Inorganic vs Organic Fertilisers
Nutrients get depleted from soil over time, and fertilisers need to be added to compensate for the loss. Fertilisers are broadly divided into inorganic (chemical) fertilisers and organic fertilisers.
Inorganic fertilisers are manufactured by processing chemical raw materials. Plants absorb nutrients contained in fertilisers through the process of ‘osmosis’, which requires that the nutrients are in mineral (water-soluble) form. Inorganic fertilisers are in mineral form and are readily absorbable by the plants. Inorganic fertilisers are formulated for the type of plant they fertilise and contain one or more of the primary macronutrients, viz. Nitrogen, Phosphorus and Potassium. Examples of inorganic fertilisers are Urea which contains 46% Nitrogen and 18:18:18 that contains the three primary macronutrients (NPK) in equal proportions. For more reading, see NPK Demystified.
Organic fertilisers are derived from natural organic materials, such as plant and animal matter. Examples of organic fertilisers are droppings from cow, chicken and sheep, oil cakes, biological wastes such as animal bones and compost and so on. Organic fertilisers also contain primary macronutrients; in addition they contain other macro and micro nutrients. However unlike the inorganic fertilisers, they are not in mineral (water-soluble) form. The nutrients in the organic fertilisers have to first get converted to mineral form. The micro-organisms in the soil break down organic fertilisers into their constituent elements (NPK etc) into mineral form, so as to be absorbable by the plants through the osmosis process.
The NPK values of common organic fertilisers are given in the table below.
| Sl. No. | Fertiliser Name | NPK Value | Remarks |
| 1 | Cow dung (dry, composted) | 2 : 1 : 2.4 | A good all around manure |
| 2 | Poutry (dry, composted) | 4 : 3 : 1 | Excellent source of NPK |
| 3 | Bone meal | 3 : 12 : 0.3 | High in Phosphorus. Mildly increases soil pH |
| 4 | Fish meal | 4 : 4 : 0.3 | High in Nitrogen |
| 5 | Fish emulsion | 4 : 4 : 1 | High in Nitrogen. Contains trace elements |
| 6 | Neem cake | 5 : 1 : 1.5 | Mixing in small quantities acts as an insecticide |
| 7 | Groundnut cake | 7 : 3 : 2 | Excellent source of NPK |
| 8 | Wood ash | 0 : 1 : 7 | High in Potassium and Calcium. Increases soil pH |
| 9 | Bio-gas slurry | 2 : 1.3 : 1 | Can be given to plants daily |
| 10 | Compost | 1.5 : 1 : 1.5 | Balanced, slow release fertiliser and soil balancer |
Inorganic vs Organic fertiliser: The use of inorganic vs organic fertilisers is a much debated subject. Whether inorganic or organic, plants can absorb nutrients only when they are in mineral (water-soluble) form. The inorganic fertilisers are already in the mineral form and so their nutrient elements are readily available to plants for absorption. However, that is not the case for organic fertilisers. The soil organisms must break down the organic matter and convert their nutrient contents into mineral form to be absorbable by the plants. This is a process that takes few weeks or even months. Thus organic fertilisers are slow release in comparison with inorganic fertilisers. Also, the concentration of NPK nutrients in organic fertilisers is quite low in comparison with inorganic fertilisers, however they provide the secondary macronutrients and micronutrients (trace elements) that are also needed by the plants.
The organic fertilisers stimulate beneficial soil micro-organisms, and also help to improve and stabilise the soil structure. As against this, inorganic fertilisers will cause micro-organisms, including the good micro-organisms that help plants against diseases, to die out. This adversely affects the plants as well as the soil ecosystem.
The pros and cons of using organic and inorganic fertilisers are given in the table below.
| Sl. No. | Inorganic | Organic |
| 1 | In mineral form. Immediately available for absorption | Not in mineral form. Might take few weeks or months |
| 2 | NPK elements in high concentration | NPK elements in low concentration |
| 3 | Trace elements not present | Trace elements present |
| 4 | Excess application may kill plants | Application without composting can kill plants |
| 5 | Kills beneficial micro organisms. Adversely affects soil eco system | Stimulates beneficial soil micro organisms, and helps to improve and stabilise the soil structure |
Micro-organisms in fact constitute the digestive system of nature. When inorganic fertilisers are applied to plants, this natural system is bypassed and plants get fed directly. The scenario compares to a human being fed intravenously, rather than eating food through the normal digestive path. Just as prolonged intravenous feeding can cause stomach to lose its food digesting function, the result of prolonged application of inorganic fertilisers will be to impair nature’s digestive system. Moreover, inorganic fertilisers kill micro-organisms due to their chemical properties, thus resulting in unhealthy soil environment for plants. Though inorganic fertilisers improve the growth and yield of plants in the short term, it is harmful for the soil and environment in the long run.
Which fertiliser is suitable for Bonsai – Inorganic or organic? Bonsai soil is essentially an artificial environment designed specifically for the different plant species. For bonsai soil system, there is very little space/volume from where roots can absorb nutrients. Organic fertilisers are generally safer for bonsais, but the nutrients provided by them may not be sufficient for the healthy growth of plants. Moreover, the release of nutrients is less predictable in the case of organic fertilisers. Inorganic fertilisers have higher potency and balance of nutrients, and also faster release.
Hence, the preferable fertiliser strategy for bonsais would be to use organic fertilisers as primary nutrients, augmented by inorganic fertilisers.
Which fertiliser is to be preferred for Agriculture – Inorganic or organic? ‘Go organic’ is the mantra these days for the foods for human consumption, both from health and ecological perspectives. This implies that inorganic (chemical) pesticides as well as inorganic fertilisers are not to be used in the agricultural process.
There are two entirely distinct elements in the agricultural process that need to be considered: (1) the use of inorganic vs organic pesticides, and (2) the use of inorganic vs organic fertilisers.
(1) The use of inorganic vs organic pesticides: Organic pesticides are generally less effective than inorganic (chemical) pesticides. However, inorganic pesticides have the serious downside that agricultural produces may contain residues of pesticides, and could be harmful to consumers. So, the use of inorganic pesticides at any stage in any form for agriculture is a strict NO.
(2) The use of inorganic vs organic fertilisers: Regarding the use of inorganic fertilisers, the approach and the logic can be different. Whether the fertiliser is inorganic or organic, the plants finally absorb the nutrients contained in the fertilisers in mineral form. In the case of inorganic fertilisers, the nutrients are already in mineral form, and are readily absorbable by the plants. In the case of organic fertilisers, the micro-organisms in the soil convert the constituent nutrients in the organic matter into their equivalent mineral form and make them absorbable by the plants. Inorganic fertilisers have the downside that they cause environmental damage by way of impairment to the soil ecosystem in the long term, whereas the organic fertilisers stabilise and improve the soil structure. The mineral nutrients, whether sourced from inorganic or organic fertilisers, are the same as far as the plants or their agricultural produces are concerned.
If so, are the agricultural produces cultivated with inorganic fertilisers harmful to their consumers? Logically it should not be. Inorganic fertilisers do cause environmental damage, but have the advantages of higher potency and faster release compared to organic fertilisers. Hence the right fertiliser strategy for agricultural farming would be to use organic fertilisers as primary source, augmented by inorganic fertilisers. The environmental damage caused by inorganic fertilisers should be compensated by the ample use of soil stabilisers, such as compost.