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Important Index for the Use of Biological Purpose

The most important index of biological advantage is the relative yield total (RYT) introduced by De wit or Land van Den Bergh (1965) or land equivalent ratio received by Willey (1979).

1. The mixture yield of a component crop expressed as a portion of its yields as a sole crop from the same replacement series is the relative yields of the crop and sum of relative yields of component crop is called Relative yield total ( RYT).

2. The total land area required under sole cropping to give the same yields obtained in the intercropping is called Land equivalent ratio (LER).
Both the expressions (RYT and LER) are similar.

1. Land Equivalent Ratio (LER):

This is the most frequently used efficiently indicator. LER can be defined as the relative and sole crop that would be required to produce the equivalent yield achieved by intercropping.
LER = Yab + Yba
____    ____
Yaa       Ybb

Where, Yab = yield of crop an in intercropping, Yba = yield of crop b in intercropping, Yaa = yield of crop an in pure stand and Ybb = yield of crop b in pure stand.

LER of more than 1 indicates yield advantage, equal to 1 indicates no grain or no gain or no loss and less than 1 indicates yield loss. It can be used both for replacement and additives series of intercropping.
LER is the summation of rations of yields of intercrop to the yield of sole crop.
Example: Let the yields of groundnut and red gram grown, as pure crops are 1,200 and 1,000 kg/ha, respectively. Let to yields of these cops when grown, as intercrop be 1,000 and 600 kg/ha, respectively. The land equivalent ratio of groundnut + red gram intercropping system is

LER of groundnut =   Yield of intercrop    =   1000
_______________       _______
Yield of sole crop         1200
LER of red gram    = 600
____
1000
LER of system = 1000 + 600
_____ _____ = 1.43
1,200 1000
LER of 143 indicates that a 43 percent yields advantage is obtained when grown as intercrop compared to growing as sole crops. In other words the sole crops have to be grown in 1.43 ha to get the same yields level that is obtained from 1.00ha off intercropping.

2. Relative Yields Total (RYT):

The mixture yields of a component crop expressed as a portion of its yields as a sole crop from the same replacement series is the relative yield of crop and sum of the relative yields of component crop is called Relative Yields total (RYT). Or When LER is compared at uniform overall plant density of sole and intercrops then it is known as RYT. In RYT yields advantages is to measure not only unit area, but also on unit population. This is mainly used for replacement series.

LER = Yab + Yba
____   ____
Yaa    Ybb
Where Yaa = yields of component a as sole crop Ybb = yields of component b is a sole crop
Yab = yields of component a as intercrop in b Yba = Yield of component b as intercrop in a.   Example: in pasture mixture, Stylo and anjan grown in 1:1 ratio with 50% sole crop population of both crops. In I/C, mixture yield (50%) for Stylo and anjan is 6 and 4 tons/ha of fodder, respectively. The yield of these crops in sole stand with 100% PP is 10 and 8 ha of green fodder, respectively.
RYT = 12+8/10+8 = 20/18 = 1.11.
So RYT 1.11 indicates 11% extra fodder yields obtained by mixture.
Two crops yields in the intercrop mixture are MA and MB and the yield of crops grown of crop are SA and SB then the combined index is

L = MA+ MB = LA +LB
___     ___
MB     SB
The intercrop embodied in LER is that L represents the land required for sole crops to duce yields achieved in the intercropping mixture. A value of L greater than (1) indicates overall biological advantages of intercropping. The two component of total index LA and represent the efficiency of yields production of each crop when grow in mixture, relative to crop performance.
Lative crowding Coefficient: the other index used in relative crowding coefficient which can define in terms of LER component as

LA *     LB
___        ____
1 – LA    1- LB
The two main indices of dominance are the aggressively and competition index. Aggressively gives a simple measure of how much the relative yield increase in species. A is after than that species B. It is an index of dominanance
Aggressively = Mixture yields of A    – Mixture yields of B
_________________    ________________
Expected yields of A     Expected yields of B

= sown portion of species A and B are represented of ZA and ZB, respectively. An aggressively value Zero indicates that the component species are equally impective. A positive sign indicates the dominant species and a negative sign the dominated.

The basic process in the competition index is the calculation of two equivalence factors, one each component species. It is the product of two equivalence factors, one for each component species.
Effective Land Equivalent Ratio (ELER): Mead and Willey (1980) showed that any required ratio could be achieved by growing the intercrop of the land area and one of sole crops the remainder.
P = (La + E)
__________
(LER + E)

LER is a measure of the nat advantages from the combined intercrop determined by adding the crop and sole crop relative yields.
ELER =    Lb
____________________
(( 1- La) + ( LER – 1) P)

Staple Land Equivalent Ratio: in situation where the primary objectives is to produce yields of one component (staple crop) usually a cereal and some yields of the legume.

3. Land Equivalent Coefficient (LEC):

It was proposed by Adetilaye and Ezedinma ( 1986) the product of ler of intercrop components.

= MA * MB
_________
SA * SB

It can therefore, be regarded as a measure as a measure of association or interaction when crop with the strength of relationship for a two crop mixture the minimum expected product by yield advantage is obtained and LEC greater than 0.25 (25%). This was obtained from the 50:50 yields where interspecific competition equaled intraspecific competition.

LEC = la * LB = 0.5 * 0.5 = 0.25.

The LEC is developed to assess the interaction and potential of crop mixture. It is derived from the understanding that the in intercrop yields, as compare optimum sole crop yield is due competition assuming that the inter competition is absent.

4. Area Harvest Equivalency Ratio (AHER):

This was proposed by BAL Subramanian and sekayange (1990). It indicates resources efficiency.
The concept of AHER combines the area time factors in a practical sent quantifying intercrop yield advantage particularly in multiseason.