Organic vs Inorganic Nutrients: A Primer on Plant Nutrition

Farmers, manufacturers, and consumers are all exposed to buzzwords such as organic or synthetic, natural or chemical, and other such comparisons when talking about the way crops and plants are grown, and eventually, advertised in the market. But what difference between inorganic and organic nutrients should you pay attention to, and what benefits and drawbacks are there for each option? Let’s examine the basics.

1 . Background

Plant nutrients

Plants need sunlight, air, water, and soil to grow. While these four are essentials, they aren’t really what the plants need, per se. Rather, it’s the elements (i.e., elements in the periodic table) contained in these sources that plants need to process to grow.

The minimum concentrations of plant essential nutrients required for growth vary from species to species. However, the list below (based on Biology Reference) presents general nutrient requirements, with some needed in bigger quantities while others may be used optionally.

The 14 essential plant nutrients

Between macro- and micro-nutrients, one nutrient element is not more important than another, just different quantities and concentrations are needed for each one of them.

  • Macronutrients (elements required in greater quantities):
      • N (Nitrogen): for the development of nucleic acids, some hormones, and chlorophyll.
      • K (Potassium): enzyme activator, involved in starch formation; regulates osmotic balance and movement of guard cells.
      • Ca (Calcium): controls activity of many enzymes; maintains membrane integrity and acts as a messenger. 
      • Mg (Magnesium): Component of chlorophyll and activates many enzymes. 
      • O (Oxygen): Component of organic compounds and water; electron acceptor in respiration.
      • S (Sulfur): Components of amino acids’ cysteine and methionine; component of coenzyme A.
      • H (Hydrogen): Components of organic compounds and water; chemiosmotic synthesis of ATP in mitochondria and chloroplasts.
      • C (Carbon): Components of organic compounds.
  • Micronutrients (elements required in smaller quantities):
      • Cl (Chlorine): involved in water balance; possibly involved in photosynthetic reactions where O2 is released
      • Fe (Iron): component of cytochromes ferredoxin and nitrogenase; cofactor of peroxidase; involved in chlorophyll synthesis
      • B (Boron): could help with sugar transport; regulates enzyme function
      • Mn (Manganese): Activator of enzymes; involved in electron transfer, chlorophyll synthesis, and the photosynthetic evolution of O2
      • Zn (Zinc): Activates many enzymes; involved in the formation of pollen
      • Cu (Copper): Component of plastocyanin; present in lignin of xylem elements; activates enzymes
      • Mo (Molybdenum): Involved in nitrogen reduction
      • Ni (Nickel), Si (Silicon), Na (Sodium): considered essential only for some plants

    Depletion or shortage of nutrients could indicate that the crop will not be able to maintain its leaf growth or maintain further development. Either of these will have effects on crop growth and the production of agricultural products. Plant species differ in their degree of responses to nutrient sources (Akanbi et al 2010). Also, crop varieties have been reported to respond differently to applied nutrients. In an experiment on the response of wheat varieties to organic and conventional fertilizers, it was observed that crop demand for and the form of nutrient used by crop varies and this depends on nutrient sources, soil conditions, crop root biomass, and its absorption rate (Lombin et al; 1991, Akanbi et al 2000).

    Plant nutrients acquisition

    Both aboveground and belowground interactions of plants with their immediate surrounding contribute to how plants accumulate macro and micronutrients needed to function. While the basic processes of nutrient absorption by plants is biologically ingrained, people tending crops aim to help plants acquire the right nutrition at the right amounts.

    This is where the debate begins with organic and inorganic nutrients. While the word nutrients could mislead some people into thinking that the concern is mainly about the vitamins, minerals, and essential elements, really, what “organic” and “inorganic” nutrients refer to is the way we feed these vitamins and minerals into the plant.

    In industry-speak, organic and inorganic nutrients are the actual types of inputs added to the plant to amend nutritional requirements. Simply, they are “fertilizers” that are either organically-sourced or synthetically-derived. And whether natural or chemical fertilizers are used, plants do not discern between nutrients derived from the type of fertilizer (organic or otherwise). However, using one or the other entails practical considerations and consequences, economically and with biodiversity.


