Soil fertility supplements

In spite of proper soil organic matter management, application of farm-made or commercial organic or mineral fertilizers may be recommended to overcome distinct nutrient defi ciencies. Deficiency may be due to unbalanced soil pH or slow release of nutrients from an organic source. Dry soil conditions or cold soils in high altitude may intensify the problem. Before choosing a specifi c fertilizer, farmers should know the reason for the problem. Use of external fertilizers should only be the last step of an integrated approach soil fertility and plant nutrition. Reliance on the wrong fertilizer may be a waste of money. In case of signs of nutrient defi ciency or slowed growth farm-own liquid organic fertilizers may boost plant growth. Such liquid fertilizers are simple to make and are available free of cost.

Natural liquid fertilizers

Liquid fertilizers are helpful to overcome temporary nutrient shortages and to stimulate plant growth. They can be made of animal manure, compost or green plant material. Liquid manures are made from animal manure and compost tea from ripe compost while plant tea is made from nitrogen rich plant materials. Liquid manures and plant tea are both a quick source of nitrogen, while compost tea is a nutritionally more balanced general fertilizer.
Liquid fertilizers are mostly used in vegetables, but can also be used for grains and other crops. Although all these liquid fertilizers may be made in the same way, manure tea is not generally recommended as foliar spray, but for application around the base of the plant. In case liquid manure is applied to the leaves in vegetable crops intended for raw consumption, a pre-harvest interval of at least 100 days is needed to avoid the risk of transferring human and animal pathogens.
Application of liquid fertilizers to the leaves is an interesting option in case of nutrient defi ciencies, as plants absorb nutrients about 20 times faster through the leaves than through the roots. Besides promoting crop health and productivity, liquid manures that are applied to the leaves can also act as a good repellent for sucking insects, and may distort life cycles of some sap-sucking insects at the egg stage. They can also interfere with fungal spores.

Procedure for making plant tea

To make plant tea, nutrient rich material is soaked in water for several days or weeks to undergo fermentation. Frequent stirring encourages microbial activity.
The resulting liquid can either be used as a foliar fertilizer or be applied to the soil.
How to make plant tea:

Chop the green plant materials like tithonia, velvet bean or any other sappy material, and put in a drum or any sizeable container until it is about three-quarters full. Fill with water and keep it under shade or cover to prevent excessive evaporation.
Stir every three days and the mixture will be ready to apply in about 15 days.
Remove the remains of the plant material, sieve the mixture and dilute the tea with 2 parts water for every 1 part of tea. Apply the diluted mixture as a top dressing, giving between ½ to ¼ litres per plant for as long as needed. Cover the remaining undiluted mixture in a cool place.

Procedure for making manure tea

Fresh manure from cattle, chicken, goats, sheep, rabbits or a mixture of any of these manures can be used. The procedure for making good manure tea is as follows:
1. Fill a bag with about 50 kg of manure and tie it securely with a rope. Hang the bag with the manure to a pole placed over a 200 litre capacity drum to allow it to suspend into the drum, then fi ll the drum with water.
2. Cover the drum with a polythene sheet to prevent nitrogen from escaping and let it stand under shade.
3. Stir the mixture in the drum every 3–5 days by partially lifting the bag in and out of water several times using the pole.
4. After 2–3 weeks, the water will have turned dark and most of the nutrients will have been dissolved into the water. The darker the colour, the more concentrated the mixture. It is then ready for use. Remove the bag with manure remains from the drum and the water solution is ready to dilute for use.
5. Dilute the manure tea with 2 parts of water for every 1 part of tea. However, if the manure tea is very concentrated (very dark) use 3 parts of water to every 1 part of tea.
6. Apply the manure tea to the crops, giving between 1/2 to 1/4 litres per plant starting 2–3 weeks after planting. Apply the manure tea around the stem and not on the leaves. Repeat the application every 3–4 weeks. Avoid application at full sunshine because of high risk of leaf burns and nutrient losses. Apply in the early morning or on cloudy days.

Application of compost tea

Compost tea can be used unfiltered by applying it directly to the soil area around a plant.
If it is used as a foliar spray, it must be strained tea through a fine mesh cloth first and diluted with good quality well or rain water at a ratio of 10 parts water to 1 part tea. The color should be that of a weak tea. Addition of 1/8 tablespoon of vegetable oil or mild dish-washing liquid per gallon helps the spray adhere to the leaves.
Application to the leaves should not be done during the heat of the day. Early morning or a cloudy day is best. Re-application is necessary after it rains.

