Are organic agricultural management practices more or less effective at resisting drought than conventional agricultural practices?

Are organic agricultural management practices more or less effective at resisting drought than conventional agricultural practices?

Introduction

When you walk into the produce or meat sections of your local grocery store it is common these days to see several different types of the same fruits, vegetables or meats/dairy. There will be regular versions of these products and there may be organic, free range, grass feed, or naturally raised versions of these products. To the average consumer these labels mean that the products are “healthier” and that they are grown in a more natural system than the conventionally grown counterparts. While both of these things are true, the label on that USDA organic apple does not show the full picture.

One of the corner stones of organic certification in this country and abroad is the concept that the production system must: improve the quality of the environment in which it operates, conserve the resources present, and minimize inputs and losses, among other concepts. Pimental succinctly states this as “the aim of organic agriculture is to augment ecological processes that foster plant nutrition yet conserve soil and water resources” (Pimental et al. 2005)

 This goal of minimizing the impact to the natural system and taking a holistic approach to agriculture in the hope that it will increase productivity and decrease harm ecologically is accomplished by using a variety of different techniques. Buffer strips of native grasses or forbs are planted along the edges of fields to reduce soil erosion and promote pollinators. Cover crops are planted between seasons or over bare ground during the growing season to improve water infiltration, reduce weed competition, increase soil organic matter, and reduce soil erosion. Rotating crops with legumes after grasses or vegetables reduces soil erosion, reduces fertilizer needs, improves biological diversity and improves water quality. No-till or minimal tillage reduces water loss, reduces soil erosion, and adds organic matter into the system while reducing inputs (USDA 2017).  It is these practices among other that will be the focus of this post.

 I hope to examine the nature of soil health when comparing organically managed agriculture with traditionally managed agriculture and how these changes in soil health effect yields and productivity in drought conditions. After reading through most of the available literature it would appear that factors such as improved OM accumulation, decreased run-off and better ground cover improve water holding capacity of the soil and  decrease evapotranspiration. This in-turn improves yields in non-irrigated agricultural systems during drought or water-stress conditions and decreases the water needs or losses of irrigated agricultural systems. In addition to these topics but not in the scope of this post are other possible factors that are less understood such as soil biology and species diversity.

Body

In the region of the country that I live, the south, water is not a concern for farmers like it is in other parts of the country. In Tennessee water is all around us, it is abundant and availability is not generally an issue like it is in the west. Non-irrigated farms in Tennessee and its neighbors do have issues with short periods of drought during the summer but water is not as much of a regulated resource like it is in other parts of the country and abroad. In California, our nations largest and most profitable producer of agricultural products, water is scarce and seemingly every drop is accounted for by the state. California’s Mediterranean climate means that a huge diversity of crops can be grown there successfully, but the scarcity of water means that the majority of row crops are irrigated in someway. California produces over four hundred different agricultural commodities, one-third of the countries fresh market vegetables, two-thirds of our nations fresh fruits and 11-15% of the nations agricultural production (CDFA 2017). In contrast to this California has been in drought conditions for nearly a decade and 40-60% of the states available water is used for agricultural irrigation (Johnson et al. 2015).  Compared to their eastern counterparts, agricultural producers in the western US have a much more vested interest in protecting and conserving their limited water resources (Pimental et al. 2004).

In developing countries around the world that have arid or semi-arid moisture regimes or seasonal rains, drought and water use are very much a life or death concern. Water shortages leave more than a billion people without adequate drinking water (Pimental et al. 2004).  Agriculture consumes approximately 70% of fresh water world wide. Water usage for agricultural crops is considerable, as shown in Figure 1, around 1000 liters of water are required to produce 1 kilogram of cereal grain (Pimental et al. 2004). Conserving water is critical as global population continues to increase while the amount of fresh water stays the same. Increasing education about soil conservation practices may be part of the solution.

Figure 1: Water usage of crops and livestock (Pimental et al. 2004)

Many practices of organic agriculture focus on soil and resource management. Some of these practices can have a positive benefit on decreasing water use and improving conservation. Erosion and soil nutrient depletion adversely affect a soils ability to hold and intake water. Soil erosion increases water runoff and eroded soils have a run-off rate of about 30 percent (Pimental et al. 2004). Eroded soils also absorb 87% less water than uneroded soils (Pimenatl et al. 2004). By practicing no-till agriculture soil erosion and therefore runoff are reduced (Lal 1993). This practice also increases the accumulation and conservation of organic matter in the soil. Organic matter in the soil is the highly decomposed residue from plants and animals.  This matter aerates the soil and improves the amount of water that is held and can infiltrate into the ground (Pimental et al 2004). High levels of organic matter can increase water infiltration by up to 150% (Pimental et al 2004. Cover crops planted between seasons or along side other crops and crop residues retained when practicing no-tlll farming both aid in water retention by reducing runoff and decreasing evaporation (Pimental et al. 2004).

