1Research Agricultural Engineer, USDA - Agric. Research Service,

Smith Agric. Engineering WSU, Pullman, WA 99164-6120

We now know through more recent research and farming experiences that conservation tillage farming can in fact produce equal or better yields if proper machinery and methods are applied (Walker, 1983). But neither the machines nor methods for conservation tillage can be reliably extrapolated from those for conventional tillage. A new system of machines, chemicals, and methods must evolve.

Seed and fertilizer placement has continued to be one of the most troublesome operations causing risky and poor performance in conservation tillage, especially in cereal grain production (Lindwall and Anderson, 1977; Payton et al., 1985; Erbach et al., 1983; Wilkins et al., 1983; Babowicz et al., 1985). Most conservation tillage seeders have been adaptations of conventional machines and thus have not performed acceptably in many situations. For conservation tillage (especially n -tillage to succeed, biological risks of stand establishment and growth must be less than or no worse than those of conventional tillage.

It has been common to assume that designs of conservation-tillage tools should arise by extrapolation from tools designed for tilled seedbeds with only relatively minor modifications for robustness. This is likely not a good assumption. For example, because of the availability of high-humidity vapor-phase water in an untitled seedbed on which surface residue has been carefully managed (including micro-management during drilling), it is now clear that such a seedbed has more potential to germinate seeds and emerge seedlings than a tilled soil, especially when the soil is dry (Baker, 1976). The method of creating no-tillage drill slots has a major effect on the loss rate of soil water vapor (Choudhary and Baker 1981b). Compared to tilled seedbeds, residue covered soils often have different depth patterns of soil moisture, temperature, and densities in the seed zone, thus seeding depths and methods must also be different.

Slot shape and soil and residue cover of the seed furrow are the single most important biological variables in opener design (Baker, 1976). In this respect, most drill openers until recently have created essentially two shapes of soil slot with some minor variations within each. These are "V" and "U" shapes.

V-shaped slots are created by double or triple disc configurations. Their most advantageous features are an ability to physically handle surface residue without blockage and to incur low maintenance. These attributes are countered, however by: 1) an inability to optimize the seed-zone micro-environment, particularly water vapor retention and oxygen movement in both dry and wet soils (Choudhary and Baker, 1981a; Baker et al., 1987, 1988); 2) a tendency to smear and compact slot walls (Baker and Mai, 1982) which induces embryonic root-stress at the near-vertical slot-wall interfaces; 3) a tendency to tuck residue into the slot where it affects germination by releasing phenolic acids upon decomposition; 4) a wedging action in the soil which creates little loose covering material; and 5) a marked dependence on slow speeds to avoid "seed-flick" by the discs.

There is little opportunity for simultaneous but separate placement of fertilizer and seeds in V-shaped slots since the shape itself tends to concentrate them together at the base of the slot producing an undesirable interaction. Most designers have reluctantly utilized separate and additional fertilizer openers to avoid contact, but this has introduced additional demands on drill design and tractor power.

A wider range of openers than V-shaped slots creates u-shaped slots, so generalizations become more difficult. For example, various hoes, flat-angled discs, dished discs, and power-till openers all create various configurations of U-shaped slots. These openers produce seed-zone microenvironments somewhat more optimal than V-shaped slots but yet cause tillage, moisture loss, and randomized seed-soil contact. They all produce loose soil, which can be utilized later for slot cover, albeit that little micro-control is exercised over surface residue in the vicinity of the slot. The residues are indeed often swept aside as a prerequisite to avoiding opener blockage resulting in loss of moisture control, though this also avoids residue tucking.

Separated fertilizer placement in the vertical plane of U-shaped slots has been achieved with modifications to hoe configurations, although the success of this action is very dependent on soil-plasticity and machine speed and the soil below the seed is often quite fractured and of low density (Wilkins et al., 1983; Hyde et al., 1979). Disc and power-till openers have similar problems to V-shaped openers in this respect although there is less tendency to collect seed and fertilizer together at the base of the wider U-shaped slots

While U-shaped slots may experience soil smearing and compaction when made with either hoe or power-till options, this is usually not accompanied by side-wall or slot-base compaction, and dished disc and angled flat disc options are mostly free of smearing tendencies altogether. Similarly, because the slot wall interfaces of U-shaped slots include broader bases than V-shaped slots, root penetration is less restricted. Both U- and V-shaped slots benefit from pressing seeds into the base of the slot. This action partially eliminates the need for embryonic roots to negotiate any slot-wall interface and in this respect leaves them in a similar position to a tilled soil where slot interfaces are rare (Baker and Choudhar, 1988).

Hoe type openers have difficulty passing through heavy residue without blocking unless individual openers are spaced widely apart which creates undesirable spatial demands on drill designs. They are, however, usually constructed of components which are inexpensive and less stressed compared with angled discs (flat or dished) and power-till alternatives. As with V-shaped slots, the measure of economic viability depends on the value put on the risk of stand loss, although such a risk is generally lower with U-shaped slots than V-shaped slots (Baker and Desborough, 1984).

The cross-slot configuration was developed at Massey University, (Palmerston North, New Zealand) beginning in 1969 when researchers were attempting to create a slot shape which contrasted with V- or U-shapes for comparative purposes. Geometrical options were limited and eventually the wide-top-narrow-base features of V-shaped slots were reversed to produce a narrow-top-wide-base inverted T-shape. A shank with lateral wings could realistically create such a shape, although attempts were made to use paired dished discs for this purpose but their action was found to be too speed dependent.

Biologically, the cross-slot configuration has consistently produced significantly better seedling emergence results than either V- or U-shaped slots (Baker, 1979). This shape has especially increased the tolerance of seeds sown into soils that are sub-optimal (too dry or too wet). For example, fifty- percent emergence of wheat was achieved from the cross-slot in a soil at almost wilting point, which had no emergence with V- or U-shaped slots (Choudhary and Baker, 1982). In a residue-covered soil containing a good population of earthworms which was wetted with 420 mm rain over 21 days after drilling, the cross-slot opener produced 75 % emergence of barley while V- and U-shaped slots promoted only 17% and 65% emergence respectively (Baker et al., 1988).

The dry soil performance from the cross-slot has been shown to be a function of moisture retention within the slot (Choudhary and Baker, 1981b). It has been determined that this moisture retention is controlled by the diffusion-resistance of the soil and residue slot cover. The increased germination and emergence of the cross-slot configuration can be attributed to its capability to return residue-covered soil back over the slot from whence it came; i.e., seed-zone micro-management of soil and residue (Baker and Choudhary, 1988).

Wet soil performance has also been linked to residue retention over the slot while simultaneously avoiding tucking it into the seed zone. In this case the residue has greatly influenced mobility and numbers of earthworms which provided more oxygen diffusion and infiltration into the seed zone than other opener types (Baker et al., 1987 and 1988).

As a result of early repeatedly promising biological results, mechanical solutions to other problems with cross-slot openers were given high priority. Over a period of 10 years, engineering answers have been found to fertilizer placement (Baker and Afzal, 1986), residue handling and machine wear. These were combined to form the basis of an internationally patented opener design similar to that shown in Figure 1 as recently produced by the licensed firm of Agri systems Inc., Ltd. of Seattle, WA (Baker et al., 1979). These openers are mounted in two ranks; forward and rear drill frame tool bars, to provide row spacing options. Figure 2 illustrates the first U.S. prototype drill utilizing these openers.

The vertical shank of the simple original winged tool was split longitudinally. Each side of this dissected shank, with its horizontal wing, was positioned so the front edge rubbed on a central disc. The contact force and blade position was designed to be self- adjusting through soil pressure.

Seed is deposited on a soil shelf on one side of the coulter, while fertilizers deposited on the other side as shown. The fertilizer depth may be at or below the seed level. While the horizontal separation of seed and fertilizer is only about 20 mm., it is intersected by the vertical disc cut and is neither speed nor soil-plasticity dependent. Numerous field and laboratory studies have shown such separation to be effective from both crop stand and yield viewpoints (Baker and Afzal, 1986). Placing fertilizer with the same opener, which sows the seed greatly, simplifies the complete drill design.

While any slot created by a sliding rigid tool of this nature produces some smearing in wet soils, smears only appear to be noticeably restrictive to root penetration when they are permitted to dry and become in-groove crusts. Because of the self-closure and humidity-retention properties of the cross-slot, internal drying and crusting are minimized. In addition, slot-base compaction is largely avoided because the wings travel with a forward incline (lift) of 5 degrees to the horizontal, which is maintained with parallel drag arms between the drill frame and the openers.

