The stock to use ratio indicates the level of carryover stock for any given commodity as a percentage of the total use of the commodity. The stocks-to-use ratio is technically an indicator of supply relative to demand in quantity terms. So when the stock to use ratio goes down, prices go up. Let's illustrate this with some graphs.
Corn prices can be found in the chart below:
When analyzing both charts, we see that when the STU ratio went down in 2010-2011, we saw a price spike in corn a few years later (2011-2012). Then the STU ratio went up in 2013-2014 and consequently we saw a drop in corn prices in 2014-2015. As the STU ratio is topping off again in 2016, I expect to see a rise in corn prices very soon. The rise in corn prices is also supported by the rough weather in Brazil.
Let's look at wheat. The wheat STU ratio has ween going up since 2006, so it's clear we have an oversupply in wheat.
Wheat prices have also been dropping since 2006, with a small upside correction in 2010-2012 when STU ratios went down. Looking at the trend in STU ratio, I don't see a bullish pattern in wheat at this moment.
As for soybeans, we have the following chart. The STU ratio crashed in 2007 and this lead to a doubling of the soybean price in that year. Today in 2016, we see a similar trend where both world and U.S. STU ratios crash down, so I expect that soybean prices will do well going forward. Reports of Brazil having too dry weather and Argentina having too wet weather have supported soybean prices.