehlich method 2 which also did not show sufficient effectiveness and has been discarded in practically all laboratories.
Trends in soil analysis
The search for universal extraction solutions continues to be an issue that worries many laboratories, since together with the appearance of plasma emission spectrophotometers (ICP) it is possible to analyze hundreds of samples in a single day (Mallarino and Sawyer, 1999). This makes the analysis very economical, however recent history has told us that the quality of the diagnosis is sacrificed too much, since precision is lost when trying with a single extractant to evaluate the availability of the 12 elements: nitrates (NO 3), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), iron (Fe), zinc (Zn), manganese (Mn), copper (Cu ), boron (B) and in the case of acid soils: aluminum (Al) and hydrogen (H). Some references that support the low efficiency of multielemental methods such as Mehlich 3, are cited below: To interpret the phosphorus analysis it is necessary to know the soil analysis method before any fertilization recommendation is derived. This consideration is imperative as many methods have been developed to test the availability of phosphorus to crops. Thus, some laboratories are interested in using tests that do not use traditionally recommended extractions for P. This is where the question of whether the Mehlich 3 method is efficient or not lies. To discuss it, it is first necessary to remember that the result of a laboratory analysis is the culmination of the entire method of soil analysis, including extraction and the analytical measurement method. Mehlich 3 is a multi-element extractant and nutrients are measured in ICP. The United States Central Regional Committee for Soil Testing and Plant Analysis (NCR 13) and Iowa State University (ISU) do not recommend the determination of phosphorus with the ICP method, extracted with Mehlich 3, as variations in P concentrations measured with ICP compared to the standard colorimetric method measure up to 40% more P, and making corrections in this regard is not an effective strategy. Furthermore, they do not recommend the use of Mehlich 3 to determine Calcium (Ca), Magnesium (Mg) and Cation Exchange Capacity (CEC) in calcareous soils and micronutrients in any type of soil, due to the lack of correlation. Micronutrient interpretations, particularly zinc, are based on DTPA tests and for lime requirements in the method known as SMP, developed by Shoemaker, McLean and Pratt in 1961. For each geographic region the ISU recommends only using authorized and calibrated methods in those soils, this means the recognition of both the laboratory extraction and chemical analysis method (Mallarino and Sawyer, 1999) . For his part, Pittmanet al , 2004, testing 6400 soil samples at Oklahoma State University, found clear differences between analyzing Mehlich 3 with ICP and Mehlich 3 with the colorimetric method. Despite this, many laboratories use the Mehlich 3-ICP for phosphorus analysis, without considering that this practice could lead to the misapplication of nutrients and contribute to crop losses or negative environmental effects. Kleinman et al ., 2015, suggest that obtaining correction factors or equations is not a trivial matter, since the relationships are potentially influenced by the type of soil, and factors such as soil pH and organic matter. In Ohio soils the recommendations for phosphoric fertilization in crops are based on the Bray-Kurtz P1-colorimetric method. Comese et al ., 2007 working on rotations of corn, wheat and soybeans with increasing doses of phosphate fertilizers found that the Bray & Kurtz I method is the one that best adapts to the diagnostic practices and regional recommendations for the use of phosphate fertilizers. They concluded that Mehlich 3 overestimates the value from 15 ppm of P in the soil. Bray & Kurtz I is the method that best detected the variation of the added phosphorus doses. Performing potassium calibrations with Mehlich 3 in corn and soybeans for Iowa soils, Barbagelata et al ., 2002 detected the need to adjust K levels to interpret and make fertilization recommendations, concluding that the research should be focused on providing information to establishing different interpretations of K for different soils.
Soil analysis in Mexico
Due to the low cost of the Mehlich 3 method, foreign laboratories operating in Mexico have been encouraged to promote its use in the country. However, the country's soil specialists have not approved this procedure because it is not correlated or calibrated in Mexico and because they do not have evidence that it works correctly for the majority of Mexican soils. Its use allows to lower the cost of the analyzes but reduces the efficiency in the diagnosis with respect to the methods approved by the Official Mexican Standard (NOM-021-RECNAT-2000). Even in the United States, many more laboratories use up to 6 extractions to diagnose soil fertility than those that use the Mehlich 3 method (Sikora and Moore, 2014), for the same reasons we discuss here. On the other hand, the scientific community of Mexican soil scientists is inclined not to recommend it as a method for diagnosing soil fertility, since the lack of correlation and calibration at the regional level of a given method reduces its value for its use as a diagnostic tool. of soil fertility. This is vital to maintain credibility in soil testing with users. It is vital that Mexican laboratories adhere to the analysis methodologies established by the Official Mexican Standard.
