This is one of my undergraduate assignment under department of Agronomy, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh.



Abstract





Wheat is the most important cereal crop of the world. Wheat grows well in different region in Bangladesh. Wheat cultivation is greatly affected by sowing depth. Sowing depth significantly influenced the seedling emergence and vigor index. Sowing seed deeper than 4 cm delayed & reduced seedling emergence & seed production. Seed placed at 8 cm depth resulted a greater degree (82%) of failure in emergence. Sowing at variable depths causes appreciable differences in grain yield. Sowing deeper than 4 cm greatly reduced grain yield. Plant emerged from 4 cm depth had produced the highest grain yield which was attributed to greater number of spikes per unit area and seeds per spikes. Deeper sowing caused in the number of seminal root but the total root length was significantly reduced. Deep sowing causes unnecessary elongation of stem between the seed and secondary roots. As a result the food reserves of the grain are taxed severely and seedling may even fail to emerge. When sowing at 4 inches reduced emergences by almost 40%.





Key Word: wheat (Triticum aestivum L.), yield, root, water, seedling growth.



Introduction





Wheat (Triticum aestivum L.) is the second most important cereal crop of Bangladesh. It was cultivated in about 1.93 million acres in 1995-96 and the total yield was about 1.57 million tones (MOA, 1997).In the beginning of wheat cultivation in Bangladesh in early seventies, the yield increases was rather dramatic (Swaminathan, 1987; CIMMYT, 1982), but for mid eighties the area under wheat and production seem to have remained static or registered a slight decreasing trend (Ahmed et al., 1987). Majority of wheat area is rain fed (Guler, 1987) and seedbed preparation for sowing seeds is often constrained by lack of soil moisture. During land preparation and immediately after seed sowing moisture of the top soil runs out quickly and the seeds particularly those placed at shallower depths are at risk of germination. The risk can be avoided by deep sowing. On the other hand, deep sowing is often reported to have adverse effects on crop establishment as well as yield.

In the light of the above discussion, the present study has been designed to examine the performance of wheat with the following objectives:



- To find out the effect of depth of sowing on the stand establishment, root systems development and yield of wheat.

- To the influence of sowing depth on the performance of wheat.

- To find out the depth of sowing depth that give higher yield.





Review of Literature





Wheat is a non traditional crop and its popularity as commodity in Bangladesh is very recent. The spectacular growths in wheat production a ten fold increasing during 1981-83 period (CYMMIT, 1982), relied on the package of production technology mainly imported from outside.(Saunderas,1988).During the recent year however it has evident that crop improvement technology is insufficient to increase national wheat yield or even to sustain advance previously made superior germplasm. Although systematic research on wheat improvement started in mid 60s, works on agronomic practices in what seems to be too inadequate (Saunderas, 1988).a part from research from varietals improvement. A few studies have carried on agronomic aspect of wheat production which mainly focus on the seed rate, sowing time, cropping system(Saunderas,1988;Annonymous,1990).but work relating to seed size or sowing depth effect on yield performance are either lacking or highly inadequate.



In this chapter we review some of the available reports. In absence of pertinent reports based on work done in Bangladesh the relevant research findings from other countries have been reviewed.



An extensive survey conducted in wheat grown area in Tangail showed that in the seed bed most seeds are placed beyond 8 cm plough zone (Matsunaga et al., 1989).generally the seeds are broadcast and incorporated in the soil working with ploughing and cross ploughing and resulting an uneven distribution of seeds into the plough zone. In most cases it is found that the upper layer of the soil dries quickly after land preparation. In that situation during sowing the seeds which fall on the shallower depth are at risk of germination due to less imbibition and seed soil contact. On the other hand the seeds which fall below the optimum depth fall to emerge. If the seeds are placed deeper than the length of coleoptiles the shoot have to push or displaced the superficial mechanical obstacles. (Boouaziz et al., 1990).



However in wheat work relating only sowing depth and plant performance in wheat has been reported recently (Saunderas, 1988).in the study 200 seeds are sown in macro plots at variable depth 2,4,6 and 8 cm. depth of sowing affected germination and emergence indicating that sowing at 8 cm was clearly detrimental.



Inadequate stand and even failure in stand establishment may result due to excessive mechanical impedance by dry surface seals (Arndt, 1965), or in absence of surface seal due to unfavorable soil moisture, since the soil water supply improves with depth, advantage should be gained by deep planting but since mechanical impedance also increase with depth (Arndt,1965;Hamid & Mohiuddin, 1992).



Short coleoptile is primarily responsible for poor seedling emergence under dry land farming (Singh et al., 1985).



Spikes per plant, spikelets per spike and kernels per spike at higher at sub optimal seeding densities (Darwinkel, 1978 and 1980; Wiley & Holiday, 1971) and this sub optimal density depend mainly upon seeding depth and seed bed condition.



Sowing depth contribute greatly to the crops stand establishment. Farmers seeding rate often exceed recommended dose but optimum population rarely occurred.

Tillage level, soil aggregate, size distribution in the seed bed, seedling vigor, seed health and planting depth are the major determinants of seed emergence and stand establishment (Mccloy, 1980)



Turner et al.(1982) observe that the cultivar differed in the potential of their coleoptile and mesopityle to elongate.



The root length & root diameter at different growth stages determine the water and nutrient uptake capacity of the plant. The seminal roots that grow in the early stage of the wheat, their functions being concerned with absorption of water and nutrient for the growth of the young plant appear to be functional throughout life of plant. The extent of their development and depth to which they descend is influenced by the texture of the soil and depth at which the seeds are sown (Percival,1985).



Hoque et al., (1992) examined the influence of sowing depth under varied seed bed condition, soil aggregate size and distribution greatly influence emergence and stand establishment of cereal crops.

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