Land and Soil – United States
Reducing erosion – improving productivity
Due to technological advances in production and best management practices in the U.S, cotton yields have doubled even as less land is planted. To be exact, there has been a 31% reduction in land required to produce one kilogram of cotton lint since 1980 (Field to Market, 2016).
A huge factor in this improvement is soil conservation. Soil is agriculture’s most fundamental resource and a study in nature’s patience. It’s continually being produced from parent material – and continually being lost to wind and rain. Modern production practices allow cotton growers to achieve high levels of soil conservation while increasing soil health. The outcome: increased yield, reduced production costs and a better long-term outlook for the farm’s productivity. Soil improvements have even resulted in cotton plants experiencing less drought stress during short-term rain-free periods.
The environmental and economic benefits, coupled with mandatory regulations and requirements for compliance, are strong incentives for producers to take every practical measure possible to protect the soil. However, there’s a negative motivation as well: as intense rain events become more frequent due to climate change, grower interest in cover crops and other erosion control practices will only increase.
"Producing 1 kilogram of cotton lint requires 31% less land now than it did in 1980."
– Field to Market, 2016
For cotton growers, maintaining soil resources has a big impact on how productive their land will be and how economical their crops will be. But, beyond just being a fiscally sound idea, preserving soil quality is actually part of the United States’ federal environmental standards for soil management. Specifically, crop producers must submit a Conservation Compliance Plan to the U.S. Government for approval. The 1985 Food Security Act introduced the Conservation Compliance and Sodbuster programs to minimize soil erosion. In 1995, 90 million acres of cropped Highly Erodible Lands (HEL) in the U.S. were subject to conservation plans and those requirements are still in effect today (Stubbs, 2012). Approved plans are mandatory for any grower wishing to participate in the crop program, and enforcement is strict.
Growers can turn to the National Resource Conservation Service (NRCS) for assistance in implementing soil conservation practices on their farms. A part of the U.S. Department of Agriculture, the NRCS develops conservation farming techniques and practices that help preserve the nation’s soil resources. Soil health is a major priority for the NRCS. One NRCS initiative is designed to expand the benefits of rhizosphere biology (nutrient and water uptake through the roots) by increasing the soil organic matter and diversity of shoots, roots and microbes grown in the field.
Soil conservation practices
U.S. cotton growers are making great strides in reducing soil erosion and encouraging high-quality soil creation through a variety of farming techniques. Since the late 1990s, cotton has made great strides in reducing the use of tilling and in adopting the practice of growing winter or cover crops. Research shows that these improved conservation tillage practices dramatically reduce soil erosion, and actually bring these activities into balance with soil creation (Montgomery, 2007). (See the next section to learn more about conservation tillage.)
The implementation of erosion-control methods is not only vital in maintaining agricultural viability, but also is in the best interests of cotton growers for financially sound economic development and sustainability for the generations ahead. The cost to replace soil functions and remedy off-site damage due to soil erosion has been estimated at a minimum of $3 to $10 per ton of soil; the cost of productivity losses is even greater (Hansen and Ribaudo, 2008).
Modern agriculture now uses many management practices to preserve soil, such as:
- Wind breaks – Planting trees in lines along crop fields to reduce wind erosion
- Contour farming – Orienting crop rows perpendicular to the natural slope of the land to reduce water erosion
- Conservation tillage – Preserving crop residue on the surface of the fields and reducing the number of tillage operations, meaning decreasing the number of times fields are cultivated to control weeds or plowed to disturb the soil
Conservation tillage practices have been widely adopted across the U.S. More than two-thirds of U.S. cotton growers employ some form of conservation tillage (Reed et al., 2009), and between 2008 and 2015, the number of growers using no-till practices increased from 36% to 45%. Widespread adoption of these practices has resulted in a 44% reduction in soil loss per pound of cotton produced on U.S. cotton acreage over the past 30 years (Field to Market, 2016).
To control weeds and diseases, producers were traditionally forced to remove all plant residues and weeds from the soil surface prior to planting, and then continue to cultivate the soil while the crop was growing to control late emerging weeds. While tilling does control some disease and weeds, it also loosens the soil, making it much more vulnerable to wind and rain.
Today, thanks to seed treatment fungicides, herbicides and herbicide-tolerant cotton, diseases and weeds can be controlled without tilling, allowing what is referred to as “no-till” and conservation tillage systems to be adopted. In addition to preventing erosion and increasing organic matter, reducing tillage significantly reduces fuel use and its associated cost to growers.
All plants need mineral nutrients to grow. How those nutrients are delivered can take a variety of forms, including nitrogen-fixing cover crops, manures and soluble fertilizers. While alternative sources to soluble fertilizers may seem like a sustainable solution, relying on them as a sole source of fertility can compromise yields or lead to the leaching and runoff of nutrients. Excess nitrogen is particularly prone to leaching and runoff and has become a water-quality concern for agriculture.
Cotton growers have other options for increasing soil fertility without applying chemicals or minerals. Conservation tillage and no-till are two such options that are known to impact soil carbon accumulation rates – an accepted indicator of soil health. Research is ongoing to help growers better understand how chemical, physical and microbiological properties are affected when soils are managed with conservation practices.
A long-term comparison between conventional and conservation tillage has shown higher amounts of organic matter present in the surface of soils under conservation tillage. In 2015, that research was expanded to evaluate how using a crimson clover winter cover crop influences nutrient accumulation by young cotton plants and the microbes in and around cotton roots when cotton is grown with conventional and conservation management. A more thorough knowledge of how soil management influences these organisms will be useful in designing more nutrient use efficiency cropping systems.
Exploring the effects of no-till on soil health, Causarano et al. (2006) did a literature review of soil organic carbon in the southern U.S. from Texas eastward. They found that no-till cotton production systems without a cover crop had an average increase of 300 pounds of carbon per acre per year, while no-till with a cover crop increased sequestration to 600 pounds per acre per year.
Crop rotation is another practice for improving soil fertility. Crop rotation is practiced by growing different types of crops in a sequence on the same land. Its benefits include nitrogen replenishment, pest mitigation and prevention of pathogen build-up. Upwards of 82% of producers rotate other crops such as wheat, corn and soybeans in their cotton fields (Reed et al., 2009).
In addition to the tremendous progress that has been made in reducing tillage operations and encouraging organic matter increase in the soil, other modern technologies are also being used to detect and manage crop nutrient needs. These “precision agriculture” technologies include Global Positioning System (GPS) receivers, multi-spectral images, and ground-based sensors to map out soil property variations in the field.
Today, almost 63% of U.S. cotton growers indicate that they employ some type of precision technology in their management, with most reporting that they use it for the site-specific application of soil nutrients (Monney et al., 2010). One precision ag approach is to use a ground-based sensor (such as an electrical conductivity, or EC, sensor) to map the variability present in soil type within the field. For example, the Veris Electrical Conductivity Sensor tests soil electrical conductivity and soil texture, a factor which has a major impact on agricultural productivity, including water holding capacity, topsoil depth and nitrogen use efficiency.
The result of soil EC measurements is a detailed map of soil texture variability that can guide growers’ crop selection and zones. Once the map is created, it is loaded into the fertilizer applicator controller and then each soil type receives only the amount of nutrient that is required in that area of the field. This ensures over-application does not occur and that crop needs are met.
Research is focusing on the use of sensors to detect the condition of the crop and vary the amount of nutrient applied in fields in real time. This eliminates the time spent creating and loading maps, and will provide even greater precision by letting the plant signal its individual needs.