Tea on very acidic soil: when 'acid-loving' goes too far

Tea is one of the few crops that prefers acidic soil — the optimal range for tea growth is a soil pH of about 4.5 to 5.5, with 5.0 to 5.5 described as the most suitable.^{[1, 2]}

Because tea 'likes acid', it is easy to overlook soil that has become too acidic. Research on tea plantations found soil pH was significantly and positively correlated with tea yield, and that continued acidification went with falling productivity.^[2]

Signs to look out for are slower growth and weaker flushes on older fields, even though fertiliser rates have not changed.

• Long-term nitrogen fertiliser. Long-term use of nitrogen fertilisers increases soil acidification, speeds up nitrogen loss from the soil and hinders tea growth. Ammonium fertilisers in particular can push tea garden soils further down.^{[2, 3]}
• Aluminium and manganese toxicity. As soil pH falls, levels of aluminium and manganese become toxic, and potassium, calcium and magnesium are lost through leaching. Acid soils have high aluminium activity, which damages roots of most plants.^{[1, 3]}
• Lower nutrient-holding capacity. A soil's cation exchange capacity — its ability to hold nutrients — is lowest in very acidic soils and rises as the pH is raised.^[4]

• Measure pH across the estate. Test each block rather than assuming. Aim to keep the soil in the range tea prefers, not higher.^{[1, 2]}
• Use lime carefully. Lime raised soil pH in tea plantation studies. Because tea itself needs acidic soil, use a lime rate based on your soil test, so you correct excess acidity without overshooting.^[1]
• Add organic fertiliser and organic matter. Long-term use of organic fertiliser helped regulate soil acidification and improved soil microbial and enzyme activity in tea plantations.^[2]
• Review nitrogen sources and rates. Because long-term nitrogen fertiliser drives acidification, avoid applying more than the crop needs and discuss the nitrogen source with your agronomist.^{[2, 3]}
• Re-test after correction. A follow-up test shows whether pH and nutrient levels have moved into the target range.^[4]

NEXGROW is a bio-organic, phosphate-solubilising fertiliser, and tea is one of the crops in its booklet. The booklet describes it as helping improve soil pH (noting that acidity below pH 4.5 can reduce tea yield and quality), increasing soil carbon and fertility, helping reduce nitrogen, phosphorus and potassium losses through its organic matter, and promoting beneficial soil bacteria.

It is an organic input broadcast on the soil, not a substitute for a lime recommendation on strongly acidic land. Rates below are taken directly from the booklet.

Test soil pH on every block before liming or changing your fertiliser programme, and every few years on older fields that have had heavy nitrogen use. Tea's target pH range is narrow, so a measured value matters more than for most crops.^{[1, 2]}