Too much soda is as bad as too little. You NEVER want pour it on the ground. Too much soda can crystallize in heat and reduce traction or get gummy can cause a greasy feeling track. As mentioned before garden sprayers are the best tools to spray a track.
Also, as edseb said blowing off the track must be done to get good results. Every track in Florida has a leaf blower ands a garden sprayer to prep the track. Considering what we spend on this hobby these two items are not too expensive for a shop, track, club to buy.
There are a lot of different compositions of asphalt that we race on but you can lump them together into 3 different stages of life.
1. New Asphalt: Black and soft freshly laid asphalt is the highest traction surface. Blow it off, spray the entire racing surface lightly ands you are good to go.
2. Old Asphalt: Grey and hard oxidized asphalt is what most of us race on. All asphalt eventually gets like this. The asphalt gets lighter as oxygen in the air oxidizes the asphalt oils and rain/wind erosion strips off surface oils. To race on this surface blow it off, spray the entire racing surface until it is an even gray color slightly darker than when you started. The soda will soak in. Thats OK all you want to do is keep down the dust you couldn't blow off. Spray the entire track or if a racer gets off line they will run out into "the marbles" and it will take at least a full lap before that get all that dust and junk scrubbed off their tires.
3. Sealed asphalt: Sealer can be sprayed on or painted on with rollers. Many track think this is a good idea but there are lots of problems associated with this. When freshly sealed traction is super high. However,within 12 months the sealer will lose its traction in the racing groove. Natural oxidation and racing will wear the sealer down and you will end up with asphalt with all its pores filled in. This is the lowest traction surface you will ever race on. What ends up happening is ever year you have to re seal. Then you have good traction for a few months...then it goes away. Adding sand to the sealer doesn't help as oxidation, rain and racing will wear the sand away. Eventually you end up with a polished black track that look like the top of an ebony piano. Ripon R/C Speedway in Nor Cal and SRS in Scottsdale are examples of polished track. Luckily both tracts are owned by people that reseal regularly and keep them on top shape. However, ask the owners and they will say they wished they never sealed the track.
Things that help traction:
1. Lots of racing: The more racers the higher the traction from all the rubber getting laid down.
2. Nitro Racing: The rubber from foam tires and the Castor oil from exhaust all improve traction. Remember, traction compounds are mostly oil
3. Traction Compounds: No matter how hot always use something. If you think your fast with no traction compound wait until one guy that knows better shows up at your track and flat out spanks all the locals. Trinity Tire Tweak is great for hot days on asphalt on any tire. If its night racing or cooler weather try Paragon Ground Effects or FXII.
4. Softer springs, more chassis roll, more chassis flex: All of these generate more traction. Save the 3mm chassis and top deck for carpet season. There is a reason why Xray and HPI just released 2mm chassis kits for their cars. I bet sooner than later AE will have a 2mm or 2.5mm chassis and flexy top for the FT TC4. The Schumacher Mi2 has always been 2mm or 2.5mm