Template:Chapter 4.1.1

4.1.1 - Soil testing.

Dylan P. Harding, University of Guelph, Canada

Introduction

The purpose of applying fertilizer to a field is to replace the nutrients that are removed by crops. On most soils, crops will benefit from application of the macronutrients every year. Micronutrients on the other hand are generally removed by crops at a low enough rate that application is not necessary in every season. To apply fertilizers most efficiently, a farmer should ideally know the approximate level of each nutrient in the soil. Soil nutrient levels are most commonly determined through nutrient extraction tests that require specialized equipment and training to perform. Although many of these testing methods are highly accurate, they are generally impractical for poor farmers. Unfortunately, the need for more accessible methods of accurately determining soil nutrient levels has gone largely unanswered. When proactively testing soil nutrient levels is not possible, there are simple ways to characterize the soil and plan its management. Several of these low-tech methods for soil characterization are described below. It should be kept in mind that these techniques, while useful, cannot take the place of conventional soil testing, which should be taken advantage of if available. “On the spot” soil test kits are available that employ colour changing indicators to show soil fertility levels. Although these kits are inexpensive and do not require specialized training or equipment to use, the accuracy of these kits varies widely. In a comparison of the results of 5 different home soil test kits sold in the US to laboratory analysis of the same soil, agreement between the home soil test kit results and laboratory results ranged from 33% to 94% (Faber, Downer, Holstege, & Mochizuki, 2007). The accuracy of nutrient indication also varied between minerals with the accuracy of potassium levels being most consistent and the accuracy of phosphorus levels being the least consistent (Faber et al., 2007). Only pH and macronutrient levels were indicated by the kits tested. It should be noted also that most home test kits indicate soil nutrient levels to be simply “low”, “medium”, or “high”, rather than providing specific values from which the most efficient fertilizer rate could be calculated. For further information on important characteristics to look for in an accurate soil test kit, please see the work of Faber et al., (2007) entitled “Accuracy Varies for Commercially Available Soil Test Kits Analyzing Nitrate–Nitrogen, Phosphorus, Potassium, and pH”. It is important to keep in mind that home soil test kits are not as accurate as laboratory analyses, and should only be employed where more accurate laboratory testing is not available.

To determine if laboratory soil testing is available in a given area, the best course of action is generally to contact the regional or national ministry of agriculture, or local agricultural universities where they are present. These institutions often have internal soil testing labs or may be able to provide contact information to local soil testing labs.

To determine if laboratory soil testing is available in a given area, the best course of action is generally to contact the regional or national ministry of agriculture, or local agricultural universities where they are present. These institutions often have internal soil testing labs or may be able to provide contact information to local soil testing labs.

Benefits

There are a number of benefits associated with adding organic nutrients to home gardens and smaller plots of farmland. Organic ingredients added to soil help improve soil health and structure, particularly sandy soils, increasing their workability and allowing the soil to hold moisture better (Pleasant, 2012; Román, 2015). Organic addition also helps to regulate soil moisture, reduce water loss through evaporation, and lower the risk of erosion (Román, 2015). These qualities are invaluable to the long-term sustainability of soil. Not only do the organic nutrients benefit the physical properties of the soil, but they add chemical nutrients that assist with increasing yields, such as nitrogen, potassium, and phosphorous (amongst others) (Román, 2015; Lynch, 2014). Another advantage of organic fertilizer is that it reduces pollution of the soil, water, and air, when compared to synthetic fertilizers (Schwarz and Bonhotal, 2011). Finally, an advantage of organic nutrients is that they work to increase yields without costing farmers money. Organic fertilizers can be made using household waste, human waste, and cooking waste. Though synthetic fertilizers can be advantageous to farmers, they are often unavailable in very remote regions of developing countries. Additionally, they can be expensive and farmers may be unclear about how to apply them. When farmers know how to add inexpensive and easily accessible organic nutrients to their gardens and fields themselves, they become more self-reliant.

