Soil Organic Carbon Indicator

 أ.د. سيف الدين عبد الرزاق سالم

قسم مكافحة التصحر

Keyword: Soil, Organic carbon, climate change

Introduction:

The Iraqi soil suffers from a decrease in the organic carbon content due to the negative effect of the natural and human factors. Iraq is located in the dry and semi-dry region, which is reflected in the presence of low  natural vegetation cover in semi-wetlands and arid areas. The reduction of organic carbon content has had a significant effect on the general characteristics of the soil, which has negatively affected the productivity of the crop from the agricultural crops under the usual management  methods.

Climate change is one of the major issues affecting all of us on our planet. For the first time in

recorded history the glacier on Africa's Mount Kilimanjaro is melting and the ice at the North Pole had

melted. Another first was recorded in North America - Lake Erie did not freeze over in winter. 2005

recorded the hottest average temperatures on record and produced the most destructive hurricane

season ever. In Greenland the ice is melting three times faster than the early 1990s. Experts from

NASA are predicting that the intensity of major storms will increase even more as a result of rising

ocean temperatures.

Experts expect that climate change will have a negative effect on our food supply due to more

frequent adverse weather events leading to increasing crop failures. The security of our food supply

concerns all of us.

So what has organic agriculture to do with climate change? One of the central tenets of organic

farming is to improve soil health and productivity by increasing organic matter (carbon) levels,

particularly humus.

Published studies show that organic farming systems are more resilient to the predicted weather

extremes. The studies showed that organic systems have higher yields than conventional farming

systems in weather extremes such as floods and droughts. (Drinkwater et al 1998, Welsh 1999).

Importance of organic carbon in soil:

The material is a major part of the Productive soils. Besides improving the physical properties of the soil, it is considered as a storehouse for many of the plant nutrients, especially carbon and nitrogen elements to a large degree, phosphorus, iron and sulfur to a lesser extent. The availability many of these elements in organic form  are affected by the  existence of organic matter due to the many reactions between them.

In general, the soils in a particular area increase their fertility by increasing their organic matter. However, the low soils in their organic content are not always non-fertile. Many  desert soils which is low in their organic content are highly fertile when placed under the farming system. Preserving the content of such soils of organic matter due to its continuous decrease with agricultural practices  unless nitrogen and organic matter are added to it. Microorganisms uses carbon as their source of energy, nitrogen and other elements to build their bodies. Organic matter also has an effect on the aggregation of soil materials and forming  of stable structures, which reflects on its aeration and increasing of water holding capacity, as  well as resistance to erosion. In general, the importance of organic carbon lies in the themes as follow:

First: monitoring the organic carbon content in soils is one of the methods used to monitor climate variability in the world and its impact on the phenomenon of global warming. Soil is a natural reservoir of carbonate gases through biological activity, especially plants that absorb carbon dioxide through Food production, and then accumulate plant waste in the body of soil and turn into different organic materials in degrees of decomposition, so that the soil stores carbon twice or more than what is in the air. Studies have shown that carbon solubility sends about 8.9 giga tons (8.9 x 10 ° ° g) per year of carbonic gases, while the soil storage and one meter depth is about 2400 giga tonnes (2400x10 ° ° g). Studies indicate that the total area of land in the world, estimated at 141 million km 2, contains about 161 tons of organic carbon per hectare . It is noted in developed countries agricultural, working to surround the agricultural areas with a fence of trees in order to protect the soil from the effects of the wind as well Increase carbon storage in agricultural soils and contribute to reducing the concentration of carbonic gases in the atmosphere as shown in Figure 1.

Fig1 .Plant windbreaks

 Second: Effect on soil characteristics directly or indirectly:

1 - help to maintain the moisture content of the soil, especially during the period of drought .

2. Improving of soil structure and soil porosity.

3 - increase the availability of the essential nutrients of the plant.

4 - is a source of energy, which works on the supply of living organisms carbon dioxide.

5 - reduce the erosion of the soil.

Why is carbon important to productive farming?

Soil carbon is one of the most neglected yet most important factors in soil fertility, disease control, water efficiency and farm productivity. Humus and its related acids are significantly important forms of carbon. Below is a summary of the benefits of humus.

Humus improves nutrient availability:

Stores 90 to 95% of the nitrogen in the soil, 15 to 80% of phosphorus and 50 to 20% of Sculpture in the soil

•         Has many sites that hold minerals and consequently dramatically increases the soils TEC (amount

              of plant available nutrients that the soil can store)

•         Stores cations, such as calcium, magnesium, potassium and all trace elements

•         Prevents nutrient leaching by holding them

•         Organic acids (humic, fulvic, ulmic and others) help make minerals available by dissolving locked

              up minerals

•         Prevents mineral ions from being locked up

•         Encourages a range of microbes that make locked up minerals available to plants.

