Maintenance of soil organic matter and its long-term effects
Lynn Brandenberger, Professor of Horticultural Food Crops, Oklahoma State University, and Ajay Nair Associate Professor of Extension Vegetables, Iowa State University, discuss the importance of soil care for crop production, especially as it relates to organic matter of the ground
Why should people be interested in being soil keepers? Whether we have a vegetable or animal diet, the soil is at the origin of everything. Feeding the soil to feed the plant is a basic principle of the sustainable agricultural system. Therefore, it is incumbent upon us to be good stewards of the soil to secure future food and fiber supplies. When food and fiber supplies are scarce, societies do not survive long and life can easily slip from semblance of order into chaos.
Soils are the foundation of our food production system while providing other essential services related to water, air and climate. Soils are made up of inorganic and organic materials in a matrix that also includes materials in liquid and gaseous form. The inorganic comes from the rock (parent material) which eventually weathers into what we think of as soil particles (sand, silt, clay) which determine the texture of the soil. There is not much we can do to alter the texture of the soil, which means that in the field the percentage of sand, silt or clay in the soil will more than likely remain unchanged. Organic matter comes from plants, microflora (fungi, bacteria, protozoa) and animals. Soils serve as a carbon bank in that some have estimated that globally, soils hold four times more carbon in the environment than living plants (Magdoff and Van Es, 2009).
Soil organic matter is one of the main indicators of soil health and is fundamental to the long-term sustainability of agroecosystems (Larkin, 2015). Organic matter (OM) can modify the physical, chemical and biological characteristics of soils.
OM additions can increase biological activity in soil to improve plant nutrient availability (OM mineralization), detoxify soil pollutants (bioremediation), increase soil particle aggregation which in turn increases water uptake and storage, and it can improve soil condition (workability). Organic matter is constantly mineralized by soil microbial life and as such, crop growers should consider that additional OM will need to be added regularly to maintain the carbon balance in the soil. Intensive agricultural production practices are not conducive to the preservation of OM and soil quality as they can lead to soil erosion, soil organic matter (SOM) depletion, soil structure deterioration , increased greenhouse gas emissions, biodiversity losses and lead to poor soil quality and reduced harvests. yields (Stavi et al., 2016). Much has been written about the loss of productive agricultural soils to erosion, loss of organic matter and losses due to urbanization. Soils that have been overgrown and damaged can be recovered by adding organic matter, so it is possible to regenerate soils that have become unproductive.
There are a wide range of sources to consider when adding organic matter to improve soil fertility, quality and health. Each farm has its own soil types, sources of organic matter, and equipment for applying and incorporating OM. Decisions should be based on cost, availability, convenience, and generally what works best for a particular farm. Sources can range from compost, manure, animal litter to cover crops and other plant matter. A potential issue for sources is whether the material being considered for use may contain herbicide residues. This is especially true when using grass hay, grass clippings, or compost made from either if they have been treated with herbicides. A simple bioassay using a sensitive species such as tomato or spinach to test for the presence of herbicide residues is good practice.
Other factors affecting organic matter selection could include time and space for composting, food safety risks associated with manure-based soil amendments, and storage of materials prior to application. Cover crops are an alternative to the aforementioned MO sources, but consider that growing cover crops will remove field areas from production for the duration of their cultivation. Therefore, there are no clear alternatives for improving soil MO, each should be carefully considered before use. Organic amendments, including manure, cover crops, and compost, help improve soil quality and health because they improve the activity and abundance of organisms that break them down in the soil (Nair and Ngouajio, 2012).
Soil research studies
Research on increasing soil OM may include different tillage systems and adding organic matter to improve the soil. In Oklahoma, we investigated cover crops for soil improvement by comparing different cover crops to a fallow system with no added organic matter. Although the results were not dramatic, we saw a slow but steady increase in soil organic matter levels in the cover crop treatments and a significant decrease in OM in the fallow system. The jury is still out on crop yields, but there is a trend towards higher yields.
Raimbault and Vyn (1991) reported increases in maize yields through crop rotation compared to continuously grown maize with different cultivation practices also varying in yield. Their most dramatic yield differences were recorded for crop rotation combined with a minimum tillage system. A study conducted in western Colorado in the United States reported less erosion, improved water infiltration rates and higher soil water content with conservation tillage methods compared to conventional tillage (Ashraf et al. 1999). In Iowa, cover crop-based conservation tillage systems have been shown to be viable options for organic broccoli and pepper production (Jokela and Nair, 2016).
Studies in Connecticut have indicated that soil organic matter amounts have a direct effect on productivity, with increases in soil OM stocks being directly related to increased productivity (Oldfield et al. 2018). In the UK, Johnston (1986) reported higher yields on soils that received additional organic matter in sandy and silty loams, soils with higher MO had better water holding capacity, increased nitrogen availability and better response to nitrogen fertilizers. body of evidence confirming that the addition of organic matter (manure, compost, cover crops, mulch, etc.) and reduced tillage improve the physical, chemical and biological properties of the soil and increase the organic C stores in the ground. A systems approach to production is needed to identify and understand the importance of the links between producer practices and their implications for crop growth, yield, productivity, soil quality and health, and the environment.
In vegetable production systems, enterprise diversity, farm size and scale, soil type, market and labor demands, and climatic conditions provide opportunities and/or unique barriers to improving the overall sustainability of our cropping systems. Several grower-run professional organizations and societies such as the Soil Science Society of America, American Society for Horticultural Science, International Society for Horticultural Science, Entomological Society of America, American Phytopathological Society, European Society for Soil Conservation and several other soil science societies in Europe, all work to preserve and protect the current agricultural system.
As we move towards our shared goal of building resilient soils, we must recognize that much work is needed to help growers develop and adopt production practices and strategies that improve the overall productivity of their cropping systems without jeopardize economic, social and environmental benefits. sustainability of their communities.
Ashraf, M., Pearson, C., Westfall, D. and Sharp, R. 1999. Effect of conservation tillage on crop yields, soil erosion and in-furrow irrigation soil properties in the western Colorado. American Journal of Alternative Agriculture, 14(2): 85-92.
Johnston AE 1986. Soil organic matter, effects on soils and crops. Land Use and Management, Volume 2, Number 3: 97-105.
Jokela, D. and Nair, A., 2016. Effects of reduced tillage and fertilizer application method on plant growth, yield and soil health in organic pepper production. Tillage Research 163: 243–254.
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Magdoff, F. and Van Es, H. 2009. Building Soils for Better Crops Sustainable Soil Management – Sustainable Agricultural Research and Extension Handbook #10.
Nair, A. and Ngouajio, M. 2012. Soil microbial biomass, functional microbial diversity and nematode community structure affected by cover crops and compost in an organic vegetable production system Applied Soil Ecology 58:45– 55.
Oldfield, EE, Wood, SA, and Bradford, MA 2018. Direct effects of soil organic matter on productivity mirror those seen with organic amendments. Topsoil 423: 363–373.
Raimbault, BA and Vyn, TJ 1991. Effects of crop rotation and tillage on maize growth and soil structural stability. Journal of Agronomy: 83: 979-985.
Stavi, I., Bel, G. and Zaady, E. 2016. Soil functions and ecosystem services in conventional, conservation and integrated farming systems. A review. Agro. To support. Dev. 36:32.
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