Table 1: The following table provides some examples of compost inputs and their macronutrient contents

Instructions

This section will outline two different methods of adding organic nutrients to gardens and fields previously mentioned: compost, and urine. Composting: Composting is more intensive than using urine, but high quality compost can be created through a variety of inputs and combinations; it is about balancing the green and brown inputs. This means that farmers in Bolivia, Sudan and Laos alike can use whatever compost ingredients they may have at their disposal and can be successful. Green feedstocks (compost ingredients) are nitrogen-wet materials, including food scraps, manure, and green trimmings. (Schwarz and Bonhotal, 2011). By contrast, brown feedstocks are carbon-dry materials, such as straw, woodchips, brown leaves, and soiled paper (Schwarz and Bonhotal, 2011). First, kitchen scraps must be collected from the household (although meat and dairy products should be excluded as they are not ideal for home composting) (Schwarz and Bonhotal, 2011). It would be helpful to have a location outside or a container to place the kitchen scraps. The second step is to collect scraps such as leaves, brush, and weeds. Third, a place must be chosen to mix the compost and allow it to decompose. This space must be large enough for a large quantity of compost, since the pile must retain its own heat in order to decompose faster (minimum size of one cubic yard). The temperature also should be considered when selecting a spot; in cool climates the compost should sit in the sun to allow it to receive the maximum amount of heat possible, while in warmer climates it should be in the shade so as not to dry out (Schwarz and Bonhotal, 2011). The next step is to mix the compost, which is done by layering the browns and greens, starting with a layer of brown feedstocks and followed by greens in a well on top. Another layer of browns should be added, followed by greens, and so on. These steps of layering should be continued until all the ingredients have been used, all while keeping the greens towards the middle, so that only the browns are visible (Schwarz and Bonhotal, 2011). Turning the pile with a pitchfork or shovel, as well as adding water can help to speed up the decomposition process (Schwarz and Bonhotal, 2011). The compost takes about six months to a year to transform, and then can be added to the soil to enable crop production (Schwarz and Bonhotal, 2011).

To determine if laboratory soil testing is available in a given area, the best course of action is generally to contact the regional or national ministry of agriculture, or local agricultural universities where they are present. These institutions often have internal soil testing labs or may be able to provide contact information to local soil testing labs.

The timing of soil testing can be very important. Some forms of mineral nitrogen (e.g. nitrate) is extremely mobile in the soil and for this reason soil testing (if possible) should be done within a few days of fertilizer application to ensure the test results are still accurate. Mineralization of organic nitrogen and loss of nitrogen to the environment will quickly cause variation from the test levels. Mineral nitrogen can easily be lost within a few days if there is no vegetation to absorb it (Principals of Plant Nutrition, 2001). Nitrogen loss is promoted following heavy rainfall causing leaching, and through conversion to gas when oxygen is unavailable (e.g. when a clay soil is waterlogged) (Principals of Plant Nutrition, 2001).

Areas such as Africa and South Asia that have not (on a geological time scale) been recently glaciated tend to have soils with lower nutrient holding capacities and overall lower nutrient contents (Lotter, 2010). Although there is variation between areas, this general trend will pervade in most soils within these regions. Global maps of soil characteristics such as depth, pH, dominant soil type, etc. are available from the FAO at http://www.fao.org/nr/land/soils/en/. It should be noted that these maps indicate the general trends in soil types within an area, but one should expect variation within these trends when individual fields are investigated.

The underlying bedrock material will have a strong influence on a soil’s mineral content, particularly for potassium, phosphorus, and calcium and this should be considered when planning the management of a soil. Local departments of geology, where established, will often be able to provide information on local bedrock composition.

