Modern farm equipment depends on clean fuel, correct oils, grease and coolants for dependable operation. There are many opportunities for contamination from dirt, water, farm chemicals and accidental misapplication of products or even malicious damage. This can result in expense repairs and downtime.
Farm Fuel Tanks
There are a number of problems associated with maintaining bulk fuel tanks. Water can condense in any fuel tank but especially in a humid climate or damp area. It is better to keep a tank as full as possible as that reduces the volume of air and moisture and the tank surface area which reduces condensation. Underground tanks in particular will require routine water removal. Overhead tanks may still have inaccessible pockets of water (e,g a "deep end" if the tank has subsided a little). Tank breather filters are recommended.
Biological growth or "diesel bug" is often blamed for fuel problems. If a water layer forms in a tank, given the right temperature conditions there are millions of biological organisms that can grow in that water. Typically it is anything airborne that enters the tanks and finds favorable conditions. This is essentially the same problem for any body of stagnant water - Algae, Bacteria, Fungi, Mold, Yeast etc. These growths tend to occupy the water layer and they can block filters. A blocked filter is a nuisance but it is the water itself that tends to pass through the fuel filter and does the real damage. Diesel bug can be an indication of a water problem. There are many commercial fuel treatment additives that contain a microbiocide to kill biological growth. Remove the water layer first to avoid a toxic water layer that is a heath and environmental hazard.
Diesel fuel is sold in Summer and Winter grades. In cold parts of the country it is wise to avoid purchasing Summer Diesel if it is likely to be carried over into winter (buy bulk fuel in winter instead). The heavier hydrocarbon molecules have a higher freezing point and these contribute to the Cloud Point of diesel fuel. If Summer diesel is used in sub zero conditions parts of it will turn to wax and block filters. Water also turns to ice and contributes to the problem. Wax will melt, so there is nothing wrong with the fuel or filters - just the temperature. Fuel suppliers can advise on cloud point and timing of seasonal changes for your area. Best solution is to avoid summer diesel in winter - additives and solvents won't achieve much more than the fuel supplier has already achieved with additives. Winter diesel has the heavier hydrocarbons removed in the first place - it has a lower energy content but it won't freeze up.
Modern farm machinery typically requires high specification modern lubricants and fluids and the days of multipurpose lubricants are basically over. Sometimes temporary labor can have complications with the right fluids being used in the right compartments or the odd case of malicious damage. Routine oil sampling is a good way to ensure that correct fluids are being used and that there is no contamination or abuse of equipment. The equipment lifetime and availability can be increased by monitoring fluids.