By Jennie Schmidt, MS, RD, Owner and Operator of Schmidt Farms, Inc.

Soil is the lifeblood of a family farm and our food supply. It is a dynamic and complex system composed of minerals, air, water, and organic matter. The health of soil is defined or determined by the attributes that impact plant health and productivity. Plants need 17 elements to grow and produce: carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, calcium, magnesium, potassium, chlorine, iron, manganese, zinc, copper, boron, nickel and molybdenum. The source of 14 these elements (all except carbon, hydrogen, and oxygen) is soil. The degree to which these are found is largely dependent on the parent material of the soil and influenced by climate, environment, and human interventions.

Soil quality can be defined as a soils capacity to function, with ecosystem or landuse boundaries, to sustain plant growth, maintain air and water quality, and support human and animal health. Agronomically speaking, quality soil has good “tilth” meaning it drains well, resists compaction, erosion and nutrient loss, and supports soil organisms and productive yields.

Farming practices influence the quality of agricultural soils. Tillage is one example that can help or hinder soil. “Conventional” tillage such as plowing is the most severe form of tillage. Plowing turns the soil over deeply, which controls weeds but significantly exposes the soil to wind, rain and erosion. “Conservation tillage and “No-Till” farming leaves some or all of the previous crop’s residue on the soil surface and plants the next crop directly into the soil. Family farms have become increasingly conservation minded as 63 percent of all US farmland is conservation tilled of which nearly 36 percent is no-till.

Crop rotation is another soil building practice of rotating the crops that are planted each season. Crops are rotated by botanical family to alleviate pest and disease pressure and replace nutrients taken up by the previous crop. Vegetable crops within the same botanical family follow a 4 year crop rotation so as not to perpetuate the same diseases and pests those plants are susceptible to.

Cover crops are planted between harvests and serve several purposes. Cover crops act as nutrient “sponges” taking up and conserving nitrogen and other nutrients left over from the previous crop. They also build organic matter, improve drainage, keep nutrients from moving to waterways, and reduce erosion and runoff.  Forage or Daikon radish has become a popular cover crop. The radish has a very long tap root which breaks up compaction, oxygenates the soil and facilitates water filtration. They also soak up significant amounts of nitrogen, phosphorus, sulfur, calcium and boron.  The radishes winter kill in cold temperatures and as they decompose, release those nutrients back to the soil.

Soil is the “diet” for the crop, providing the main source of nutrients utilized by the plant. This is referred to as nutrient uptake because as a plant grows, it takes up nutrients from the soil to both its vegetative and reproductive portions, including the roots.  Nitrogen, phosphorus, and potassium are the “primary macronutrients” used by plants. Nitrogen is a functional part of chlorophyll and is essential in the formation of amino acids and proteins. Phosphorus is essential in energy transfer, photosynthesis, respiration, and cell division.  Potassium is required for the synthesis of both carbohydrates and proteins.  Other elements such as calcium, sulfur, magnesium, boron, and other essential nutrients function to assist in the vegetative and reproductive phases of plant growth and ultimately harvest.

Soil testing is conducted to determine the level of nutrients present. Farmers base their nutrient management decisions soil test results and crop needs to achieve the yield goal. When a soil is deficient in a certain nutrient, or does not have the sufficiency to meet the crop needs, amendments can be applied either to the soil as fertilizer or as a “foliar feeding” applied to the plant tissue itself. One example is boron, which is highly leachable in some soil types. Boron is critical in fruit set, the establishment of the fruit-bearing part of the crop, such as cucumbers, grapes, strawberries, tomatoes and even corn and wheat.  Boron applied to the soil or to the plant tissue prior to the critical reproductive phase called “bloom” will improve fruit set. The level of boron available to the plant affects its reproductive abilities and ultimately the quality of the crop to be harvested.

Nutrient content that is present in the harvestable crop is used to determine “nutrient removal.”  As plants photosynthesize,   the demand for each nutrient varies depending on the stage of growth.  Plants that remove significant nutrients at harvest have good levels of that nutrient as a food, such as potatoes and potassium. Potassium which functions to synthesize carbohydrates and proteins, is deposited in the tuber of the potato plant during the reproductive phase of tuber growth. Insufficient potassium will result in smaller potatoes with lower starch content but not necessarily lower potassium.

There is not a direct correlation between the level of nutrients present in the soil and the amount present in the plant.  It is possible to have sufficient soil nutrients available and still show deficiencies in the plant. Incorrect soil pH limits the plant’s ability to take up nutrients.  Drought restricts the ability of the plant to take up nutrients from the soil as does a damaged root system from pests like nematodes.

Some research has shown that nutrients in fruits and vegetables have declined over time, in part due to “genetic dilution” of breeding cultivars for higher yields. Other research has shown that there are significant variances in mineral and flavonoid composition of fruit and vegetables each growing season, indicating that cultivar selection, growing conditions, and cultural practices are strong contributors.

Farming practices related to soil have a strong but not exclusive relationship to the nutrients present in food. Farm families strive to not only produce healthy foods but to maintain healthy soils in order to keep the farm sustainable for future generations.
 
Jennie Schmidt, MS, RD is a member of a 3rd generation family farm who practice synergistic farming – using practices from all farming systems and implement these Best Management Practices (BMP) discussed in this article on their soils to leave a sustainable farm for future generations.