Question
Hi, my name is Philip Ros and I have a science project and would like to ask for your help. I am studying the effects of using an acidic, basic, and salty waters on grass. So far, the acidic water fed (10 percent vinegar), and the basic water (10 percent ammonia) have not shown any growth for the past 2 weeks. Do you think there is a problem? Also, could you give me your opinion on what you think should have happened?

Thank you for your time!

Answer
Vinegar is highly acidic (natural pH of 3). Even in a 10% solution it is likely to produce a very acidic condition. Grass grow well in a very wide range of pH values between 4.5 to 8.5. At very low pH concentrations the heavy metals in the soil (zinc, aluminum, etc) which are needed by the plants in small quantities (fertilizer) becomes highly soluble and is likely to kill the grass. Unless you have seen the grass die off, however, it is more likely that the grass is not affected by the pH change. This could be for various reasons. The most likely reason is that the soil may contain natural buffers (also referred to as the soil's buffer capacity or alkalinity). These buffers (often calcium and magnesium) will prevent high pH swings even if very acidic or alkaline materials are added to the soil. Thus eventhough you add vinegar it is likely that soil is buffered again rapid pH changes.

Therefore, vinegar, if it does not kill the grass, is unlikely to change the growth habit of the grass either. it is not a fertilizer source, and grass is capable of growing in a very wide range of soil pH which anyway is buffered by the soil.

It would be different for ammonia. Ammonia, as opposed to vinegar, is a fertilizer (contain nitrogen). It is likely that the ammonia would act as a fertilizer and prompt a flush growth. This flush grow is normal when highly soluble fertilizer are added to grass. Grass is a "nitrogen pig" and respond immediately to fertilizing with flush growth. This, more than the pH, is probably the cause of your growth. The growth would happen at a pH of 4.5 and 8.5.

Salt solutions (sodium chloride Na+Ci-) also is not a fertilizer, although both Sodium and Chloride are needed in extremely small amounts by plants. These are part of the so-called MICRO nutrients. e.g. needed for plant growth but needed in very very small amounts. typcially they are available in acceptable quantities in the soil already and you gain nothing by adding more (in fact, all you risk is a toxicity to these nutrients if concentrations becomes too high).

Nitrogen (which ammonium is) is a so-called MACRO nutrient together with phosphorus, potassium, calcium, mangnesium and sulpur. These nutrients are needed in greater amounts, e.g. the grass generally tend to deplete the natural resources in the ground requiring gardeners to add these nutrients manually. This as opposed to the micro nutrients which generally do not need to be manually resupplied.

Nitrogen will prompt the grass to grow. The others (vinegar, sodium chloride, e.g. table salt) will not.

Salt can have the unintended effect of pulling water out of the grass plants.

When soil is watered (including watered with fertilizers and/or salt solutions) these solutions enter the roots.

Water and dissolved fertilizer ions (including salt ions) will normally travel from the soil into the roots through a process called osmosis (water travel from high to low concentrations). If the concentration of the moisture in the soil outside the roots contain very high levels of salt the opposite will happen. the water in the plants will escape to fill the low concentration outside (e.g. high salt concentration = low water concentration)

This, in effect, starves the plants. Thus, I would not expect salt water to improve grass growth. In fact, large quantities of salts in the water may prevent it from taking up water and nutrients and kill it.

In summary:
- pH is important for grass plants. Too low and several heavy metals (micro nutrients) can become toxic to the plants. Too high and key macro nutrients (especially nitrogen and phosphorus) becomes unavailable. In most cases, however, grass will grow over a wide range of pH values.

Salt water (Sodium Chloride, or NaCI) has the side effect that it may prevent grass from taking up water and fertilizer and thus can kill it. Besides from this, no growth flush is anticipated.

Vingegar will have no direct fertilizer effect, but as mentioned at very low pH values (vinegar will lower pH drastically) heavy metals can become toxic to the plants.

Ammonium is a natural fertilizer and high in nitrogen, the most important fertilizer nutrient for grass. When fertilized with high levels of ammonium the grass will start to grow. I would expect the grass to turn dark green and show large flush growth.

Kenneth