Leguminous Vegetable Cultivation and Seed Production S ...

37 0 GREEN MANURE IN RICE FARMING
Table 4, Equilibrium moisture content of soybean at 25 0 C at 30-95% relative
humidity (RH) (Roberts and Roberts 1972).
Equilibrium moisture content at given RH
1 0% 30% 45%
60% 75%
95%
4.3 6,5 7.4 9.3 1 3.1 18.8
moisture content, it can be stored for 3 yr. At 20-30 °C, seed with 13-18% moisture
content will remain viable for less than a year (Toole and Toole 1946). Under
tropical conditions, high initial quality soybean seeds at 9-9.5% moisture content can
be safely stored 9 mo at 20-25 °C and 50-60% RH (Gregg 1982). Most AVRDC
breeding materials with good initial seed quality and 9-10% moisture content are
stored at 20-24 °C and 55-60% RH. The majority of the entries stored under these
conditions retained more than 80% viability for at least 2 yr. Similar storage
conditions are suitable for mungbean.
If storage conditions have a higher RH, there is no need to dry the seed to less
than equilibrium moisture content. At 45% RH or lower, seed should be dried to
7.4% moisture content or lower. At 60% RH, drying the seed to 9% moisture will
suffice. Soybean seed moisture content at 25 °C with different relative humidity
levels are given in Table 4.
The usual rule of thumb for storage conditions for the short term is percent RH
and degrees Fahrenheit totaling 100 or less (James 1961).
The viability of soybean is determined using an age index concept.
Age index (AI) = months in storage X Io'""( X 10
0.06451
Where MC = moisture content (%), T = temperature (°C), and months in storage =
Log AI-0.143M C-0.0645T.
Fungi activity during storage below 75% RH is very low; below 62% RH, all
storage fungi are completely inactive (Roberts 1972a). Below 60% RH, storage
insects are inactive. Because rnungbean weevil is a serious storage pest, it is
.important to maintain RH below 60% and seed moisture content below 8% (Roberts
1972a).
The minimum germination required for seed certification varies among
countries. For soybean, it is 80% in the US, but many seedmen demand 90%
(Tekrony et al 1978). In India, it is 70%. For mungbean, minimum germination in
India is 75% (Agrawal 1980).
Under ambient conditions, mungbean appears to be storable longer than
soybean (Table 5). Traditional mungbean varieties appear to have a high proportion
of hard seeds, but hard seededness decrease with age in storage. Mungbean seed
loses hard seededness with a year (Pathwardhan 1927).
During domestication, the hard seededness character was selected out. It
appears probable that this trait in mungbean can be used in breeding for good seed
quality (B. C. Irnrie, pers. comm.). Soon after harvest, hard-seeded rnungbean
germination is low, but it improves with storage (Rajasekara Mudaliar and