Harvest index
Procedure of data collection
Data was collected on yield and yield contributing parameters of cultivated different varieties of T. Aman rice. A brief outline of data collection procedure is given below.
Plant height: Plant height was measured in cm from the ground level to the tip of the longest panicle.
Number of effective tillers hill-1: The panicle which had at least one grain was considered as effective tiller.
Number of non-effective tillers hill-1:Only the non-bearing tillers were counted from each sample and then average of five samples was taken.
Number of grains panicle-1: Presence of any food material in the spikelet was considered as grain. Total number of grains of ten randomly selected panicle were counted. Average mean of grains of these ten panicles was taken as number of grains panicle-1.
Number of sterile spikelets panicle-1: Grains lacking any food material inside the grain was considered as sterile spikelet and such grains present on the each panicle were counted.
Thousand grain weight: One thousand clean dried grains were counted from the seed stock obtained from the ten sample plants of each plot and their weight (g) were taken in by using an electric balance.
Panicle length:
Length of panicle was measured from each panicle from the first node to the tip of the panicle and then average five samples was taken & measured in cm.
Grain yield: Grains obtained from each unit plot were sun dried and weighed carefully. The weights of grains from the plants of the ten sample hills were added to the respective plot yield to record the final grain yield of each plot. The grain yield was eventually converted to t ha-1.
Straw yield: Straw obtained from each unit plot including the straw of ten sample hills of respective unit plot was dried in the sun and weighed to record the straw yield of each plot and finally converted to t ha-1.
Lodging at maturity: Lodging score at maturity stage was measured by 1-9 scale as suggested by IRRI (1988) as follows :
1 = No plants were lodged
2 = Less than 20% plants were lodged
3 = 20-40% plants were lodged
5 = 41-60 plants were lodged
7 = 61-80% plants were lodged
9 = >80% plants were lodged.
Biological yield:
The biological yield was calculated with the following formula.
Biological yield = Grains yield + Straw yield.
Harvest index: Harvest index is the ratio of economic yield (i.e. grain yield) to biological yield and was calculated with the following formula (Gardner et al. 1985).
Harvest index (%) = 
x 100