Critical period of weed control in summer groundnut (Arachis hypogaea L.) in gangetic alluvial region in West Bengal.

Many disciplines conduct studies in which the primary objectives depend on inference based on a non-linear relationship between the treatment and response. In particular, interest often focuses on calibrationthat is normally used for estimation of an unknown value of an independent variable (X) corresponding to an observed value of a dependent variable (Y) which is functionally related to X. The application of calibration technique on non-linear models is well known in the field of agriculture, specially, in estimation of critical period of weed control (CPWC) of crops. In the present piece of investigation, an attempt has also been made to determine the CPWC of summer groundnut in West Bengal. The beginning and end of CPWC were based on 5% acceptable yield loss levels which were determined by fitting Logistic and Gompertz models to relative percentage yield data, representing increasing duration of weed interference and weed free period, estimated as growing degree days (GDD). The study reveals that CPWC for pod yield of summer groundnut (var. J.L.-24) was between 149.02 and 587.84 GDD in the year 2001 and it was between 153.27 and 718.72 GDD in the year 2002.The weeds should be controlled from the 15 days after emergence and it should be controlled up to 50 days after emergence to avoid losses above 5%.