•         Helps to neutralize the pH

•         Buffers the soil from strong changes in pH.

Humus improves soil structure:

•         Promotes good soil structure which creates soil spaces for air and water

•         Assists with good/strong ped formation

•         Encourages macro-organisms (ie earthworms and beetles etc) that form pores in the soil.

Humus directly assists plants:

•         The spaces allow microorganisms to turn the nitrogen in the air into nitrate and ammonia

•         Soil carbon dioxide contained in these air spaces increases plant growth

•         Helps plant and microbial growth through growth stimulating compounds

•         Helps root growth, by making it easy for roots to travel through the soil

Humus improves soil water relationships:

•         The open structure increases rain absorption

•         Decreases water loss from run off.

•         ?Humus molecules soak up to 20 times their weight in water.

•         It is stored in the soil for later use by the plants.

•         Improved ped formation helps the soil stay well drained.

•         Greenhouse Gas Abatement

•         Very importantly organic agriculture can help reverse climate change. Published peer review scientific

•         studies in North America and Europe show that best practice organic agriculture emits less

•         greenhouse gases than conventional agriculture and the carbon sequestration from increasing soil

•         organic matter leads to a net reduction in greenhouse gases. (Drinkwater et al 1998, Mader et al 2002,

•         Pimentel 2005, Reganold et al 2001).

•         Organic agriculture helps to reduce greenhouse gases by converting atmospheric carbon dioxide

•         (CO2) into soil organic matter. Some forms of conventional agriculture have caused a massive decline

•         in soil organic matter, due to oxidising organic carbon by incorrect tillage, the overuse of nitrogen

•         fertilisers and from topsoil loss through wind and water erosion.

Soil organic carbon content:

1. At the global level:

The soils vary spatially in their organic carbon content, from one location to another within the geographical area and from one geographic region to another, as well as within the different topographic sites, depending on the state of variation in the environmental conditions, especially the moisture and thermal content of the soil affecting the vegetation type and density, Organic waste. As shown in Figure 2, the organic carbon content of the soil layer of soil (0-30 cm) at the global level, between 10 and more than 150 tons / ha) is the case of the interaction  effect of many environmental factors.

Figure 2: Spatial distribution of organic carbon content in surface soils of the world (ton / ha).

Second: the soil content of organic carbon:

Iraqi soils are generally low in organic carbon content for a different of reasons, such as natural factors and human factors. Depending on the environmental conditions prevailing in Iraq, Iraqi soil can be divided into three relatively different environmental zones in their organic carbon content, which generally range from less than 10 g / kg to more than 20 g / kg (Figure 3): 

Figure 3: Spatial distribution of organic carbon in Iraqi soils.

1.       The northern regions of Iraq, namely Dahuk, Erbil and Sulaymaniyah, are characterized by a semi-humid climate (rainfall average of more than 800 mm) and a vegetation cover ranging from forests, grasses and prevailing of rainfed  agriculture in the region . This has helped to increase the relative organic carbon content Surface (0-30 cm plow) to cultivate the area, which is often more than 2.0 g / kg.

2.       The transitional area represented by the provinces of Nineveh and Kirkuk and parts of the province of Diyala, where the predominance of complementary agriculture because of the low amount of rain falling at rates ranging from 200 to 400 mm with the dominance of grass plants and agricultural crops and low densities, so the organic carbon content in the soil of that region ranges from 10 to 20 g / kg.

3.       The rest of the land in the other central and southern governorates is characterized by low organic carbon content (generally less than 10 g / kg) due to the dry climate and low density of vegetation cover, which helps the rate of adding organic waste to a very high Organic waste is lost as a result of increased degradation processes. It should be noted that the marshlands and marshlands in the south of Iraq are different because of the difference in the environmental situation prevailing in those sites, which helps the accumulation of organic waste in the soil, which helps to increase the organic carbon content in their soil and reaches more than 20 g / Kg.

Factors affecting the organic carbon in the soil content:

 First: Natural factors:

1-       Type and density of existing plants: The soils under leafy trees in a cold atmosphere receive their organic matter from those falling leaves, which are concentrated in the upper layers or in the first centimeter of the soil. The soils under the grassland are derived from the dense fibrous roots distributed regularly in the soil  profile and with depth is too large to some extent.

2 - drainage and soil aeration condition

In general, poor drainage leads to accumulation of ground water to the level at which soils become saturation, which helps to increase the accumulation of organic matter due to the low degradation and loss of organic waste.

