Soil And Plant Analysis - Use A Lab Or Do It Yourself

Dairy farmers in the region submit plant and soil samples for analysis to feed and fertilizer companies and to private laboratories. Analytical procedures vary among laboratories so results are not always comparable. Some laboratories base fertility recommendations on outdated models that do not adequately credit the nutrients in manure or other organic soil amendments. Make sure that the laboratory you are using is current and uses local research to develop its recommendations.

Farmers now have the option of using on-farm quick-tests to do some analyses. On farm kits have several advantages:

Testing is inexpensive. Once the test kit is paid for, each analysis costs much less than a laboratory. Also, the inconvenience and cost of shipping samples is avoided.

Quick results. Results are available within minutes or hours of collecting the sample, depending on the test kit. Commercial laboratories typically have at least 2 - 3 day turnarounds, plus shipping time. Conditions during transportation may affect results.

Accuracy. Some of the test kits now available for soil, plant and manure analysis can produce very accurate results.

Note that because grassland systems are fertilized and manured frequently, an inexpensive reliable quick-test is especially handy for fine-tuning rate of application.

Quick-tests also have some drawbacks:

Consistent results. To get accurate results, the operator must use precise and consistent techniques. When testing samples only 3 or 4 times a year, it can be difficult to maintain identical technique each time.

Complicated procedures. Some test kits require that the user have considerable skill to meticulously follow instructions. While some quick-test kits have proven results under controlled conditions, they may be less effective in on-farm situations. Interpreting the results. Knowing soil nutrient content is of no use unless the results can be used to guide rates of nutrient application. Test kits should be furnished with an interpretation based on local research.

Verification necessary. It is generally recommended that duplicate samples should be periodically sent to a commercial laboratory to verify the performance of the kit.

Fig 22. Nova MKII meter measures ammonium-nitrogen concentration in manure.

Manure Quick-Test Kits

1. The Nova MKII nitrogen meter from Sweden provides a value for the ammonium-N concentration in manure. This test takes less than 10 minutes to complete and is generally accurate to within 10% of laboratory values. (Available from Grass Roots Project Management, PO Box 136, Chilliwack, BC, V2P 6H7)

A measured volume of manure is mixed with a chemical reagent in a sealed container. The reaction releases nitrogen gas, creating pressure in the chamber. A pressure gauge is calibrated to give the ammonium-N concentration in the manure. Where manure application rates are based on ammonium-N, this test kit is adequate.

2.The hydrometer is a cheap and simple tool used to estimate total solids content of manure. (Available from Whatcom Conservation District, 6975 Hannegan Rd., Lynden, WA, 98264)

The hydrometer consists of a glass cylinder with a weighted bottom. It is placed in a bucket of well-mixed manure and allowed to float for 15 sec. Very thick slurry may need to first be diluted. The solids content can be read directly. Calibration charts are used to correlate the solids with nitrogen and phosphorus content. Considering the benefits of diluting thick slurries on crop response (see Fig 7 and 8), the hydrometer is useful for determining how much water to add to reach a desired solids content.

Soil Quick-Test Kits

1. 'NITRACHEK' Reflectometer. This field kit rapidly tests both available ammonium and nitrate content in soil in about one hour. The procedure involves reading paper test strips with a reflectometer. Nutrients are extracted from undried soil with a potassium chloride solution. Adjustments for soil water content are made by means of a standard dilution procedure. This test gives very accurate results, typically within 5% of laboratory values.

2. Nitrate Quick Test. This kit tests only for nitrate-nitrogen and requires that soil samples first be dried at room temperature. Nitrate Quick Test has been found reliable and accurate for Fraser Valley soils with the following qualifiers:

-Nitrate should be extracted with aluminum sulphate rather than potassium chloride. -For soils with low nitrate concentration, a lower dilution should be used (i.e. 2:1 rather than 10:1)

(Hawk Creek Laboratory, Inc. Box 386, Glen Rock PA, 17327)

3. Cardy Meter. This procedure tests for nitrate in soil after air-drying. The dry soil is mixed with an extracting solution and filtered. A few drops of filtered extract are placed on the hand-held nitrate ion meter. Nitrate readings are in parts per million. The bulk density of the soil must be known or estimated to convert to kg/ha (or lb/ac) of nitrate-nitrogen. While not quite as accurate as the Nitrate Quick-Test, the Cardy meter is very simple to use. (Spectrum Technologies, Inc.)

4. N-Trak. The N-Trak test kit is promoted by Iowa State University and used widely in the Midwestern U.S. Soil extract is treated with cadmium and produces a colour reaction depending on nitrate concentration. Nitrate concentration is determined by matching the treated extract with colour chips. This test kit requires subjective colour assessment. Safe disposal of the cadmium reagent must be attended to. The N-Trak is also fairly easy to use.

Crop Indicators

Silage or hay samples are often analyzed for nutritional quality to develop balanced rations for livestock. The crude protein and nitrate information can also be used to assess fertility practices. High protein levels (over 18%) result from short cutting intervals but also suggest very high rates of nitrogen application. High nitrate levels (over 0.1% nitrate-nitrogen) in tissue indicate a possible health hazard for livestock but also suggest excessive application of nitrogen from manure or fertilizer. In general, crude protein levels of 16-18% with nitrate-nitrogen below 0.05% suggest sound nitrogen management, although factors such as variety of grass, stage of growth, weather conditions and time of year need to be taken into account.

A new hand-held instrument called 'SPAD meter' (Minolta Ltd.) is being used in the field to detect nitrogen deficiency in several crops including corn and tobacco. The instrument clips onto a leaf and gives an instant measurement of leaf colour. It detects slight differences in leaf greenness, which is greatly influenced by nitrogen status, although other factors (variety, sulphur, drought, etc) are also involved. This instrument holds promise for use on grass.

Finally, crop response to applied nutrients can be directly evaluated with test strips in the field. Applying more or less fertilizer to strips in a field for comparison is an excellent way to assess the benefit or need for fertilizer. It may be possible to use 'pasture probes' to detect differences in production among the test strips that would go unnoticed visually.

The Value of Manure Analysis and Record-Keeping

Because there is no reliable soil nitrogen test for forage production in this region, producers are encouraged to use the best alternative approach to nitrogen management: establishing a proper record-keeping system. Over time, the records tell a story - they become a report card that shows how well nitrogen and other nutrients are being managed on the farm. Year-to-year variation in weather conditions causes short-term fluctuations in values for the various records, but after three or more years of record keeping, farm trends will emerge. Proper records of nutrient management should contain the following information:

- Soil test results
- Fertilizer applications - time, rate and analysis
- Manure applications - time, rate and manure analysis
- Forage yields (preferably on a dry matter basis)
- Forage analysis (crude protein, potassium, ADF, NDF, moisture)
Large differences in farming operations mean a wide range of nutrient concentrations in manure. Seasonal variation in manure nutrients occurs within farms, particularly those using uncovered storage. Consequently, manure analysis is always recommended. In the first year or two, have the manure analyzed 3-5 times during the growing season. If overall management remains constant and manure analysis results remain consistent from year to year, the frequency of analysis can be reduced.

A computerized system for keeping nutrient records was developed by D. Grusenmeyer and T.N. Cramer of Washington State University Cooperative Extension, Bellingham, WA. Computer diskettes are available from WSU without cost.