Yuma Ag and You: Soil Quality and Management

Bobbi Stevenson-McDermott         February 19, 2017 publication

Wheat is an amazing crop! It seems to sprout as soon as the water touches it and to grow by leaps and bounds. Growers are now planting their rotation crops, wheat, cotton and Sudan grass. In addition, watermelon, honeydew and cantaloupe transplants are going in the ground. More and more crops are being transplanted than in years past. The technology of growing transplants has greatly advanced as well as the equipment to efficiently plant the seedlings. The benefit of using transplants is that the grower knows he has a live plant. Precision planting reduces the need for thinning, and more effective use of agricultural chemicals is possible since the plants are already there during field treatments.

In talking with growers, soil quality and management is becoming a greater topic. Yuma County soils contain less than one-half percent organic matter which is leaves, stalks and other plant materials that are returned to the soil after a crop is harvested. Many growers also utilize composted manures to add organic matter to the soil. Composted manures are heated to a temperature which kills weed seeds and harmful micro-organisms, meeting food safety requirements. With our irrigation, tillage and high temperatures, organic materials break down very rapidly. Another technique for adding organic matter is to grow green manure crops. Most commonly legumes, these crops can capture nitrogen from the air and fix it in the plants, making them high in protein. Because most crop residues contain much more carbon than nitrogen, and bacteria in the soil need both, the nitrogen supplied by legumes speeds the decomposition of crop residues in the soil into organic matter.

Some of the legumes have aggressive taproots, reaching 6 to 8 feet deep and a half inch in diameter that open pathways deep into the soil. The root channels increase porosity, promoting air movement and water percolation deep into the soil. Research in both the United States and Canada indicate improved soil physical properties following legumes. These improvements in soil structure are attributed to increases in organic matter and microbial activity that bind the soil particles together. The protein Glomalin, released by fungi that live along the roots of legumes and other plants, serves as the glue that binds soil together into stable aggregates. Aggregate stability increases pore space and ease of farming while reducing soil crusting.

Soil compaction is a real problem in vegetable production and is increased by being in fields when the soil is wet. Crops have to be harvested regardless of the weather. Foot traffic, harvest aids, haul trailers and tractors and larger equipment used when others bog down in the mud, are all realities growers deal with. With the importance of the produce industry to the local economy, it is important to heal as much of the damage in preparation for the next season. For any soil building rotation to be effective, it must be given time to work. As soil diseases, low fertility and poor soil structure increases, the quality and quantity of the plants being grown will decrease. There has been discussion of buyers including crop rotations and soil improvement rotations in their contracts with growers to increase soil quality and future crop health. Competition for the available farm leases may create opportunities to include the improved soil practices as a lessee cost and reduce rents. The soil is as important to the success of our agricultural industry as the water and climate.