Harvesting systems can be grouped as coupled systems and uncoupled systems. Ideal coupled systems have a continuous flow of material from the field to the plant. An example is the wood harvest in the Southeast United States; wood is harvested year-round and delivered directly to the processing plant. Uncoupled systems have various storage features in the logistics system.

Sugarcane harvesting is an example of a coupled system for an herbaceous crop. (The sugarcane harvest season in South Florida is 140 days, not year-round as with wood throughout the Southeast.) The harvester cuts the cane into billets about 15-in long and conveys this material into a trailer traveling beside the harvester (Figure 13.5). The harvester has no on-board storage — a trailer has to be in place for it to continue to harvest. The trailer, when full, travels to a transfer point where it empties into a truck for highway hauling (Figure 13.6). Each operation is coupled to the operation upstream and downstream. If the truck is not there for the trailers to dump into, they cannot return to the harvester, and the harvester has to stop. It requires four tractors, trailers, and operators to keep one harvester

operating. The trucks have to cycle on a tight schedule to keep the trailers moving. One breakdown delays the whole operation.

A “silage system” can be used to harvest an herbaceous crop for bioenergy. With this system, a forage harvester chops the biomass into pieces about one inch in length and blows it into a wagon beside the harvester. This wagon delivers directly to a silo, if the field is close to the silo, or it dumps into a truck for a longer haul to the silo. All operations are coupled — a wagon must be in place to keep the harvester moving, and a truck must be in place at the edge of the field to keep the wagons cycling back to the chopper. It is a challenge to keep all these operations coordinated.

A coupled system can work very efficiently when an industry is integrated like the sugarcane industry in South Florida. There, the sugar mill owns the production fields surrounding the mill and the roads through these fields. The mill controls everything: har­vesting, hauling, and processing. Because sugarcane has to be processed within 24 hours after harvest, the need for an integrated industry is obvious.

An example of an uncoupled system is the cotton industry using the new cotton harvester that bales cotton into 7.5-ft diameter by 8-ft long round bales of seed cotton (Figure 13.7). This system was developed to solve a limitation of the current module system. With the module system, in-field hauling trailers, given the rather quaint name “boll buggies”, have to cycle continuously between the harvester and the module builder at the edge of the field. The best organized system can typically keep the harvester on the row harvesting cotton only about 70% of the total field time. Harvesting time is lost when the harvester has to wait for a boll buggy to get into position beside the harvester so the bin on the harvester can be dumped.

The round bale cotton harvester is designed to form a bale, wrap it in plastic, and eject it without stopping the harvester. A new bale is begun while the current bale is being wrapped and ejected. (Current round balers for hay have to stop, wrap the current bale, and eject it before beginning the next bale.) The round bale cotton harvester, because it is uncoupled from the in-field hauling operation, can achieve a 90% field efficiency. This means the harvester is actually harvesting cotton for 90% of the in-field time compared to 70% for the

current harvester in the module system. Repeating a principle stated earlier, more tons/hour through the harvester means the $/ton harvest cost is less.

Techniques have been implemented to improve the in-fleld hauling of round bales of seed cotton. As shown in Figure 13.8, the harvester can carry a completed bale and drop it at the edge of the field to facilitate direct loading onto highway hauling trucks.