Where is it that you actually are?

We are lucky in the US that the government set up a system with the state universitys of an agricultural cooperative extension service. I think my soil tests were $7 each and if I only wanted to find out about pH and lime requirement, it would have only been $3 each. You might be able to get your hands on some home soil testing stuff but they can be tricky to use and sometimes not very accurate.

Compost does help neutralize (so long as it isn't full of peat moss or potting mix.)

If you truly can't get any testing done, you could try some experiments on a small scale to help you decide what you should do. (with lime or anything to change pH, always go slow and be patient since overdoing could be way worse than doing nothing at all.) Do some research about what kinds of plants that grow in your area like. Some plants can be a good indication about soil pH and other soil conditions. Around here azaleas like more acid soil. Peas and Beans supposedly should not be planted in acid soil.

Problem with trying these types of tests is that though the plant may suffer in extreem acid conditions, it still may do just find in only slightly acid conditions. There are also so many other factors involved that it can be difficult to carry out a really meaningful test. You might try using a small amount of lime in one section of garden and see if the plants in that area do better than the others (this could be misleading if that section of garden has other different conditions-water, sun, wind, soil- but you gotta start somewhere. Keep in mind such a test will take a long time to show any change since lime is usually slow acting on the soil pH so keep some garden notes.)

As to rainfall, if the rain is not acid rain and the atmosphere it is falling through does not have a lot of pollution for the rain to pick up, it should be fairly neutral. If your soil is acid only because of stuff that was added to it, the rain should help leach some of this away returning your soil to it's original condition (very slowly.) However, if your soil is naturally acidic, the rain will have the effect of leaching away what you add to it. They generally say that making a big change to the pH of natural soil is difficult and usually short term.

Keep in mind, most garden plants do just fine within a pH range of 6-7 which is slightly acid. Most potting mixes are more acid than that I've measured potting mix at 5-5.5 (due to high amounts of peat in the mix) and plants still did fine. So unless you are trying to grow plants that like a very high pH or dealing with really acid soil to start with, your lime requirement is probably pretty low. For some situations, the lime is more to add calcium to the soil than strictly for the pH.

Good luck

I'm not sure why manures would necessitate adding lime. In fact, my understanding is that animal manures can raise the pH of soil. I live in an arid area with high pH soil (more on that later), and we're cautioned against using animal manures too much for two reasons. One is the pH and the other is salinity.

With enough rainfall, the salinity is not an issue. It's only an issue in arid areas.

Areas of high rainfall tend to have acidic soils and areas of low rainfall tend to have alkaline soils. Rain does leach some things, but the result is that what remains is more acidic.

You may need to add lime, but it would be because of the other factors, not because of the manure. If anything, the manure is making the lime less necessary.

@tclynx
I come from Malaysia, a country in Southeast Asia about 2.5 degrees north of the equator. Residential organic gardening here is pretty much in the "dark ages" and most people simply equate it to throwing animal dung around :P. So unfortunately I do not have access to agricultural cooperative extension services. There *is* one home test kit available, but it's imported (read expensive) and, as you say, they don't necessarily give accurate results anyway.
I guess you are right about the multitude of factors involved besides the pH. So perhaps I shouldn't try to fix what is not yet broken till I get a proper soil test done....somehow.

@bpgreen
"In fact, my understanding is that animal manures can raise the pH of soil."
Is that true? I Googled "garden lime" to find its purpose and stumbled upon a site which said the opposite:

" To raise the pH and lower acidity or sweeten the soil, we add lime. To lower pH and increase acidity you can add sulphate of ammonia or urea which are high nitrogen fertilizers.
From this you can see that adding manure will also lower pH and make the soil more acid.
ItÂs counter to what you expect, but adding loads of manure year after year will actually reduce soil fertility by making it too acid so the plants cannot access the nutrients. They become locked up."
http://www.allotment.org.uk/articles/Garden_Lime.php

Please help me sort out the misinformation :)

OK, I donÂt want to start a big fight with the previous posters, BUT rain tends to be slightly acidic no matter how pristine the environment. In industrial areas it can be very acidic.