Proposed Group Exercise: Commercial organic fertilizers

Ask the farmers to generate a list of commonly available commercial organic fertilizers in the region. Discuss some farmer experiences of using them and the results obtained.

Commercial fertilizers for organic farming

Based on the IFOAM Norms for Organic Production and Processing application of commercial fertilisers (including lime) is allowed in certified organic agriculture with some restrictions. While synthetic fertilizers such as urea are not permitted, use of commercial fertilizers should be justified by recommendations from soil or plant analysis. They must only be applied in their naturally occurring form and used in combination with other techniques such as addition of suitable organic matter, green manures, crop rotations and nitrogen fixing plants.
There are different commercial fertilizers available on the market that are produced from natural substances and do not contain chemical residues. To most African farmers, however, commercial organic fertilizers are not easily accessible mainly due to economic and physical barriers. They also tend to be quite expensive. Therefore, such fertilizers should only be used where using green manure and application of compost is not feasible or have not supplied sufficient nutrients for the crops, or where the crops show specifi c defi ciency symptoms. In certified organic farming, it is the responsibility of the farmer to inquire from fellow organic farmers, trainers or certifying agents, whether a particular fertilizer is natural or not.
In many areas with the capacity to add lime in the case of acidic soils and sulphur in the case of alkaline soils, a conventional approach would be possible even if it did not represent the best solution. But considering constraints African farmers have to access fertilizers in general, large-scale liming or sulphuring appears to be an unsustainable approach to solve the problem. Thus, as a general rule, commercial organic fertilizers should be mixed with other organic materials from the farm or composted together.
The East African Organic Product Standards (2007) permit the following fertilizers of mineral origin for East African organic farmers: basic slag, calcareous and magnesium amendments, limestone, gypsum, marl, maerl, chalk, sugar beet lime, calcium chloride, magnesium rock, kieserite and Epsom salt (magnesium sulphate), mineral potassium (such as sulphate of potash, muriate of potash, kainite, sylvanite, patentkali), natural phosphates, pulverized rock, stone meal, clay (such as bentonite, perlite, vermiculite, zeolite), sodium chloride, and sulphur. This list excludes Chilean nitrate.
Farmers are encouraged to consult with their extension agents or certifying agents before using any of these fertilizers as specific conditions might differ.

Commercial organic fertilizers

Commercial organic fertilizers are mostly by-products of agro-processing and food industrial waste. Examples include seed oil cakes (soybean, sunfl ower, neem, peanut), pelleted chicken manure, and agro-processing by-products such as brewery, fruit peels, coffee husks, wood shavings and dust, rice husks and plant ashes. Others include bone meal, feather meal, fi sh meal, horn and hoof meal, as well as commercially produced composts.

Commercial mineral fertilizers

Mineral fertilizers allowed in organic farming are based on ground natural sources and include lime, stone powder, rock phosphate, gypsum, potassium magnesium sulphate, sodium nitrate, vermiculite and other natural reserves like bat guano.

Microbial fertilizers

Microorganisms play an important role in the soil in providing nutrients to plants. Some microbes add nutrients to the soil through mineralisation. Others add nitrogen by fi xing it from the atmosphere. These include Rhizobium, Azospirillum, and Azotobacter. Other microbes, such as Mycorrhizal fungi, help to supply plants with phosphorus. Pseudomonas species are a diverse group of bacteria that can use a wide range of compounds that plants give off when their roots leak or die. They are able to solubilize phosphorus and may help to suppress soil-borne plant diseases.Some farmers and companies may recommend the application of microorganisms to the soil to enhance decomposition processes and control diseases. These microbial fertilizers are usually sold as ready-to-use products for application as sprays or with irrigation water, or for mixing with compost. These products contain living microorganisms and need to be stored and applied cautiously. Microbial products should be used before their expiry date. It is recommended to fi nd out the effect of these products fi rst by testing them on a small-scale and comparing results with the untreated plots.
Microbial fertilizers cannot substitute appropriate soil management practices on the farm. Most bacteria, fungi and other microorganism are naturally present in the soil and can be enhanced by proper application of compost.