Do Soybeans Cause Soil Depletion?

Nutrients

Like all plants that are intensively grown as cash crops, soybeans remove nutrients from the soil to grow. Millions of tons of soybeans are harvested each year and these nutrients are lost from the soil. However, soybeans are fertilized each year, so these nutrients are replaced. In addition to the fertilizer needs of soybeans, they also naturally add an essential plant nutrient to the soil. Because soybeans are a legume plant, they allow nitrogen-fixing bacteria to live in their roots. These bacteria form a symbiotic relationship with the soybean plant and take nitrogen from the atmosphere and turn it into a form that is usable to plants. Without nitrogen, plants cannot grow. Thus, unlike corn, soybeans actually increase the vital plant nutrients in the soil.

Plants like soybeans that are grown in intensive agricultural settings cause damage to the soil by worsening soil structure. This damage is primarily brought about by the use of heavy machinery such as tractors and combines. Poor soil structure lacks aggregates of soil particles. Without small clods, the soil is free to be blown or washed away. Soil structure provides an anchor for plant roots. If the soil for soybeans is tilled and plowed often as most farmers do, it will begin to become susceptible to erosion. After many years of intensive farming, a soil used to grow soybeans can become physically depleted by being carried off by erosion.

Growing soybeans clears the soil of the natural diversity of plant life on the soil surface. By getting rid of all of the perennial plants that might have grown on that soil and replacing them with an annual crop, the soil is stripped of the permanent roots that used to hold it in place. When the soil is bare, not only is it more likely to erode, but nutrients can also leach out of it faster. Since there are no roots to hold the soil together and fewer plants throughout the year, nutrients can become more depleted than they normally would under natural conditions.

Soybeans are one of the crops most used in no-till farming. No-till farming reduces the amount of tractor traffic on a field significantly and leaves the stubble from the previous year's crop in place. These management techniques significantly reduce the amount of damage done to the soil structure. No-till farming also makes the soil much less erodible since it is not being worked as often and roots are left in the ground to anchor the soil. By using no-till when farming soybeans the soil is significantly enriched due to the slower pace of physical soil depletion and the increased nitrogen in the soil from growing soybeans.