In addition to the acid the rain adds to the soil, the basic cations in the soil (calcium, potassium, magnesium, sodium) will readily leach out of the soil profile. This is particularly prevalent in areas where precipitation exceeds evapotranspiration, such as Malaysia.

You say you have a lot of clay which indicates significant weathering. Not surprising considering you are in the tropics. Well developed soils typically do not have a lot of basic cations which were lost in the weathering process. Also, depending on the parent material there may or may not have been much in the way of basic materials to start with.

Compost and manure can raise pH in the short term by supplying salts (calcium, potassium, sodium) and ammonium. However, decomposition is an acidifying process and in the long run will lower pH. It is a misconception that compost will Âbalance the soils pH. Compost will buffer the pH; that is it will help the soil resist changes in pH, but it is not a liming material.

Unless you are in a limestone area, it is a pretty safe bet that your soil could use lime. How much would depend on your pH, and amount and type of clay.

I said the same thing about the rain, so no argument here.

I made my comments on the manure raising the pH based on some vaguely remembered info from a long time ago from the extension service here. Manures are different from urea and ammonium sulfate (although the chicken manure contains some urea).

If the decomposition process acidifies, then the soil is pretty sure to be pretty acidic (especially considering the high rainfall).

if you can get your hands on dolomitic lime in powder form you can't overuse it. the stone it's self has a ph of 7 and can't overdue it as long as you don't get seriously out of hand with it. usually the rule of thumb is to use about 15% lime to any volume of soil. My experience has been best using horse manure and beef cattle manure because the structure of the manure is basically ground up straw or grains and is high in nutrition especially Nitrogen. these manures also break down very quickly when properly composted and rotated.

Chicken manure is a tricky subject. horse and cow manure are ready to use in a week from creation but chicken manure is much "hotter" meaning it is too full of nutrients to be used by plants. if the manure was rained on and then dried in the sun it would be usable becuze the urine has been leached into the water and run off. you can artificially do this by wrapping the manure in a large sheet or piece of fabric and submerging it in water for 24 hours. then the water is poured off and the manure must be dried in the sun on the sheet or a tarp. thats why i like horse manure best, easier to leach and deal with.

Most nurseries and hardware stores have litmus paper and soil tests for under $10.

"if you can get your hands on dolomitic lime in powder form you can't overuse it. the stone it's self has a ph of 7 and can't overdue it as long as you don't get seriously out of hand with it."

That sounds good. Where else would I be able to obtain it, if not from gardening stores? Would regular garden lime be a reasonable substitute?

"Most nurseries and hardware stores have litmus paper and soil tests for under $10."

As explained in a previous post, I have seen a soil test kit (in vial form) for around that price, but am not certain of its accuracy (Rapitest, I think). And USD10 converted to my currency can feed me for 4 days :)
Most "experienced" gardeners in this area don't even know what pH is. It's mostly trial and error and hand-me-down tips from grandma (which of course is fine when it works).
I guess I wouldn't mind investing in one of those kits if someone could tell me that it's fairly accurate.

A relatively simple test you can do that would give an indication of your soils pH is to rake a small amount of wet soil and pour some vinegar on it and if you see bubbles form that woul indicate an alkaline soil while putting a mixture of baking soda and water (a thin slurry) causing bubbling would indicate an acidic soil. Not nearly as good as a good, reliable soil test but about as good as one of the inexpensive pH meters on the market to day.
Whether to add lime depends on which lime you need to add, is your soil lacking in Calcium or is the Calcium/Magnesium ratio out of wack? Adding a Calcitic lime to a soil with an unbalanced Ca/Mg ratio will do little if the Magnesium levels are low. Adding Dolomitic Lime to a soil with more than ample levels of Magnesium will only result in greater unbalances of the Ca/Mg ratio increasing your soil problems.
Over time compost, and organic matter, can balance both the soils pH and nutrient load, but too much organic matter in soils creates other problems.

