soil-fertility
PROTECTING THE LEAF
SOIL FERTILITY
Soil organic matter is important for maintaining soil health and soil structure, reducing soil loss and increasing nutrient and water use efficiency. Organic matter levels should be maintained at, or improved to, a satisfactory equilibrium level for the particular soil type. The organic matter will derive from cleared vegetation in new plantings and leaf fall, prunings and mulches in mature fields. Long term deterioration in soil structure and fertility may result from compaction, particularly under mechanisation, from changes in soil pH, or from build-up of salinity, a possible side effect of irrigation.
Good Practice
Organic Matter
Retain tea prunings in the field. Provide alternate sources of firewood to discourage the use of prunings for fuel.
Manage shade trees to contribute to organic matter (leaf fall and prunings).
Add organic matter on pruned fields where it is very low (vermicompost, manure, plant litter),taking account of the benefits of different sources in respect of nutrients, micro-organisms and water retention.
Consider soil rehabilitation with a prior crop (Guatemala grass, legumes) in areas designated for tea planting and for 2 years before replanting.
Minimise the period of time when there is no ground cover.
Soil Compaction
Soil compaction can lead to waterlogging and poor plant growth due to deterioration in soil structure.
Soil compaction is not an important issue for tea, except where wheeled mechanised harvesters are in use. Compaction should be monitored in such areas.
The use of heavy machinery during land preparation, especially when the soil is wet, should be avoided.
Maintain plant cover on unpaved paths and tractor ways.
Soil pH and Salinity
Tea requires a pH between 4 and 5.5 for good growth.
Do not plant fields with pH above 5.5. Small areas of high pH soil (e.g. hut-sites) should be planted with high-pH tolerant clones in a large planting hole (25cm x 40cm) with sulphur at the
rate of 60g per hole. Hut sites may be indicated by young tea plants showing stunted growth,
crinkled leaves and balling of the roots.
Diagnosis of suitable conditions for planting can be complemented by observation of adjacent tea fields having healthy tea, and the presence of indicator plants such as Bracken ferns (Pteridium aquilinum), Button weed (Borreria princeae) and Kikuyu grass
(Pennisetum clandestinum).
If soils become too acidic (below pH 4), apply lime at the time of pruning, using good quality dolomitic lime if available. Recommended rates should be obtained from local research/advisory services.
Irrigation is unlikely to lead to salinity build up provided that total annual precipitation exceeds
evapotranspiration. The following should be monitored:
- The water table level
- Total Rainfall + Irrigation– Evapotranspiration to ensure that there is net downward movement of water over the full year
- The quality of irrigation water to avoid situations of high sodium build-up which might
adversely affect crop growth.
Potential Areas For Improvement
Review soil compaction levels on the farm, and develop action plans for managing vulnerable areas (e.g. limiting vehicle movements in areas with wet fragile soils).
Review planting and replanting criteria. Are existing organic matter levels sufficient? Is the soil pH within the range (pH 4 to 5.5) for good tea establishment and sustainable growth?
Reduce longer-term degradation by providing wellformed, well-drained and stable tracks and roads (grass, murram or tarmac dependant upon intensity of use).
The soil is a complex living environment and the influence of ground vegetation, biomass return, pesticide and fertiliser use on its health require further research. Methods
of monitoring and measuring soil health have to be developed.
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