Every crop uses a different amount of nutrients: nitrogen, potassium, phosphorus, sulphur. As crops are combined and sent to the cities around the world to feed people, these nutrients are no longer available. The circle of life where all nutrients taken from the land are eventually put back onto the land is broken as consumers live away from modern agriculture.
Each fall/spring we soil test our grain fields. By knowing the nutrient profile of the soil we can plan what crop we want to plant on that field the next spring and what fertilizer it might need to grow a healthy crop. Nutrient deficiencies within the soil are referred to as “mining the soil”. This occurs when soils are steadily depleted of nutrients and not replaced with either organic (manure) or chemical fertilizer.
What is soil testing
Soil is a mixture of minerals, organic matter, and countless organisms that together support life on earth. A soil test is the chemical analysis of a soil sample to determine nutrient content, composition, and other characteristics such as the acidity or pH level.
Why soil test
A soil test determines soil fertility levels that assist in making good nutrient management decisions. Appropriate nutrient application can increase yields, reduce production costs, and prevent surface and groundwater pollution.
Soil testing provides a guideline, it is not an infallible guide as other factors also come into play, but soil tests do help to inform fertilizer applications for a field depending on the crop that will be planted to avoid ‘mining the soil’ and to avoid over-application that can result in water contamination. This also helps with planning fertilizer purchases in the fall, when prices tend to be more favourable than in the spring.
What to soil test
Soil nutrient levels vary from year to year, and frequently will vary within fields, even in fields that seem very uniform. But an understanding of general nutrient status can be gained from regular soil testing.
Nitrogen testing is recommended annually as the available nitrogen can change considerably from year to year. Changes are dependent upon environmental conditions such as rainfall and temperature patterns during a growing season, type and yield of crop harvested, date of harvest, fall tillage, and amount of fertilizer applied to the previous crop.
While potassium and phosphorus levels do not change substantially. The common soil analysis packages usually include all 4 main nutrients (nitrogen, potassium, phosphorus and sulphur).
How to soil test
To get accurate soil tests we must collect representative samples from the field. Uniform fields can be sampled in a simple random pattern across the field. We want to collect at least 15-20 cores of equal size. Fields with more variation across landscape are divided into separate sample areas.
Poor soil sampling technique can cause variation in fertilizer recommendations. Soil testing is only as good as the quality of the samples collected. Therefore, good soil collection procedures is critical. We follow these soil test procedure general sampling guidelines.
Soil can be managed to improve organic matter by planning to leave crop residue in the field (by spreading the straw and chaff evenly behind the combine). Fields that have high yield and need additional nutrients may receive manure from the backgrounding lot when it is spread. Overall there are a number of management practices a farmer will use to ensure soil fertility that is sustainable for annual cropping (this may include perennial forages in the rotation) while ensuring those nutrients stay on the land (where they are meant to do a job) and not leech through the soil contaminating waterways.