Though the average area under cotton was the highest in Maharashtra, Gujarat and Andhra Pradesh, there is no proportionate increase in productivity in the last three years.
A socio-economic study on Bt cotton commissioned by Bharat Krishak Samaj found that Tamil Nadu had seen the highest yield at 944 kg a hectare with a cotton area of 1.19 lakh ha.
Gujarat and Andhra Pradesh followed with yields of 659.33 kg/ha and 564.33 kg/ha, which have a cotton area of over 20 lakh ha.
Maharashtra, which tops in cotton acreage with 38 lakh ha, registered the lowest yield of 336 kg/ha.
The average yields showed decline mainly because of expansion of crop in marginal lands (shallow soils in rain-fed areas), erratic weather conditions and increased attacks by sucking pests, the study said.
The study tracked the performance of 1,050 farmers and 300 agricultural labourers in the cotton-growing states of Punjab, Haryana, Rajasthan, Maharashtra, Madhya Pradesh, Andhra Pradesh, Karnataka, Tamil Nadu and Gujarat.