Effects of Seed Carriers on Seedling Establishment after Fluid Drilling

Abstract

S U M M A R Y Six products possessing suitable physical properties as fluid carriers for pre-germinated seed were assessed for their effects on seedling emergence. Both glasshouse and field experiments measured the carriers' performance on eight crop species at varying extrusion rates and under different environmental conditions. Synthetic clay or polyacrylate increased seedling emergence by 10% compared with the sodium alginate control. Seedling emergence was least affected by moisture stress when synthetic clay was used as the carrier.Fluid drilling is a technique in which seeds, usually pre-germinated under ideal conditions, are suspended in a liquid carrier and then sown with a special drill (Currah, 1978). Considerable improvements in seedling establishment have been shown for a number of vegetable crops, as summarised by Salter (1978).The fluid carrier used in this early work, a form of sodium alginate which forms a thixotropic gel with good seed suspension properties, gave generally good results but had three main disadvantages, namely it was sensitive to the calcium hardness of the water used, which resulted in variable suspension characteristics; a high shear-force was required to mix the sodium alginate with the water; and (most important) under drying soil conditions the gel formed a tough film that trapped germinated seeds, giving poorer establishment than from conventional drilling. Furthermore, increasing the extrusion rate depressed seedling emergence (Gray, 1978). It was therefore apparent that carriers with improved properties were needed if the full potential of the technique was to be realised.The essential characteristics of a desirable carrier are that it should suspend seeds of various sizes for at least 24 hours, and yet be easily pumped through the delivery tubing. It should be non-phytotoxic, and easily mixed with waters of different pH, mineral content and hardness. It should not dry to form a skin but break down easily in the soil, with or without the use of a degrading agent, and be relatively inexpensive. It is also possible that a fluid carrier might provide an environment suitable for seedlings on the surface, without the seed being covered with soil.The physical and rheological characteristics of more than 40 materials were assessed by the Gels and Proteins Section of the British Food Manufacturing t Present address: Rothamsted Experimental Station, Harpenden, Herts, AL5 !>JQ, UK.

Effects of Seeding Treatment and Soil Moisture Content on the Emergence of Lettuce

“…Ross and Hegarty (1979) (Table 2) whereas percent FC had a significant affect among the dry seeded treatments. These results also suggest the possibility of the gel supplying some moisture to the developing seedling as reported by Elliott (1976 Gray (1978) and Darby (1980) Brocklehurst (1979) suggested that decreases in seeding emergence of fluid drilled treatments could result from limited oxygen availability to the seed, especially under wet soil conditions. Under the conditions of this experiment, the lower emergence levels could be related to reduced oxygen availability or at least related to some physical impediment imposed by the gel.…”

“…Sowing pregerminated lettuce seed using the fluid drilling tech-nique has alleviated problems associated with seedling emergence at low (FinchSavage 1981) and high (Gray 1977;Darby 1980) soil temperatures and has improved seedling emergence when soil moisture was limited (Gray 1978). Earlier and more uniform emergence with fluid drilling compared to dry seeding has resulted in increased weight and uniformity of lettuce heads at harvest (Hemphill 1982).…”

“…Although these factors have been investigated (Gray 1978;Darby 1980) At these levels, moisture is not necessarily a factor that will significantly reduce the emergence of dry seeded lettuce as seen in the cumulative emergence data in Table 2. Rather, seedling emergence will be delayed since more time is needed for dry seed to imbibe, germinate and emerge as illustrated by the data for initial, SOVo and cumulative emergence after 6 days.…”

The Tomato Crop

“…Elliot (1967) was the first to use the technique experimentally and suggested that the gel provided water to the developing seedling. Under very dry soil conditions, some gels may actually dry out and trap the seedlings (Darby, 1980). Under very dry soil conditions, some gels may actually dry out and trap the seedlings (Darby, 1980).…”

The effect of seed treatment and seed covering medium on the establishment of crisp lettuce

“…There were 12 seed and covering-medium treatments involving all combinations of three types of seeds: 'splitkote' pellets, natural and pre-germinated seeds from the same seed lot of the variety Pennlake, and four covering media: frame soil, 2-5% Laponite (a synthetic mineral clay gel used for fluid drilling (Darby, 1980)), Grade 3 vermiculite and a 50:50 (by volume) sedge peat-vermiculite mixture. The Laponite concentration (2-5%) was greater than that normally used for fluid drilling (1-5%) in order to retain gel structure when surface-sown.…”