Get a soil test done before giving Gypsum to sugarcane. Saline soil needs good water and drainage to wash out the salt; Gypsum is not needed. In sodic soil, Gypsum and farmyard manure can help. The two look alike, but the remedies are different, so do not spend on Gypsum without a test.
How to tell the difference?
- Saline soil: Sugarcane leaves wilt early, the tips scorch and growth stops. In severe cases the plant dies.
- Sodic soil: A crust forms on top, water goes down slowly, roots get less air, and fewer nutrients are taken up.
South African Sugarcane Research Institute (SASRI) definition: saline soil has EC above 400 mS/m (4 dS/m) and SAR below 6. Sodic soil has EC below 400 mS/m, SAR above 6 and pH above 8.5. Depending on the soil type, the critical SAR is taken as 6, 10 or 15.
How much effect at what EC?
- 0 to 200 mS/m: no effect on growth.
- 200 to 400 mS/m: slight effect.
- 400 to 600 mS/m: considerable effect.
- Above 600 mS/m: very severe effect.
Salinity mostly increases from poor drainage and too much irrigation, because the water table rises and salt comes up. In a drought year the problem can get worse.
According to SASRI, sugarcane tolerates salts better than maize and soyabean, but as salts increase, yield is affected. For this reason it is better to get a test done before new planting, and not only when salts become visible.
What to do in which soil?
- Saline soil: Start drainage and wash the salt down with good water. According to SASRI, Gypsum or sulphur is not needed. Washing without drainage will not help.
- Sodic soil: Mix Gypsum and well-rotted organic manure into the soil, then wash with water. Keep the dose according to the soil test report and soil advice.
- Irrigation water: Also check the EC and SAR of the water, because salts can change between summer and winter.
- Soil sampling: Take samples from both good and poor parts at depths of 0-30, 30-60 and 60-90 cm.
Navsari Agricultural University study from South Gujarat
In a Navsari Agricultural University study on clay sodic soil in farmers' fields during 2003 to 2005:
- Giving Gypsum + farmyard manure gave 14.1 tonnes / hectare more sugarcane than giving none, and soil pH and ESP fell.
- In paired-row planting sugarcane gave 67.6 tonnes / hectare, and in normal planting 61.2 tonnes / hectare.
- As sodicity increased, growth, yield, nutrient uptake and juice quality fell.
- The CoN 91132 variety withstood sodicity better than the two other varieties tested.
These are results from one study, not a promise. Find out from an agricultural university which current variety suits your soil.
Questions and answers
Should Gypsum be given in every saline soil?
No. According to SASRI, saline soil does not need Gypsum; it needs drainage and leaching with good water. Gypsum is mainly for sodic soil.
What to look for in a soil test?
EC, SAR and pH. Also get the irrigation water tested, and ask the lab which EC method it used.
Sources: SASRI Information Sheet 5.11: Properties of saline/sodic soils and their reclamation · Patel K.G. (Navsari Agricultural University, 2006): Management of clay sodic soils for enhancing sugarcane productivity in South Gujarat
*Farmers' results are their own experience, not a guarantee. Results change with soil, water, weather and care.
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