Production of Forage Legume Seed in Nepal
Feed shortages and the poor quality of available feed are the major constraints to increased livestock productivity in Nepal. Sowing a new pasture or improving an existing natural pasture requires a reliable source of seed or vegetative material of species recommended and adapted for the area. The objective of a forage seed program is to make available quality seed or vegetative material that is suited to farmers’ needs for livestock production. Farmers’ needs are variable depending on the environment, type and class of grazing animal and the animal product required. These needs may also include forage use for conservation (hay or silage), site stabilization (erosion) and amenity uses (turf). It is therefore necessary to ensure positive consumer reaction to new materials and accompanying production techniques to help farmer adoption of these materials. Here we the discussed about seed production systems, site selection, the plant and its growth forms, crop establishment, crop management and harvesting.
Seed production systems
In Nepal, no single system of seed production is suited to the varying social or environmental situations. Much of the forage seed production is in the informal or traditional seed sector where farmers do their own selection and seed production to meet their own needs and may also sell or exchange excess seeds within the local community.
Seed production systems involves following steps for the production of forage seeds. They are as follows:
Selection of site
An important requirement in seed production is for the grower to plant in areas or sites which are most likely to support high seed yields. Experience has shown that shoot density, the number of seeds formed per flower and the percentage harvest recovery of the seed are three of the most important factors contributing to seed yield.
Factors influencing site selection
Although soils are important, the location of the site for seed crops depends primarily on the climate. The weather, unlike nutrient and soil supply, may only be marginally modified by the grower. Seed production is generally encouraged by sunny weather. Areas with abundant radiation especially in the later stages of crop development are expected to have high seed production by encouraging rapid growth rates, flower opening and increased bee activity.
Temperature affects vegetative growth, floral induction, inflorescence growth and differentiation, flower opening, pollen germination and subsequent seed set and maturation. The effect may vary within and between species. It is difficult to give a generalized temperature range for seed growth and flowering. However, optimum temperature and temperature response for growth is different for each phase and varies between and within species. For example, the maximum growth and yield of Berseem occurs between 40-42°C, but maximum seed production occurs at 27°C.
b. Day length
Day length is the main environmental factor controlling flowering in many plants. It provides the measure of seasonal change and promotes flowering in many species. Day length sensitivity enables flowering to be initiated before adverse conditions occur and facilitates out crossing by synchronizing flowering.
There are three basic categories of day length response.
- Short-day: flowering stimulated by day length shorter than the critical length. Example: Cowpea, field bean, cluster bean.
- Long-day: flowering stimulated by day length longer than the critical length.
Example: Lucerne, red clover, white clover.
The soil requirements of forage crops vary significantly. Some crops prefer deep soil with a good moisture-holding capacity while others, such as the non-competitive legumes, can grow well on less fertile sandy soils. In general, a soil with good moisture-holding capacity is an advantage, especially with grasses, against unreliable rainfall and inefficient irrigation. Fertile soils of suitable pH are preferred.
Choice of varieties
High yielding varieties should be cultivated. The improved varieties of berseem are: Berseem Green Gold, Meskavi.
Sowing time and seed rate
Sowing time varies according to forage types. The optimum sowing time of berseem is October- November while the optimum sowing time of clover is March.
The main types of seedling methods are:
- Grain drill with grass seed attachment
- Corrugated roller
- No till
The proper placement of seed at right depth (2-3 cm) is very important for getting a good initial stand of crop. Most machinery will place the seed and roll the soil, but in broadcast seedling the seed is distributed and rolling must be additional step. Rolling can be done by machine or by dragging something heavy object over seeded area or allowing livestock to trample the seed into the ground. Requisite seed rate and appropriate spacing are the two important determinants of optimum plant population under field conditions.Optimum spacing plant to plant and row to should be maintained.
For example: A row to row spacing of 50cm in sorghum, cowpea, and lucerne; 25cm in berseem crops have been recommended for higher seed production. The seed rate of 25 kg/ha in cowpea, 5 kg/ha in white clover have been found optimum.
Seed treatment (Rhizobium/ fungicides):
Seed treatment with effective strains of rhizobia has benefited almost all the forage legumes. The usual rate of its application is 1 packet/10 kg seed. Majority of the seed borne diseases can be controlled effectively with little investment on fungicides.
Fertilizer and Manure application:
Main effect of nitrogeneous fertilizer on tropical and subtropical grass seed crops is to increase seed yield via inflorescence density. Lower rates of N are required in the establishment than for subsequent crops. Optimum nitrogen requirement varies depending upon the species, environment and the season. Seed yield responses to phosphorus have also been reported but are typically much smaller than responses to nitrogen and are not recorded where soil phosphorus levels are adequate. Soil tests will give information on the status of other nutrients (mainly P and K). If required, these should be applied annually based on general pasture recommendation. Application of plant nutrients as foliar spray is a low cost input, for increasing seed yield of forage crops many fold. To improve the fertility and seed formation, foliar application of nutrients has been recommended in forage crops.
Irrigation and Weed management:
Irrigate immediately after sowing. Irrigate at intervals of 7 to 10 days depending upon soil and climatic conditions. Flowering and pod formation stages are critical periods when irrigation is a must. Avoid water stagnation at all stages.
The importance of managing weeds in legume forage is critical for obtaining optimum yield. All grain legumes are relatively poor competitors with weeds and thus are prone to yield reductions when grown in the presence of weeds. A combination of practices, such as cultivar selection, planting date, tillage system, in-crop tillage or cultivation, and/or herbicides is needed to increase the likelihood of successful weed control.
To overcome the problems of genetic limitation causing poor seed yield, cutting management plays a significant role since it strikes a balance between vegetative and reproductive phases. With this practice, the age of growth and sprouting of plants can be suitably managed to synchronize the reproductive phase with the favorable photoperiod and temperature conditions. For berseem crop best time for last fodder cut was found to be first week of March. In lucerne crop, maintaining cutting height of 10 cm appeared to be physiologically active because of efficient sugar synthesis in leaf with active photosynthetic system dictating the development of potential flower with higher sugar content for seed formation. Similarly, the results revealed superiority of 10cm cutting height in berseem before leaving it for seed production due to higher gradient of sugar concentration and transport to active site.
Proper techniques should be adopted to control insect, pest and diseases. Manual hand picking, shaking should be done. Similarly yellow sticky trap should be placed at field. If severe condition dichlorovus (1-2ml/l of water), dimethoate (1-2ml/l of water) should be applied.
The harvesting of annual fodder crops does not pose any serious problem. However, seed collection of pasture legumes is more difficult than that of annual cultivated fodder crops. Therefore, flowering habit, seed maturation, appropriate harvesting methods and cleaning techniques need to be carefully observed to obtain high output in each growing season. In Nepal, forage legume seeds are generally collected by manual shaking, plucking, ground sweeping, cutting of inflorescence and cutting and threshing, based upon crop and season. In a study, a delay in harvesting after 10 days of peak flowering resulted in significant reduction in quantity and quality of grass seeds. Here, low seed yield could be attributed to loss of seeds through shattering. Hence, legume seeds need to be collected at right time to recover highest yield of viable seeds.
Agro-techniques constitute an important consideration for improving seed productivity in forage legume crops. Hence, selection of site, choice of varieties, proper cutting management and foliar nutrition etc. enhance seed productivity in forage crops. In nutshell, all these agro-techniques should be stressed upon in developing the improved technologies aiming at increasing seed productivity in forage legume crops.