Soil Nutrient Diagnosis Using Plants

The most effective method of determining whether or not a given fertilizer will have a beneficial effect on crop growth is through doing a small split-plot trial. To do this, a small test plot should be established in which half receives a consistent application of the test-fertilizer, and the other half does not. The management of the entire plot should otherwise be as consistent as possible, and ideally the farmer should not know which half of the plot is which to encourage consistent management. If the application of fertilizer is found to cost-effectively improve crop yields, then wider use of the fertilizer can be considered

Alternatively, the easiest way to recognize nutrient deficiencies in crops without specialized equipment is through observing symptoms of deficiency as they develop in crops. However, this is not the most ideal method of recognizing nutrient deficiency as by the time a shortage becomes observable in a crop it may be too late for fertilizer application to improve growth in that season. Also, many plant nutrient deficiencies have similar symptoms and thus can be confused with one another. However, where soil testing is not practical this method may be the most effective way to learn which nutrients are most needed in a given field. Links to image galleries of nutrient deficiencies as they appear in common crops are provided at the end of this chapter.

Table 1, below, provides descriptions of nutrient deficiencies as they appear in crops. The relative speed with which a given nutrient is transported through the plant affects where the deficiency will be exhibited. In general, deficiency of nutrients the move through plants relatively slowly will appear in new leaves and shoots, and deficiency of highly plant-mobile nutrients will appear in older leaves and the lower stem. Recognizing the relative mobility of the deficient nutrient can help narrow down the possible range of nutrients that are limiting crop growth.

Programs for cell-phones and other mobile devices that provide photo galleries of crop nutrient deficiency symptoms are also useful tools. The International Plant Nutrition Institute (IPNI) offers a Crop Nutrient Deficiency Photo Library that can be downloaded for about $5 (see below). Programs such as this are convenient because they enable on the spot comparison of field conditions to reference photos. The application “Learning Plant Language” from Agronomic Acumen serves a similar purpose, and is available for about $30. The International Potash Institute offers a free App that provides a photo gallery of potassium deficiency symptoms for various crops. The “Nutrient Removal Application” from Ag-PhD is another useful tool that provides estimates of nutrient removal rates of different crops based on yield. Links to these tools are provided below.

Soil nutrient concentrations can significantly vary over a small area, and for this reason symptoms of nutrient deficiency may appear in patches throughout a stand of crops. If patchy symptoms are observed in a field, subsequent soil testing should be performed to compare nutrient levels between areas where deficiency is exhibited and areas where it is not, if possible. When patches of deficiency symptoms are observed, these areas should be prioritized for subsequent application of the apparently deficient nutrient. Applying fertilizer only to areas that exhibit crop deficiency symptoms can also be considered if additional methods of soil testing are not available, or if the nutrient considered to be deficient is in short supply.

It should also be kept in mind that non-nutrient related challenges to the growth of a crop can create the impression of a mineral deficiency. For example, pests such as nematodes can damage a crop’s root system, limiting its nutrient uptake capacity and thus creating the appearance of a mineral deficiency despite potentially sufficient levels of that nutrient in the soil. Many crop diseases can also cause symptoms that are similar in appearance to nutrient deficiencies. For this reason, field testing with a reliable soil test kit or ideally through the establishment of a trial plot (described above) are important tests to perform when nutrient deficiency is suspected.

There is likely potential to understand soil nutrient balances through observing which wild species tend to do well on a given field. The available literature suggests that indicator species are generally used to estimate overall soil fertility, a measure which is obscured by the influence of many different factors. Unfortunately, there is little available information that associates indicator species with deficiencies or abundances of specific nutrients. Indicator species could perhaps be used as indicators of less variable soil characteristics such as cation exchange capacity, pH, and structure, which are each explained in greater detail below. Further investigation, ideally combining indigenous knowledge with modern nutrient testing, may help illuminate the use of wild plant populations to estimate soil nutrient levels.

Cost Analysis

These solutions are very low cost, with the only tools required being a shovel or pitchfork for turning compost and a jerry can for urine storage. However, if farmers do not own sufficient livestock then manure must be purchased, which can be expensive.

