I place my t-tapes next to the plants. So if you have 4 rows 12" apart I would use one section of t-tape per row.

how far apart should the t-tape be for a 36" row with beans or peas in it? down the center at 18"?

also I have 36" path between all of my rows

Please keep in mind that water fans out as it goes downward. You may be using a soaker hose, t-tape, drip emitters or what have you and it may only wet a 3" wide strip on the surface (this depends on the soil type). Below the surface though capillary action pulls the water wider as it goes deeper.

For starting seeds you really want the seed bed kept moist (plant near the irrigation line), but for established plants with deeper, more spread out roots you do not have to get the surface of the entire garden wet, in fact you shouldn't to keep weeds under control.

Figure that virtually any plant in reasonably soft soil will put roots down to at least 4 inches. Run your tape a while and then turn it off and wait a couple hours. Then go dig down 4 inches and see how far the water has spread.

You want all of your plants to be able to put roots into that moistened area. This will govern how far apart you space your irrigation lines for the crop.

Some plants in reasonably soft soil will work roots out a few feet from their location, others just a few inches.

To start with figure that plants which are small also have small root systems and plants which are large have large root systems. By planting similar sized plants together you can use the same spacing for the runs.

With tomatos, for example, you might space them 3' apart in a row and then just run one tape along their path, but for small plants like lettuce or radish you might wish to run tapes closer together.

You will have to do a little trial and error, but will get it down in no time.

Excellent points Justaguy:

T-tape is rated by the flow rate in gallons/minute/1000 ft. Also keep in mind the emitter spacing, the closest I know of is 12" the most 36". Sad but true, you can waste ALOT of water with a mismanaged and improperly designed drip system (don't forget the filter and pressure regulator).

Soil texture (clay, loam, sandy, etc.) has a huge impact on how water moves away from the drip emitters both downward and laterally. In heavier soils, use lower flow rated tape and use longer irrigation cycles. this gives the water time to move laterally. Also keep in mind when irrigating through the year that each cycle sets up a front of dissolved salts (minerals) that get deposited at the furthest point of wetting. This is very important on some very salt sensitive crops like beans. Placing the tape very close to the bean row will avoid this problem. My bean rows are 1.5-2' apart and that works well if the wetting pattern extends beyond the plant rows by about 6" or so. For me it is extremely important with beans because my water is extremely hard (lots of salts). You really need to experiment with your soil/water/crop curcumstances.

One source for drip stuff is Hooks Point Irrigation 1-800-438-2452. i think I got my 500' roll for $48 and the parts that connect the tape to the header (w/valves) for $2 each.

Well, gotta go, good lusk!