"if you can get your hands on dolomitic lime in powder form you can't overuse it. the stone it's self has a ph of 7 and can't overdue it as long as you don't get seriously out of hand with it."

This is not true. Dolomitic lime is just like calcitic lime except it has some magnesium in it. You can very easily over use it. Every bit of lime you add to your soil is adding basic cations and every bit you add will raise the pH.

Without knowing your starting pH and your soils buffering capacity it is a total wild guess, but I would say till in 1/4 kg ag lime per square meter. If it seems like it helped repeat every 3 years or so.

In the Tropics I doubt very seriously if you could ever add too much organic material to the soil. The heat, humidity combined with the very active soil flora and fauna will make short work of any manures. If you are planting beds for ornamental plants I would just keep adding mulch 3-4 times per year and your soil will be healthy. If you are planting food crops, tilling in compost and/or composted manure will pretty much balance things out from a pH perspective.

"tilling in compost and/or composted manure will pretty much balance things out from a pH perspective."

Again, this is a common misconception. As you said the environmental conditions in the tropics will rapidly decompose an organic material which is an acidifying process. There might be a short term increase in pH from added bases, but in the long run the pH is going to drop. Pretty much everything in a natural soil system results in acidification including microbial activity, rain, leaching, and growing plants (and most nitrogen fertilizers). The only thing that will raise pH is the addition of bases. These can occur naturally from the weathering of basic parent materials (rocks) or by adding them ie liming usually with crushed rocks). I realize that people like to think of organic matter and compost in particular as a cure all, and it certainly has many benefits, but raising pH simply is not one of them. If you have acidic soil conditions, lime it. Lime is natural, cheap, available, and effective. Throw some in your compost while you are at it, it will benefit as well.

"Lime is natural, cheap, available, and effective. Throw some in your compost while you are at it, it will benefit as well."

It is not advisable to add calcium carbonate to the compost since it will increase the pH. As the pH increases, ammonium cations change to volatile ammonia gas with a resulting loss of nitrogen nutrients.

The addition high CEC materials such as clayey soil, clay slurry, or zeolite will hold the nutrient cations and improve your compost's nutrient content.

"It is not advisable to add calcium carbonate to the compost since it will increase the pH. As the pH increases, ammonium cations change to volatile ammonia gas with a resulting loss of nitrogen nutrients."

This is true, but is really not much of an issue unless until the pH gets above 7 in composts that are high in nitrogen.

"The addition high CEC materials such as clayey soil, clay slurry, or zeolite will hold the nutrient cations and improve your compost's nutrient content."

I guess it depends on your composting objectives; I tend to think of compost as a good soil amendment, not a nutrient source. I realize compost does have some nutrient value and that many gardeners add nothing to their soil but compost. However, if you are a lazy composter like I am and let the rain run through it for a couple of years and donÂt ever turn it and toss some lime on it and you lose half the nitrogen value, you really havenÂt lost much. Quarter pound a pound a yard? Something like that? On the other hand much less effort put into growing a legume cover crop will supply a good deal of nitrogen (as well as organic matter). I have plots 3 feet deep in soy beans right now. This fall I will fork on a few inches of my lazy compost on and I feel I will be much further ahead that trying to make perfect compost.

Thanks for the feedback, everyone. As is often the case, we end up with some differing views. OK, here's my take on the matter, based on some (very limited) knowledge of soil microorganisms.

As I understand it, bacteria prefer an alkaline environment, whereas fungi thrive in an acidic one. Therefore, since typical garden soil is predominantly bacterial, shouldn't the decomposition that they cause produce a pH level conducive to what they prefer? (i.e. alkaline, as opposed to what I had assumed earlier). I'm sure my reasoning is full of holes, so please correct me where I'm wrong.

This page seems to partially support what I said:

http://www.alaskahumus.com/JeffsLectureNotes.htm