Coffee in South India is cultivated in high rainfall area. The leaching out or loss of calcium and magnesium present in the soil through runoff during heavy rain and continuous use of acid forming fertilizers like ammonium sulphate are few of the major causes of soil acidity. The soil pH indicates whether the soil is acidic, neutral or alkaline and it can be measured easily using pH meter. The pH scale ranges from 0 to 14; the reaction is acidic when the pH is less than 7 and alkaline when it is above 7.0. for the optimum growth of the coffee plants, the pH of the soil should be around 6.2. under extreme acidic and soil (below pH 4.5) are poor in productivity. Lower availability of nutrients like nitrogen, phosphorus, potassium, calcium and magnesium, toxicity from excess of aluminium, manganese and iron, decreased activity of beneficial micro-organisms and increased activity of harmful micro-organisms particularly those causing root diseases and unfavorable physical conditions of the soil etc., are the ill effects of soil acidity.
Liming
Whenever, the soil pH falls below 6.1, it should be corrected buy the application of alkali forming soil amendments or liming materials. Agricultural lime (Calcium carbonate), dolomite lime (Calcium magnesium carbonate), basic slag (by product from steel factories), slaked lime or hydrated lime (Calcium hydroxide) burnt lime (Calcium oxide) are generally known as liming materials. To make the soil acidity using liming materials is very essential and it is one of the important soil management practices taken up regularly in coffee cultivation.
Agricultural lime and dolomite lime are the most commonly used liming materials in coffee plantations. Burnt lime and slaked lime, though more effective in neutralizing the soil acidity and quick acting than agricultural or dolomite lime, are not generally recommended for application to coffee fields as recommended for application to coffee fields as they may injure the tender feeder roots of coffee plants due to their caustic action and also the rapid change that they bring about in the soil environment may adversely affect the soil micro-flora and fauna. The lime required to bring the soil testing laboratory based on pH (active acidity) and lime requirement pH (potential acidity) measurements. So the testing of representative soil samples of coffee estates under low to medium rainfall, once in three years is strictly recommended while it is advocated once in two years to the areas receiving very high rain fall.
Neutralization value of Liming Materials
The calcium carbonate equivalence of any liming materials is a measure of its purity and effectiveness to neutralize soil acidity and also termed as neutralization value of any liming materials is calculated considering the neutralizing value (% NV) of that materials. Neutralization value of any liming materials is calculated considering the neutralizing value of pure calcium carbonate as 100. A good liming material analyses more than 80% neutralizing value. The comparative neutralizing values of the generally used liming materials are present in the following table.
Choice of Liming Materials
The choice of liming material depends on the cost per unit of neutralizing value, purity and fineness. Liming material should be pure with calcium carbonate equivalence (%NV) around 80 or above. For efficient and quick response the materials have to be powdered fine so that they come in contact with the soil particles on application. The agricultural lime and dolomitic lime should be around fine so that 80% of the materials pass through a 60 mesh sieve. Several by products of paper mills and cement factories also contain high amount of calcium. These are also generally suitable when dry, for use as soil amendments. However, their suitability should be ascertained through laboratory analysis. It is very important to note that indiscriminate use of lime in higher quantity is as bad as note correcting the acidity. Lime application in excess reduces the availability of phosphorus and micronutrients. Continuous application of dolomite may hinder the uptake of potassium and vice versa. Therefore it is recommended to get the soil as well as liming materials analysed in the soil testing laboratories of Coffee Board for suitable advice on the purity of liming materials and quantity to be the field.
Time and Method of Lime Application
Liming of the coffee soils can be done at any time of the year except during monsoon period. However, November to February is the ideal period for lime application in the South-West monsoon area while January to March is ideal for North-East monsoon area. For quick reaction it is desirable to apply lime when there is sufficient moisture (60% WHC) in the soil. Liming material has to be uniformly broadcasted in the field and thorough mixing in the soil ensures faster reaction.
Soil Testing for Advisory on Lime and Fertilizer Application
Soil testing is one of the most important tools used to generate precise information on the nutrient status of the soil for making optimum lime and fertilizer recommendations. Coffee Board has set up soil testing units at CCRI, Balehonnur and CRSS, chettalli, kodagu in Karnataka, RCRS, chundale, Waynad district of Kerala, RCRS, Thandigudi, Dindigal District of Tamil Nadu and RCRS, R.V. Nagar/Narasipatnam of Andhra Pradesh to undertake testing of soil samples from planter’s fields to render suitable advisory on nutrients management. The planters can avail this facility through their respective extension offices or by sending the samples directly to respective laboratories. The upper and lower limits of available NPK in soils is given in the following table.
Tips for Drawing Representative Soil Sample
It is important that the soil samples collected should be the field to be tested. No hard and fast rules could be given for the best manner of soil sampling, as each field presents different problems. Few guidelines are given below for proper sampling.
- When the soil and crop growth are uniform, divide the field into blocks of 2 ha(5 ac) each and sample each block separately.
- When the areas within the field the field differ distinctly in growth of plants or appearance of the soil or known to have been manured differently, then divide the field into blocks and sample each block separately.
- Do not collect the soil samples during rainy season. Collecting samples immediately after the harvest of crop and before blossom showers is ideal.
- Select at random 20 spots at the center of 4 coffee plants in each block. Remove surface litter and dig a hole of 22.5 cm (9″) diameter using a suitable tool (crow bar/sabbal) up to 22.5 cm (9″) depth. Scrape the slices of soil uniformly round the hole from top to bottom and collect in a clean bucket from all the spots. Mix thoroughly to get a uniform mixture and collect a composite sample of 1 kg by quartering technique.
- Samples should not be collected from the blocks which are recently limed or fertilized. Do not collect samples from road side, old bunds, and marshy places or near the shade trees.
- Dry the samples under shade and pack in clean polyethylene bags or cotton bags. Label each sample with name of the estate, block name or number, depth of sample and date of collection. When soil is moist the labels inserted into the sample can decompose. So care should be taken to fix a label on the outer surface of the bag and send to the laboratory for analysis.
- Do not use fertilizer/pesticide contaminated bag for packing soil samples.
- Samples drawn from the problem blocks should be labeled separately.
- Give the details of the estate, crop harvested for the last 5 years, elevation, rainfall details, irrigation schedules if any, variety of coffee and age of the bushes in the information sheet (refer appendix 10). Duly filled information sheet should accompany soil sample as it is required to provide fertilizer recommendation.
- Do not send for analysis samples collected long back and stored.
Leaf Analysis
Leaf analysis is another approach used in determining the nutrient availability of the soil and actual nutrient status of the plant itself at the time of sampling. The use of leaf analysis technique is based on the concept that the greater the content of a particular nutrient in the plant, the higher its availability in the soil. The leaf analysis generally suggested in coffee plantations for distinguishing nutritional disorders, identification of sufficiency, or deficiency of nutrients in plants. Thus, analytical results may be used for suggesting corrective measures before the visual nutrient deficiency/toxicity symptoms appear in the leaves. The leaf analysis values established and used to adjust the fertilizer level are presented in table.