    2 . Discussion

    Plant nutrients availability

    Organic nutrient sources (Organic fertilizers)

    How to define organic nutrients? According to the Food and Agricultural Organization of the United Nations (FAO), organic nutrient sources are often described as manures, bulky organic manures, or organic fertilizers.

    Most organic nutrient sources, including waste materials, have widely varying compositions and often only a low concentration of nutrients, which differ in their availability. Some of these releases nutrients slowly while others decompose rapidly and release nutrients quickly. However, the effect of organic nutrients nutrition crop yield is long term and not immediate, thus, farmers are reluctant to use organic fertilizers in their cropping system (Khaliq et al 2006).

    Consequently, it has often been pointed out that the use of organic fertilizers may compromise crop yield as compared to inorganic fertilizers because of the reduced input of readily available plant nutrients and the absence of rapid and short-term beneficial effects on microbial and biochemical properties (Pimentel et al. 2005).

    It has been found that organic fertilizers are very safe for human health and the environment. It is made by recycling organic material as plant and animal waste, and food scraps in a controlled process. It has been found that compost enhances the environmental sustainability of agriculture by decreasing chemical inputs and increasing soil organic matter (Mathur et al., 1993). It is used to improve soil properties, water retention capacity, draining, pH, and better availability of soil microorganisms (Khandar and Nigam, 1986; Herrera et al., 1997).

    One notable effect of organic fertilizer is that it contributes to soil health. Because of its high organic material, natural fertilizers are great at increasing both the water-holding capacity and cation-exchange capacity of the soil, stimulating microbial activity and improving soil structure. Organic materials hold great promise due to their local availability as a source of multiple nutrients and ability to improve soil characteristics (Ahmed et al 2011).

    Inorganic nutrient sources (Fertilizers)

    What nutrients are inorganic? By FAO’s definition, fertilizers are, by default, manufactured-sources of nutrients for plants. 

    Fertilizer can be defined as a mined, refined, or manufactured product containing one (straight fertilizers) or more (complex/compound fertilizers) essential plant nutrients in available or potentially available forms and in commercially valuable amounts without carrying any harmful substance above permissible limits. 

    So what are inorganic nutrients? Technically speaking, organic fertilizers are not yet covered by the term fertilizers due to tradition and lower nutrient content compared to fertilizers. However, it is common to associate the words synthetic, mineral, inorganic, artificial, or chemical to describe fertilizers. These terms, as used in conjunction with fertilizers, have a variety of inorganic fertilizers examples available, which are finished products derived from natural deposits produced synthetically (i.e., synthesized in chemical factories). 

    Fertilizers have significant effects on food production in the world, and are an indispensable component of today’s agriculture, with at least 60% of humanity owing its nutritional survival to fertilizers (Fixon and West, 2002). Unfortunately, recovery of essential nutrients (such as nitrogen) in soil-plant systems seldom exceeds 50% of the applied fertilizer, while the remainder is lost (Abbasi et al., 2003).

    This means that the additional inputs from inorganic fertilizers are not retained in the soil, nor does it accumulate over time. The long-term integrity of natural soil composition and health, as well as microbial plant-soil interactions, gets weaker and weaker with an escalating need to use (and eventually, dependence on) fertilizers overtime. Besides, the use of chemical fertilizers alone does not sustain productivity under continuous intensive cropping (Benbi et al., 1998). Consequently, there are growing concerns about the environmental consequences of excess fertilizer use and its future costs.

    Chemical fertilizers are an important input to get higher crop productivity, but over-reliance on chemical fertilizers is associated with a decline in some soil properties and crop yields over time (Hepperly et al., 2009). 

    Despite the poor, physical, and chemical conditions of soil cropped by many farmers, using readily available inorganic fertilizers is the most convenient way for many to enrich soils for planting.

    Organic nutrients vs inorganic nutrients

    Optimum crop performance is usually limited by the inadequate availability of essential nutrients. When a nutrient is available in the right proportion, the photosynthetic activity of the plants will be considerably favored. 