Further Reading

Here are some reports for further understanding on each of these organic fertilizing practices: Composting:

http://cwmi.css.cornell.edu/compostingathome.pdf

http://www.fao.org/3/a-i3388e.pdf

http://www.fao.org/docrep/014/i2230e/i2230e14.pdf

Urine:

http://www.ecosanres.org/pdf_files/ESR2010-1-PracticalGuidanceOnTheUseOfUrineInCropProduction.pdf

References

1.Adeniyan, O.N. et al. “Comparative study of different organic manures and NPK fertilizer for improvement of soil chemical properties and dry matter yield of maize in two different soils.” Journal of Soil Science and Environmental Management 2.1 (2011) : 9-13. Web.

2.AdeOluwa, O.O. and O. Cofie. “Urine as an alternative fertilizer in agriculture: Effects in amaranths (Amaranthus caudatus) production.” Renewable Agriculture and Food Systems, 27.4 (2012) : 287-294. Web.(2016).

3.Edwards, Sue and Hailu Araya. “How to Make and Use Compost.” Climate Change and Food Systems Resilience in Sub-Saharan Africa Food and Agriculture Organization of the United Nations (2011) : 380-436. Web.

4.Edwards, Sue et al. “Impact of Compost Use on Crop Yields in Tigray, Ethiopia.” Natural Resources Management and Environment Department, Food and Agriculture Organization of the United Nations (2007) : 1-55. Web.

5.Giri, Anjana and Klaus Katzensteiner. “Carbon and Nitrogen Flow in the Traditional Land Use System of the Himalaya Region, Nepal.” Mountain Research Development 33.4 (2013) : 381-390. Web.

6.Halberg, N. et al. “Global Development in Organic Agriculture: Challenges and Prospects.” Danish Research Centre for Organic Food and Farming. CABI Publishing (2006) : 1-392. Web.

7.He, Zheni et al. “Plant Nutrition Benefits of Phosphorus, Potassium, Calcium, Magnesium, and Micronutrients from Compost Utilization.” Compost Utilization in Horticultural Cropping Systems (2001) : 307-320. Web.

8.Izugbara, C. Otutubikey and J.O. Umoh. “Indigenous Waste Management Practices Among the Ngwa of Southeastern Nigeria: Some Lessons and Policy Implications.” The Environmentalist 24 (2004) : 87-92. Web.

9.Lynch, Derek H. “Sustaining Soil Organic Carbon, Soil Quality, and Soil Health in Organic Field Crop Management Systems.” Managing Energy, Nutrients and Pests in Organic Field Crops, Edited by Ralph C. Martin and Rod MacRae, CRC Press (2014) : 107-131. Web.

10.MacRae, Rod et al. “Introduction.” Managing Energy, Nutrients and Pests in Organic Field Crops, Edited by Ralph C. Martin and Rod MacRae, CRC Press (2014) : 1-6. Web.

11.Misra, R.V. and R.N. Roy. “On-Farm Composting Methods.” Food and Agriculture Organization of the United Nations (N.D.) : 1-26. Web.

12.Paungfoo-Lonhienne, Chanyarat et al. “Past, present and future of organic nutrients.” Plant Soil 359 (2012) : 1-18. Web.Web.

13.Pleasant, Barbara. “How to Make Compost.” Mother Earth News 254 (2012) : 52-58. Web.

14.Richert, Anna et al. “Practical Guidance on the Use of Urine in Crop Production.” EcoSansRes Series. Stockholm Environmental Institute (2010) : 1-69. Web.

15.Román, Pilar, María M. Martínez and Alberto Pantoja. “Farmer’s Compost Handbook: Experiences in Latin America.” Regional Office for Latin America and the Caribbean. Food and Agriculture Organization of the United Nations (2015) : 1-112. Web.

16.Roy, R.N. et al. “Plant nutrition for food security: A guide for integrated management.” FAO Fertilizer and Plant Nutrition Bulletin. Food and Agriculture Organization of the United Nations (2006) : 1-348. Web.

17.Schwarz, Mary and Jean Bonhotal. “Composting at Home – The Green and Brown Alternative”. Cornell Waste Management Institute. Department of Crop and Soil Sciences, Cornell Cooperative Extension (2011) : 1-12. Web.