Here we will discuss what might be called "substrate" influences: the growing medium used to support the plant, and into which the roots will grow; the primary nutrient/fertilizer formula which feeds the plant’s roots; and the method of delivery of nourishment to the plant’s roots.

It is important to remember that this analysis will be based on only 158 reports from the historical Yield-O-Rama database. Thus, for example, there are no reports in which an aeroponic system was used, even though it is well known that such a system is one of the most effective for large, fast growth and lush flowering. In other cases, there are sometimes too few reports (e.g., 1) using a particular ‘substrate’ for it to be a statistically significant influence, even though the variable may look influential when displayed in a bar graph. Such is the nature of things when we’re dealing with a limited data set. :-o

[NOTE: I have attempted something new in the following graphs. I attempted to label the bars with numbers inside the bars, near the tops of the bars. These numbers indicate the actual value on the lefthand, vertical axis, so that people don’t have to try to figure it out by scanning from the axis over to the bars. But I think the numbers inside the bars are a bit hard to read when the graphs are viewed embedded in the HTML document. The numbers show up a lot better if the graph file is viewed in a typical picture viewer, which you might want to use if you want to see these numbers more clearly. Next time I’ll try to do something a bit more legible.]

First, let’s examine the influence of the general "medium" variable, which consists of four categories:

Hydroponic (HYDR), which consists of either a liquid or a dry/powdered nutrient formula dissolved in water and then delivered to the plant.

Fortified (FORT), which consists of a medium in which some minimal starting amount of nutrients may be included in the growing medium, but which must be supplemented or replaced over time by adding a significant amount of nutrients regularly.

Soil (SOIL), which usually consists of soil containing enough nutrients (e.g., potting soil) so that, although eventually more nutrients may have to be added occasionally, not as much supplementation will be required as would be the case with a "fortified" medium.

Phototron (TRON), which is reserved for those cases in which the Pyraponics medium and nutrient formula are specified. (If a phototron setup is not using the Pyraponics system, then it will be using either HYDR, FORT or SOIL.)

Here is a basic graph showing the influence of MEDIUM on crop yield (WEIGHT):

It is evident from this graph that there is a nice, linear relationship between the types of media and average crop yield (grams per sq. ft.). Hydroponic media are clearly superior, followed by a fortified medium (which is actually usually sort of a modified hydro setup), then soil and, finally, the phototron/Pyraponic system. (Note: although there is only one report using the TRON medium, I have it on good authority that the grower actually had several other previous grows using the phototron system, of which this is the best. So I think the single TRON data point is probably reliable.) SOIL is used in 32 reports, FORT is used in 14 reports, and HYDR is used in 111 reports.)

Next, let’s take a closer look at growing media by examining the YOR’s "cypher 2" field: Primary Medium or Soil Mix. The categories of this field have rather long descriptors, so we will not be able to include the descriptions in the graph’s axis labels. Instead, we will first list them here, reproduced exactly as they appear in the YOR data dictionary, with their corresponding alphabetic letter codes. The letter codes in the first column will appear as identifiers on the graph axis:

Any codes listed above but not appearing in any of the 158 reports we are analyzing will not appear in the graph’s axis. Also, the "-" or "N/A" code will be excluded from the graph.

At the high end of weight, we see things such as hydrocorn, lava rock and coconut fiber. At the low end we see things such as unfortified soilless mix and various types of soil mix. However, remember that some of these specific media types are typically seen in combination with only one or two categories of the general "medium" variable discussed earlier (HYDR, FORT, SOIL, TRON). For example, the "multiple media" category (cypher 2 letter code ‘M’) appears only in grow records using the general ‘HYDR’ medium. Here is a graph that clarifies this relationship:

In fact, because of limited sample size (158 records) and the limited number of reports using a particular medium/mix, the above graph portrays the only statistically significant influence of media mix on crop yield. I.e., while the earlier graph showed "Other, not listed" (cypher 2 ‘O’ code) as producing the highest average yield, there is only one report having the ‘O’ code, and this is not enough to draw a statistically reliable conclusion.

The best way to summarize these initial findings is probably to say that a medium/mix that provides for a bountiful supply of oxygen to the plant’s roots, and that does not allow the roots to remain too wet for too long, will generally result in better crop yield.