    The application of fertilizer has been reported to significantly increase growth and fruit yield in certain plants. This was attributed to the fact that a sufficient supply of nitrogen will improve cell division and multiplication, foliage production, and photosynthetic activity of the plant. With the current environmental conditions, reasonable crop yield can hardly be achieved without the use of fertilizer (El-Ghamry et al., 2009). 

    Increasing the sustainability of cropping systems involves the reduction of agrochemical and fertilizer inputs through the reliance on soil ecosystem processes and biological interactions for the provision of plant nutrients (Drinkwater and Snapp 2007). Of particular importance are soil microbial processes as they are crucial for plant nutrient supply given their central role in soil organic matter decomposition and nutrient dynamics (Paul 2007). Management of soil fertility through organic fertilizers has always been a pivotal principle of sustainable agriculture. Yet, the impacts of these fertilizers on soil microbial community structure and function as well as on nutrient availability can vary widely, having extremely different impacts on crop productivity (Chivenge et al. 2011). 

    Incorporation of organic fertilizers can also increase microbial activity in soils compared to inorganic fertilizers. Organic fertilizers typically increase soil microbial biomass through the supply of carbon-rich organic compounds to the generally carbon-limited microbial communities in arable soils (Knapp et al. 2010).

    However, there is a growing number of evidences that evaluates the effect of integrated use of organic and inorganic fertilizers with effective microorganisms on the yield and nutrient uptake of plants (Ali et al., 2019). Experiments show that higher yield attributes might be due to higher levels of inorganic fertilizers which increases the activity of photosynthesis and enzymes responsible for the transformation of energy, carbohydrates, fat metabolism, and respiration of plant. Organic manures, on the other hand, act as a slow-release source of nitrogen which improves the nutrient use efficiency of plants (Becker et al., 1994). Therefore, inorganic fertilizers in combination with organic manures can result in higher yield (Barik et al., 2008).

    High-yielding crops that require high amounts of nutrients benefits the most from the readily available form of nutrients provided by inorganic fertilizers as the use of organic manures alone might not meet the plant requirement for growth. But to maintain good soil health, it is necessary to use organic manures in conjunction with inorganic fertilizers to obtain optimum yields in the long-term (Ramalakshmi et al., 2012).


    3 . Conclusion

    Using inorganic fertilizer has been an indispensable part of crop cultivation in many parts of the world since it was first introduced in the market in the latter half of the 19th century. Nutrient requirements at the amounts and availability demanded of modern agriculture means that chemical fertilizers are the most convenient form of plant nutrition source for many. Similarly, with state-of-the-art advancements in farming, artificial fertilizer is a must for certain methods such as some indoor vertical farms and in hydroponic farming (farming that depends on a liquid nutrient solution instead of soil).

    Contrary to the detrimental effects of inorganic fertilizers, organic fertilizers have ecosystem-wide benefits as it improves soil health resulting in enhanced crop yield. However, the use of organic manures alone might not meet the plant requirement.

    Therefore, in order to make the soil well supplied with all the plant nutrients in the readily available form and to maintain good soil health, it is necessary to use organic manures in conjunction with inorganic fertilizers to obtain optimum yields (Ramalakshmi et al., 2012). Results have also shown that integrated nutrients management increases the yield and nutrient uptake (Mohanty et al., 2013). The efficiency of nutrient use may be raised by the combined use of organic and inorganic nutrients. Organic fertilizers not only act as the source of nutrients but also provide micronutrients and modify soil-physical behavior as well as increase the efficiency of applied nutrients (Pandey et al., 2007). 

    The higher yield associated with a higher level of inorganic fertilizers in combination with organic manures may be due to its greater availability and uptake of macro and micro-nutrients and active participation in carbon assimilation, photosynthesis, starch formation, translocation of protein and sugar, entry of water into plants root and development, etc. (Kumar et al., 2014). Studies confirm that besides increasing the crop yield, such practices save mineral fertilization which has potential effects on sustainable agricultural production in soils low in organic matter. In addition, the possibility of sustaining the soil ecology and the environment cannot be ignored.

    Producers and consumers alike serve to benefit from knowing the right macro- and micro-nutrients plants can uptake. When using organic nutrient sources or inorganic ones (or used together), remember that there are economic and environmental pros and cons with using fertilizers to achieve desired yield quantity and quality.

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