Assuming your farm income and expenses are taxed according to the rules for farm income, the amount you spent on the pump would be capitalized and deducted accordingly, just like any other capital asset. Yes, in other words.
Property that qualified for the special credits would have been labeled in store, as these things are rated and pre-qualified before they hit the shelves. Here are IRS links to the energy efficient property credits that were recently enacted, though they were more geared for non-business property:
"Residential Energy Efficient Property Credit (Section 1122): This nonrefundable energy tax credit will help individual taxpayers pay for qualified residential alternative energy equipment, such as solar hot water heaters, geothermal heat pumps and wind turbines. The new law removes some of the previously imposed maximum amounts and allows for a credit equal to 30 percent of the cost of qualified property. See Notice 2009-41. "
"(a) Qualified solar electric property expenditures are expenditures for property
which uses solar energy to generate electricity for use in a qualifying dwelling unit." - Notice 2009-41
(2) Qualifying Dwelling Unit.
(a) Except as provided in section 3.01(2)(b) of this notice, a qualifying dwelling
unit is a dwelling unit that is located in the United States and is used as a residence by the taxpayer. - Notice 2009-41
A farm and a residence are not one and the same, so be careful here.