During times of drought stress well managed soils preform better than others. Lotter and others analyzed relative growth rates and yield of organic and conventional agriculture over 5 drought years between 1984 and 1998 in the northeastern US and found that corn and soybeans grown in an organic system significantly out preformed those grown with conventional methods and also held more water as shown in Figure 2. Water capture of organic plots was approximately 100% higher than conventional plots (Lotter et al. 1990).

Figure 2 Water Content of organic and conventionally managed soils.

With climate change comes changes to relative rainfall and unpredictable drought conditions.

Warming has caused California to experience years of drought and this trend is likely to continue in the future (Diffenbaugh et al. 2015). This increase in drought incidence and the limited nature of water availability in the west means that improvements in the agricultural system will need to be made in order to decrease the amount of water that their agricultural land uses. Intensively managing the soil would significantly improve the health of the ecosystem and allow more water to be available for everything else (Scialabba et al. 2010).  

Warmer, dryer conditions will have a much larger impact on general welfare in rain fed systems in developing countries. These systems use less inputs and yield less than the farming systems used in the united states but the people are much closer to the crops. Droughts in these systems mean that individual families don’t eat. Education on soil management would improve food and water security in these areas. Rainfed managed soils in Zimbabwe had higher soil moisture and greater infiltration than unmanaged soils (Thierfelde et al. 2009).  

Conclusion

Across the planet, as population increases and demand for water and food increase water will become an even more precious resource. The need to properly manage our soils is critical if we hope to feed everyone. Although it is not a complete solution, properly managing and conserving soil will help the water we have go farther and will waste less of it. Climate change and warming trends will have an unpredictable effects on our environment but may cause water scarcity or drought in many areas. Organically managed agricultural systems and soil conserving agricultural systems are shown to hold more water, intake more water, and have less runoff than conventional agricultural systems. By increasing organic matter and conserving plant residues, soil management practices improve the systems water usage. 

Sources:

United States Department of Agriculture; Conservation Choices: Soil Health Practices, https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcseprd1318196.pdf, April 2017

Pimentel, D., Hepperly, B., Hanson, J., Douds,D., Seidel, R.; Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems, BioScience, Volume 55, Issue 7, 1 July 2005, Pages 573–582, https://doi.org/10.1641/0006-3568(2005)055[0573:EEAECO]2.0.CO;2

California Department of Food and Agriculture; California Agricultural Production Statistics, https://www.cdfa.ca.gov/Statistics/PDFs/2016-17AgReport.pdf, 2017

Johnson, R., Cody, R.; Congressional Research Service; California Agricultural Production and Irrigated Water Use, https://fas.org/sgp/crs/misc/R44093.pdf, June 2015

Pimentel, D., Berger, B., Filiberto, D., Newton, M., Wolfe, B., Karabinakis, B., Clark, S., Poon, E., Abbett, E., and Nandagopal, S. 2004. Water resources: agricultural and environmental issues. Bioscience 54 (10): 909-918.

 David Pimentel, Bonnie Berger, David Filiberto, Michelle Newton, Benjamin Wolfe, Elizabeth Karabinakis, Steven Clark, Elaine Poon, Elizabeth Abbett, Sudha Nandagopal; Water Resources: Agricultural and Environmental Issues, BioScience, Volume 54, Issue 10, 1 October 2004, Pages 909–918, https://doi.org/10.1641/0006-3568(2004)054[0909:WRAAEI]2.0.CO;2

Lotter, D., Seidel, R., & Liebhardt, W. (2003). The performance of organic and conventional cropping systems in an extreme climate year. American Journal of Alternative Agriculture, 18(3), 146-154

Diffenbaugh N., Swain D., & Touma D., 2015. Global Warming Increases California Drought Risk. National Acadamy of Sciences. March 2015

Scialabba, N., Müller-Lindenlauf, M., 2010. Organic agriculture and climate change. Renewable Agriculture and Food Systems 25, 158–169.

Thierfelder, C., Wall, P.C., 2009. Effects of conservation agriculture techniques on infiltration and soil water content in Zambia and Zimbabwe. Soil and Tillage Research 105, 217-227.