(HERALD ZW) Replace leached nitrogen with side-dressing, tobacco farmers told

Replace leached nitrogen with side-dressing, tobacco farmers told
Saturday, 26 January 2013 00:00
Senior Agriculture Reporter

THE Tobacco Research Board yesterday encouraged tobacco farmers to replace leached nitrogen with additional side-dressing without delay once they noticed symptoms of leaching in their crop.

Head of Crop Productivity Services Division, Dr Dzingai Rukuni said it may not be possible to be precise on the amount of nitrogen lost and the amount to be applied because soil textures differ while other factors like the amount of moisture in the soil, permeability of the soil, slope of the land and the amount of nitrogen initially applied must be considered as well.

“It is, however, logical to apply 75kg of ammonium nitrate per hectare using Cup Number 5 per plant or 150kg of calcium nitrate per hectare or use Cup Number 8 per plant, which should be sufficient although deep coarse-grained soils may require more,” Dr Rukuni said.

Dr Rukuni said for December, plantings as much as 300kg per hectare of ammonium nitrate could be added in four applications of 150kg per hectare using Cup Number 8 per plant at weekly intervals.
He, however, said the current growing season had so far been very favourable for tobacco.

The season started late and subsequent to that, most growing regions received incessant rains over a number of weeks, he said.

“Excessive rains within a short period result in leaching of nutrients, particularly nitrogen.

“If leaching rains occur in early growth, the nitrogen can be leached to below the root zone resulting in pale and yellowed plants,” said Dr Rukuni.

Recently, TRB head of field services, Mr Ezekia Svotwa warned that persistent rains would cause heavy leaching of nutrients.

This will present tobacco farmers with other challenges such as heavy weed infestation that would mean extra costs for labour or herbicides.

“Some of the tobacco that is in water logging soils has already started wilting and dying as the roots rot easily in water,” said Mr Svotwa.

“Tobacco cannot tolerate spending a period of 48 hours in water so this means that those farmers in soils prone to water logging will suffer heavy losses.

“I noticed that in the Nyabira area some farmers’ tobacco fields were water logged.”

He said farmers needed to make a lot of technical interventions to save their crop and would have to buy more fertilisers to apply again and replenish the nutrients lost to leaching.

“The rains are washing away most of the nutrients vital for plant growth leaving the leaves yellowing and losing their quality in the process.

“Plants also grow fast and need more suckerides for the control of suckers.

“There is also a high weed establishment rate while ridges designed to promote good drainage may also be destroyed creating more work for the farmers,” he said.