RRS was calculated from percent cover in each floating weeds 45 days from the beginning of the experiment, according to the following formula of Dickinson and Miller (1998):
RRS = ((final cover - initial cover)/initial cover)/total # days ii) Weeds flora
During experiments weeds found in the experiment, field was recorded and determine the weeds flora is present in T. aman rice
iii) Weed population in weedy check plot (No.m-2)
From the pre-demarcated area of 1 m2 of weedy check plot, individual weed species name and their population were listed at 30 and 60 DAT for better understanding of the various weed interference of the experimented field.
iv) Relative weed density in weedy check plot
Relative weed density in the weedy check plot was estimated at 30 and 60 DAT. The relative weed density was worked out as per the formula given by Mishra (1968).
27
Relative weed density (%) =Number of individuals of same species
Number of individuals of all species × 100 v) Weed density (m-2)
From the pre-demarcated area of 1 m2 of each plot, the total weeds were uprooted and were counted at 30 and 60 DAS in the experimental field of rice.
vi) Weed dry matter weight (m-2)
After counting the fresh weeds, weeds were then oven-dried at 800C until a constant weight was obtained. The sample was then transferred into desiccators and allowed to cool down to room temperature and then the final weight of the sample was taken at 30 and 60 DAS of rice respectively.
vii) Weed control efficiency (WCE)
Weed control efficiency was measured by using the following formula given by Mani et al., (1973).
WCE =Weed population in control − weed population in treated plot Weed population in control
× 100
viii) Weed control index (WCI)
Weed control efficiency was measured by using the following formula given by Mishra and Tosh, (1979).
WCI =Weed dry weight in control − weed dry weight in treated plot Weed dry weight in control
× 100
ix) Plant height (cm)
The height of the randomly selected 10 plants was determined by measuring the distance from the soil surface to the tip of the leaf at 15 DAT intervals and harvest respectively. Mean plant height of rice plant were calculated and expressed in cm
28 x) Number of tillers hill-1
The number of tillers hill-1 were counted at 15 days interval up to harvest from pre-selected hills and finally averaged as their number hill-1. Only those tillers having three or more leaves were considered for counting.
xi) Leaf area index
Leaf area index was estimated manually by counting the total number of leaves per plant and measuring the length and average width of the leaf and multiplying by a factor of 0.75 (Kluen and Wolf, 1986). It was done at 30, 45, 60, and 90 DAT.
Leaf area index =Surface area of leaf sample (cm2) × Correction factor Ground area from where the leaves were collected xii) Dry matter accumulation plant-1(g)
Dry matter accumulation plant-1 (g) was recorded at 30, 45, 60, and 90 DAT.
The sample plants were oven-dried for 72 hours at 70°C and then data were recorded from plant samples plant-1 plot−1 selected at random from the outer rows of each plot leaving the borderline and expressed in gram.
xiii) Crop growth rate (CGR) (mg cm-2 day-1)
The average daily increment in plant stand is an important characteristic. The CGR is an increase in dry matter production per unit ground area per unit time.
In the present investigation, the crop growth rate was worked out between 60 to 90 DAT with the help of the following formula given by Watson (1956).
Crop growth rate (CGR) = 𝑊2−𝑊1
𝑃(𝑡2−𝑡1)mg cm-2 day-1 Where,
P = ground area (cm-2)
W1 = dry weight per unit area at t1
W2 = dry weight per unit area at t2
t1 = time of first sampling t2 = time of second sampling
29 xiv) Relative growth rate (mg g-1 day-1)
The relative growth rate expresses the increase in dry weight at time intervals concerning initial weight. In practical situations, the mean relative growth rate was calculated from measurements on dry weight at the time intervals (Between 60 to 90 DAT) with the help of the following equation suggested by Beadle (1985).
Relative growth rate = 𝐿𝑛(𝑊2)−Ln(𝑊1) (𝑡2−𝑡1)
Where,
Ln = natural log values
W1 = dry weight per unit area at t1
W2 = dry weight per unit area at t2
t1 = time of first sampling t2 = time of second sampling
xv) Net assimilation rate (NAR) (mg cm-2 day -1)
It is an increase in dry weight of plant per unit leaf area per unit time (Between 60 to 90 DAT). The net assimilation rate was calculated from the following equation given by Gregory (1926).
Net assimilation rate =(𝑊2−𝑊1)( LnLA2−LnLA1)
(𝑡2−𝑡1)( LnLA2−LnLA1) mg cm-2 day -1 Where,
LA1 = leaf area of the first sampling LA2 = leaf area of the second sampling W1 = dry weight per unit area at t1 W2 = dry weight per unit area at t2 t1 = time of first sampling
t2 = time of second sampling Ln = natural log values
30 xvi) Panicle length (cm)
Measurement of panicle length was taken from the basal node of the rachis to the apex of each panicle. Panicle length was measured with a meter scale from 10 selected panicles and the average value was recorded.
xvii) Number of effective tillers hill−1
The total number of effective tillers hill−1 was counted as the number of panicle bearing tillers per hill. Data on effective tiller per hill were recorded from 5 randomly selected hills at harvesting time and the average value was recorded.
xviii) Number of non-effective tillers hill−1
The total number of non-effective tillers hill−1 was counted as the tillers, which have no panicle on the head. Data on non-effective tiller hill-1 were counted from 5 pre-selected (used in effective tiller count) hills at harvesting time and the average value was recorded.
xix) Number of filled grains panicle−1
The total number of filled grains was collected randomly from selected 5 plants of a plot and then the average number of filled grains per panicle was recorded.
xx) Number of unfilled grains panicle−1
The total number of unfilled grains was collected randomly from selected 5 plants of a plot based on, no or partially developed grain in panicle and then the average number of unfilled grains per panicle was recorded.
xxi) Number of total grains panicle-1
The number of fertile grains panicle-1 alone with the number of sterile grains panicle-1 gave the total number of grains panicle-1.
xxii) Weight of 1000-grain (g)
One thousand cleaned dried seeds were counted randomly from each sample and weighed by using a digital electric balance at the stage the grain retained 12% moisture and the mean weight was expressed in gram.
31 xxiii) Grain yield (kg)
Grain yield was adjusted at 14% moisture. Grains obtained from each unit plot were sun-dried and weighed carefully. The dry weight of grains of the central 1m2 area was measured and then record the final grain yield of each plot-1 and finally converted to t ha-1 in both locations. The grain yield t ha−1was measured by the following formula:
Grain yield (t ha−1)= Grain yield per unti plot (kg) × 10000 Area of unit plot in square meter ×1000
xxiv) Straw yield (kg)
After separating the grains, the straw yield was determined from the central 1 m2 area of each plot. After threshing, the sub-samples were sun-dried to a constant weight and finally converted to t/ha-1. The straw yield t ha−1 was measured by the following formula:
Straw yield (t ha-1) = Straw yield per unti plot (kg) × 10000 Area of unit plot in square meter ×1000
xxv) Biological yield (t ha-1)
The summation of grain yield and above-ground straw yield was the biological yield. Biological yield =Grain yield + Stover yield.
xxvi) Harvest index (%)
The harvest index was calculated on a dry weight basis with the help of the following formula.
Harvest index (HI %) = Grain yield
Biological yield × 100 Here, Biological yield = Grain yield + straw yield 3.19 Economic analysis of rice cultivation
In this research from the beginning to end of the experiment, individuals cost data of all the heads of expenditure in each treatment were recorded carefully and classified according to Mian and Bhuiya (1977) as well as posted under different heads of cost of production.
32 i. Input cost
Input costs were divided into two parts. These were as follows: