Fixed-wing aircraft use venturi spreaders to distribute seed while helicopters use rotary-spinner spreaders. Venturi spreaders clamp to the gate box at the base of the hopper. The gate boxes are 25-, 38-, or 41-inches wide depending on the size of the aircraft. As the adjustable door (gate) on the gate box opens, seed from the hopper falls into the venturi spreader and airflow through the spreader distributes the seed. The amount the door is opened determines the seed flow rate. In some cases, the flow of difficult-to-meter seed can be improved by an agitator installed above the gate box. Hard, slick seed can be accurately metered with a positive metering system installed on the gate box. The system uses a rotating, fluted rotor to positively meter seed or pelleted material. Rotor speed is controlled by the pilot, and the system can be calibrated while the plane is on the ground. Rotary spreaders are self-contained units that hang below the helicopter and spread seed with a hydraulic- or electric-powered spinner. Additional information is covered in Chemical Control.
Seeding is the metering and distribution of seed either by broadcasting on the soil surface or by drilling seed in the soil at a predetermined depth. Special planters are required to place plants or plant parts in the soil. Direct seeding is generally preferred for revegetation projects because seed is relatively inexpensive, easily stored and transported, and some seed may be readily available or can be collected. Accurate metering systems distribute seed uniformly and increase the probability of success over the entire seeded area. Drill seeding places the seed in the soil at targeted depths and covers the seed, thereby increasing the probability of seedling germination and emergence. Broadcast seeding generally requires as much as 50% more seed to equal the results of drill seeding and seed should be pressed into the soil surface to improve seed-to-soil contact. Seedbed condition, quality of seed, probability of rainfall, and weed competition influence the chances of successful plant establishment.
Metering Systems. Seed metering and placement are key components of a drill/seeder. Hard, slick seed is easily metered in fluted or cup-feed mechanisms. Uniform metering of chaffy or fluffy seed plagued the industry for years. The development of the semicircular seedbox, auger agitator, and pickerwheel mechanism by the Texas Agricultural Experiment Station eliminated much of the metering variability, and it is now the industry standard. Slick and chaffy seed will not meter uniformly in a mix, therefore, separate seedboxes are required to meter these two seed types. Additional seedboxes are available to apply fertilizer, pesticides, or other slick seed.
Seed Placement. Placing seed in a seed furrow at a shallow depth and pressing the soil around the seed is often a challenge under rangeland conditions. The problem becomes complex when seed of some species needs to be placed at shallow depths while other species in the same mix germinate best when placed on the soil surface. Understanding these requirements determines the type of devices used. When clean-tilled land is present, double disk openers with depth bands and presswheels can be used very effectively. When brush debris, crop residue, or rocks are present, different approaches must be taken. These may include coulters to cut trash, modified disk openers, cultipackers, steel runner openers, chain harrows, chain drags, rubber-tire packers, or broadcast (no openers). When two rows of cultipackers are used, seed is dropped between the first and second row. Large diameter seed tubes (2 inches or more) are necessary to prevent clogging when dispensing chaffy seed.
Global Positioning System (GPS) is a technology that can locate positions or navigate the user to a location. GPS uses a constellation of 24 navigational satellites to determine positions on the earth's surface. Geographic Information System (GIS) is mapping software that can link information about where things are with information about the location, e.g. soil type, vegetation, topography, roads, etc. Combining GPS and GIS can direct tractors, four wheelers, aircraft, or persons on foot to desired field locations. Additionally, these systems can be programmed to direct mechanical operations, e.g. variable-rate sprayers, fertilizers, or seeders, etc. This technology is revolutionizing many agricultural operations.
Transplanting, Site Protection, and Fertlizing/Mulching
Descriptions of equipment and techniques for transplanting, site protection, and fertilizing and mulching are in process.