Correlation and calibration concepts
In order for a soil analysis procedure to be authorized for its use, it must comply with the following development: 1) The evaluation of various extraction solutions and analysis methods; 2) Correlating the crop yield or the amount of the nutrient extracted by it, with the amount of nutrient extracted by each of the extractor solutions; and 3) Calibration of the analytical procedure, which consists of estimating the concentration of the extracted element at which a performance response is no longer observed, that is, estimating the critical level, above which the response to the nutrient in question is unlikely. With adequate precision, the correlation defines the analytical method that best reflects the content of the nutrient available in the soil in relation to the growth of the crop and predicts with greater precision the response of the crop to said nutrient. The degree of correlation can vary with the soil class. On the other hand, calibration is the process by which the levels considered critical are established. The most commonly used procedure to define critical levels is the one proposed by Cate and Nelson (1971), whose diagram is presented in Figure 2. Later, with other more detailed statistical regression studies, a series of interpretive values is proposed, ranging from very low or
poor, even very high or excessive. Without these values, the soil analyzes cannot be interpreted. The characteristics of these levels are presented in Figure 3, which Fertilab supports with its own research. A method that is not calibrated or correlated in the field, gives unreliable results and there are reports that even in the United States, there are many regions where the Mehlich 3 method has not been correlated or calibrated and in the best of cases only correlations with conventional methods, to estimate a conversion factor and to establish sufficiency levels for interpretation purposes.
Diagnostic methods authorized in Mexico
In October 2000, the Official Gazette of the Federation published the Official Mexican Standard 021-RECNAT-2000, which establishes the specifications for fertility, salinity and soil classification, studies, sampling and analysis with application throughout the territory. national. The purpose of this standard is that analysis service providers are duly regulated, in order to provide users with a quality service and high reliability in analytical information, preventing each laboratory from using the method that best suits them for reasons Low cost. Below is a summary of the methodologies authorized by NOM 021 for use in Mexico.
N-Nitric (N-NO 3 ). It is the N of the soil that is available for immediate use by the crop. It is extracted by means of a KCl extractor solution, followed by steam distillation. It can also be estimated using the cadmium reduction column method.
Phosphorus (P). It is determined using the Olsen Methods (neutral or calcareous soils) and Bray 1 (acidic or neutral soils). Critical levels range from 10-15 ppm for the Olsen method and 25-30 ppm for the Bray 1 method.
Potassium (K), Calcium (Ca), Magnesium (Mg) and Sodium (Na). These cations are extracted with 1N ammonium acetate at pH 7 and quantified by Atomic Absorption or by ICP. In calcareous soils it is recommended to extract with 1 N ammonium acetate at a pH of 8.5, to avoid overestimations of Calcium and Magnesium.
Iron (Fe), Manganese (Mn), Zinc (Zn) Copper (Cu). They are extracted with DTPA and quantified by Atomic Absorption or by ICP. The critical level considered for Fe and Mn is of the order of 5 ppm, for Zinc 1 ppm and for copper it ranges from 0.5 to 1 ppm.
Boron (B). It is extracted by means of a hot and diluted CaCl 2 solutionand it is quantified by ICP or Azomethine H. Its critical level is of the order of 0.8 to 1 ppm and the excessive level is greater than 4 ppm.
Sulfur (S). The method is semi-quantitative. The S is extracted with KCl and the determination is carried out in a turbidimetric way. The critical level is 5-10 ppm.
As mentioned at the beginning, the use of specific extracting solutions is the most accurate and precise way for the determination of nutrients in the soil. A laboratory adhering to the NOM and with rigorous quality control allows users to give assertive diagnoses.
Quality control in laboratories
Quality control and the use of appropriate methodologies allow laboratories to maintain certainty in the analyzes they offer. The soil analysis provided by a reliable laboratory is a robust guide to recommend fertilization rates, as it is the basis for ensuring a successful fertilization program. From this idea derives the importance of an assertive and quality diagnosis, since it will depend on it that correct decisions are made regarding plant nutrition. The establishment and monitoring of a rigorous quality control is the only way that defines "reliability" in laboratories. The purpose of the regulation is to supervise the performance of the laboratories, where Internal and External Quality Control are a very important part of the process. The intercomparison allows to measure and standardize processes with international laboratories as part of external quality control. Additionally, an internal quality control is carried out, through the use of certified standards, which allow to ensure the certainty in the analysis. These known concentration standards for each of the elements analyzed and the use of blanks are run in each batch of 10 samples and allow us to ensure the certainty of the analysis in the samples we receive from our clients. The data are statistically analyzed and allow the generation of ranges and work intervals, as well as the validation criteria of the determination. This process is called Statistical Process Control (CEP), which has also been used in the automotive industry for many years.
How to choose the services of a Laboratory?
Below are 11 criteria that serve as a guide for the correct choice of a laboratory. 1) Check how many and which determinations the laboratory makes, 2) What delivery times it offers the user, 3) Check if it is certified in ISO-9001-2008, 4) If it has international accreditations, 5) If it has intercalibrations with different laboratories in the world, 6) If it uses its own analysis methodologies for Mexico and that marks the NOM, 7) If it conducts research on its methods, 8) If it uses certified standards, 9) If it uses standard samples for every 10 analyzes, 10 ) If you have a friendly report and 11) If you give an interpretation and a recommendation of fertilization at no cost to the client. High crop yields are the result of multiple factors that begin with a good diagnosis of soil fertility. It is important to use an adequate sampling system, a good analysis procedure, authorized by the official Mexican standard, and a good analytical quality control in the laboratory. The next step is to carry out a good interpretation of the results of the analyzes and later generate an adequate recommendation for fertilization, based on a specific yield goal.
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