Relationship between leaf area development and P-days in potato varieties under Indian sub-tropics

Abstract

Leaf area is one the essential variables of crop models and the accuracy of its estimate largely determines model performance. It is therefore, necessary to develop mathematical relations that are easy to use and robust so that they are widely applicable under practical field conditions. Leaf area development under stress free situations is mainly temperature dependent. P-days or Physiological Degree Days is a modified form of Growing Degree days (GDD) in which the accumulation of temperature is a function of both maximum and minimum temperatures. In the current investigation, leaf area index (LAI) in six potato varieties with diverse growth habit, duration and yield potential was estimated from the trials undertaken in two distinct sowing windows during three successive years at Patna under the Indian state of Bihar. Leaf Area was recorded at 10 days intervals starting from 30 days after planting (DAP) up to 90 DAP and empirical relations were developed between LAI coefficient versus accumulated P-Days. P-days were calculated with minimum, optimum and maximum threshold values of air temperatures viz., 7°C, 21°C and 30°C, respectively. Results from the above growth analysis undertaken for three successive years with two distinctly different planting dates in Indo-Gangetic Plains revealed that development of LAI in potato was related to P days for different potato varieties with diverse growth duration. The Pm (at which the maximum LAI was attained) was 380.9 for the first date of planting, while it was 363.9 for the second one (date of planting) in all the varieties except Kufri Sindhuri where it was 483.5 and 455.5 in the first and second date of planting, respectively. The following relationships for short (1), medium (2) and long duration (3) potato varieties under normal planting season adequately described LAI development under Indian subtropics: 1) LAI =4.4/{1+exp (3.2356-5.7742 x P/380.9)} for Kufri Pukhraj (R2=0.93); 2) LAI =4/{1+exp (3.37-5.7943 x P/380.9)} for Kufri Lalima (R2=0.90); and 3) LAI =3.9/{1 +exp (3.3768-6.1463 x P/483.5)} for Kufri Sindhuri (R2=0.96); and where P is the accumulated P days with 70C, 210C and 300C as the minimum, optimum and maximum temperature thresholds. These relationships have further scope for use under other stress free conditions for potential leaf area measurements for yield estimation in potato (Solanum tuberosum L.).