Next we will examine the "cypher 5" field, which includes various types/brands of hydroponic and soil fertilizers. Before showing the graph, here are the letter codes that will be shown in the X-axis of the graph, as well as their original descriptions from the YOR data dictionary:

As before, only the codes from the above list that actually occur among our 158 records will be shown in the graph; and the "-" or "N/A" code is omitted:

From the above graph we can see that, in general, the hydroponic nutrient formulas are associated with higher crop yield, and the soil nutrient formulas are associated with generally lower crop yield.

However, keep in mind that hydroponic nutrient formulations tend to be associated with the HYDR or FORT categories of the general "medium" field, and the soil fertilizers obviously are associated more with the SOIL category of the general "medium" field, so there is a bit of a "confounding" here. The following two graphs help to clarify this relationship a bit more. The first graph shows the relationship between general medium and crop yield (weight) when using General Hydroponics Flora Series liquid formulation:

Here we see that the GH Flora liquid series is associated with the HYDR and FORT categories of the general "medium" variable. So although this brand tends to produce somewhat higher-weight crops when used in a HYDR setup than when used in a FORT setup, we can’t really say that this is due to the brand. It may be due just as much to the difference between a HYDR and FORT medium in general. Here is a crosstabulation that shows the number of grow reports by medium and by whether GH Flora series nutrients are present vs. absent:

Here’s another graph that also helps to clarify what’s going on. This graph shows the relationship between "medium" and "weight", factoring in the presence/absence of General Hydroponics formulas other than the Flora series:

The above graph indicates a statistically significant influence of the GH nutrient formulation (non-Flora series) in the HYDR category of growing medium: When the brand is used, it results in significantly larger yield than when it is not used. The difference is 10 grams per square foot of canopy. (Note that the only grow reports that indicate the use of GH non-Flora series nutrients are those using a general medium of HYDR.) Although it is not specified in the YOR data dictionary, I don’t think it would be unfair to characterize the GH non-Flora series as "GH MaxiGro" or, more likely, "GH MaxiBloom" nutrient formulas. These would be expected to produce higher yields than the Flora series, and in fact in our data they do (45 vs. 36 grams per square foot in the HYDR ‘medium’ category, which is the only ‘medium’ category where we can directly compare the two nutrient series).

And here is a graph showing that those HYDR reports that use a "brand X" dry nutrient formula have significantly lower crop yields than those reports that don’t use it:

In general, it appears that there’s a good reason that GH brand nutrients are preferred by professional growers of non-marijuana crops. Hey, if it’s good enough for them, then I guess maybe there’s a lesson here for us; and our data tend to support it. J

Next we will consider the various ways that crops can be irrigated, and what this implies for crop yield. As before, we will first show the original definitions from the YOR data dictionary, and the associated letter codes (which will be used to label the X-axis of the next graph:

As before, only those codes that actually show up in our 158-record database will be shown in the graph; and the "-" or "N/A" code will be omitted from the graph:

From the above graph, we see that the Nutrient Film Technique (NFT), the top-feed Ebb-and-Flow method and, particularly, the constant-flow top-feed method tend to yield superior results. In contrast, the active, non-draining technique and the manual irrigation method produce the lowest average yields. To add some clarification, here is a supporting graph that shows the only significant interacting influence between general "medium" and irrigation technique on crop yield:

Here we see that the Nutrient Flow Technique (NFT) is used only in true hydroponic setups and, when used, increases crop yield by about nine grams per square foot of canopy. One might perhaps reasonably conclude that those irrigation methods that provide more nutrients per unit of time, while at the same time providing the plant’s roots with sufficient oxygen, will tend to outperform other methods.

The combined results of the above four sets of analyses (general medium, primary specific medium / soil mix, primary nutrient formula, and irrigation technique) suggest strongly that superior crop yields are produced by growers who: (1) use a hydroponic system with (2) a medium that gives the plant’s roots plenty of oxygen; (3) use GH brand nutrient formulations; and (4) employ an irrigation method that maximizes nutrient delivery per unit of time without depriving the roots of a good oxygen supply.