3. Climate (rain and heat):

In general, the amount of organic matter increases as the annual rainfall rate increases in the region resulting  increase in plant growth by increasing the rainfall rate, so that the quantity of organic matter is low in the wetland soils. Low temperatures also help to build up organic matter, while higher average of temperatures reduce their amount in soil. This is due to the effect of heat on increasing the speed of chemical and biological reactions occurring when organic matter is degraded. In addition, poor drainage soil , is generally high in organic matter and nitrogen when compared to well-drained soil. The lack of aeration in poor drainage soils is responsible for accumulation of organic matter and nitrogen. It is necessary to mention the impact of plowing and the water or wind erosion of the soil surface layer,  the amount of organic matter in the soils are reduced by about 30-6% in the soils not exposed to tillage and, pasture lands , forests . The erosion of surface soil would eliminate a large proportion of the organic matter accumulated in the soil.

4- Soil type:

The amount of organic matter varies considerably between the different types of soils, while its amount on the surface layer consider traces in some  mineral soils, may not exceed 15%  under special conditions. In general, it find that coarse soils texture contain less organic matter regarding to  fine soils because of  the  density of plants growing in coarse texture  soils is less  and have good aeration condition, which lead   for rapid oxidation of organic matter and good soil infiltration rate.

Topographic:

 In the flat soils, an accumulation  of organic matter occurs more than those on the slopes due to the erosion effect in the displacement of the surface layer of the land on the slopes. In the depressions where the drainage is determined, the decomposition rate is slow and  accumulation is increased under  cold   humid conditions . Accumulation increases under cold and humid condition where the growth rate  high and conditions are not encourage  to decomposition processing , resulting accumulation  in large amounts of humus, while under humid hot condition , slightly accumulation occurs due to the increased decomposition rates. Generally , any increase in temperature by 10 ° C leads to a reduction of the soil organic matter by a half or one- third.

Second: Human Factor: The human factor plays a large role in determining the soil content of organic carbon through the methods of  soil managements. Studies indicate that the organic carbon content in soils can decrease or increase depending on the processes used in the management of the soil. From Figure 4, the state of time variation in the organic carbon content of soils is observed according to the type of management processes of the soil.

Figure 4: Effect of practices managements  on organic carbon content in soil

The applied studies related to the effect of the soil management practices  methods used for the  agricultural purposes and for long periods of time indicate that there is a difference in the amount of organic carbon added to the soil depending on, the nature of the type of management practices used. The results in the table indicate that the use of soil for planting forest plants is liable  to add About 0.6 tons / ha per year of organic carbon to the soil, while the  agricultural cycle method used ,led to the addition of about 0.2 tons / ha per year of organic carbon.

Table1. Effect of management  practices on the amount of organic carbon added to the soil.

Challenges Increase organic carbon content in Iraqi soils:

Soil is generally characterized by the of low in organic carbon content, which ranges between 10 g kg-1  in the surface horizons of most of the soils to more than 30 g kg -1 for some soils, especially in the northern part of Iraq and some marshland  in southern Iraq. That the increase or preservation of organic content in Iraqi soil requires the competent authorities to apply the scientific and administrative principles accompanying all types of uses of the soil, especially agricultural, which can be limited to:

1.       Preserving natural vegetation cover and not remove from the soil surface  and    work to increase the density of green areas, whether wood or grasses

2.       avoiding   overgrazing method .

3.       use  of zero  tillage methods, especially in rainfed areas.

4.       use of conservation agriculture.

5.       Application of the  agricultural rotation, especially legume crops.

6.       Addition organic waste of various kinds.

7.       overturn of the residual of previous crops and the non-adoption of methods of burning.

8.       Use appropriate irrigation methods to help maintain appropriate soil moisture contenting.

Use plants to grow soil carbon

1.       The most economical and effective way to increase soil carbon is to grow it.

2.       Plants get between 95 and 98% of their minerals from the air and water. If we look at the chemical

3.       composition of an average plant, Carbon, Hydrogen and Oxygen account for over 95% of the

4.       minerals. The remaining 5% or less come from the soil.

5.       These minerals are combined using the energy of the sun via photosynthesis to produce the carbon

6.       based compounds that plants need to grow and reproduce.

References:

Drinkwater, L. E., Wagoner, P. & Sarrantonio, M. (1998), Legume-based cropping systems have

reduced carbon and nitrogen losses. Nature 396, 262 - 265 (1998).

Reganold, J. P. et al (2001). Sustainability of three apple production systems. Nature 410, 926–930.

Rodale (2003). Farm Systems Trial, The Rodale Institute 611 Siegfriedale Road Kutztown, PA 19530-9320 USA.