The intimate contact maintained between the winged side blades and the disc ensures that heavy residue can be handled without blockage. With the aid of angled packer wheels, the residue-covered flaps of soil which are hinged up by the wings to allow deposition of seed and fertilizer are carefully folded back from whence they came to produce a residue covered soil surface over the seeded row. The cross-slot opener is not significantly speed-affected.

As with any slot shape, seed depth control is a function of both the depth-controlling wheels and skids and how the opener releases the seed underground. In this respect, the cross-slot opener design is capable of seeding with a high degree of accuracy. Depth control is with packer wheels positioned just rearward of the seed drop on each opener. Many designs have given low priority to this fundamental function of no-tillage openers which by definition will always be operating on fields which are at best unscathed by final tillage operations and at worst are deliberately roughened by primary tillage or weeding operations. Recent adapt ions in the U.S. have included self-contained mounting brackets and hydraulic cylinders for easy mounting and row spacing adjustments, air delivered seed and dry fertilizer to the openers and tubes on the side blades for liquid fertilizers and other chemicals.

The cross-slot opener design requires high performance manufacturing to maintain necessary tolerances and rigidity. It is thus a relatively expensive capital tool although the replacement soil engaging components are both inexpensive and easily changed. The economic viability of the tool will therefore be dependent on: 1) its higher biological reliability and tolerance compared with other technology and 2) its wide applicability over many types of soil and residue conditions for a variety of farming styles and needs.

Winter wheat yields were summarized from plots using two conservation tillage drills -- a large diameter leading-edge double disc type and a cross-slot type as shown in Figure 3. These were variously tilled fallow test plots in east central Washington State, USA. Eight large lots (30 by 120-m) were seeded in1987 with field scale drills (6 and 8 m widths). Both drills banded the fertilizer at seeding time parallel to the seed row--the double disc between pairs of rows and 10 cm deep and the cross-slot about 2 cm beside and either at the same depth or 2- to 5-cm below the seed depth for each row. In the pre-seeding fallow tillage, the chiseling was a very shallow surface roughening, the discing was a shallow surface pulverization, cultivation produced a very deep tillage and very rough surface, and the no-till was a quite smooth and firm surface. All plots had a very low rate of the previous crop residues (approx. 0.2-0.5 t/ha.

Both drills had difficulty maintaining depth control in the loose, chiseled ground, but the cross-slot was able to do much better because of its individual depth control packer-depth wheels. The early spring stand counts (3-5 leaf stage) shown in figure 4 for these same plots reflected the seeding depth and seedling survival capability from the two drills. Notable were that both drills had their best stands established where no previous tillage had been done (chemical fallow) during the preceding fallow year. The lower stand counts resulted in less yield not only due to the fewer plants but also because of increased weed population with less plant competition. These results demonstrated: 1) that the cross-slot opener performed better in a wide variety of soil surface tillage conditions, 2) better yields were achieved in this soil and climate with no tillage during the fallow period by using chemical weed control.

Wheat yields were also summarized from seven separate 1988 experiments at two locations in eastern Washington State, which had direct comparisons with the double-disc and the cross-slot type of openers. These mean values shown in Figure 5 were not weighted by size of experiment or samples taken. The results were for both spring and winter wheat varieties with and without fertilizer. Each drill was used on the same day in identical conditions on randomized plots in as precisely the same manner as possible with regard to fertilizer and seed rates for each experiment. In all experiments, the cross-slot opener produced higher yields than the double disc. An average of all seven experiments, which included 236 individual plot samples, showed that the cross-slot produced 4140 kg/ha, compared to 3585 kg/ha for the double-disc, a15.3 % increases.

Conservation-tillage, as a soil conservation practice of unparalleled merit, has progressed since its inception in the early 1960's to where even the skeptics no longer doubt that it is an effective conservation practice and can produce equal or improved yields compared to conventional tillage. Widespread adoption of the technique, particularly in cereal grain regions, has been severely restricted because of drill capability for stand establishment and simultaneous placement of fertilizers. The cross-slot drill opener has shown the potential to provide a higher level of mechanical capability and biological tolerance with reduced risk to the farmer for conservation-tillage seeding.

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