nutrient analysis and fertilizer recommendations

Tuesday, February 6, 2007

Today I finally got to analyze my results myself to figure out what it all meant!!! The testing kits themselves had a surprising amount of information regarding the recommended soil concentrations for the major essential nutrients for plants that are found in soil; N, P, K, Ca, Mg, and S. So basically, first I did a bit of research on why their presence is so important for plant (particularly grape) growth, then I looked at their fertilizer recommendations (since adding fertilizers would raise/lower concentrations in order to approach the recommended optimum levels). Based on these recommendations, I was able to then formulate exactly how many bags of which fertilizers we should buy in order to reach these levels given how large the CZ vineyard is. Very exciting stuff!

Here are some basic facts I found about …

N (nitrogen): probably the most essential element for plants biochemical processes as a component in chlorophyll. It enhances above-ground growth, hastens plant maturity (as long as levels aren’t excessive), and is very influential in fruit sizing. However, too much nitrogen can cause excessive growth, which would not be good particularly for growing grapes for quality and not quantity.

P (phosphorous): also hastens maturity, encourages root development, and increases its resistance to disease. If concentrations are low, it can retard plant growth and lowers its vigour. However, unlike N, an excess of it is ok. P is often gradually depleted with cropping, so it must be replaced with phosphate fertilizers if concentrations are too low.

K (potassium): is an important basal metal cation in plant biochemical functions as it enhances disease resistance as well as fruit size, flavour, texture and development. Usually soils with high clay content have higher potassium content whereas sandy soils or those with little/no clay have low native K levels and are subject to severe leeching and annual K applications are required. (This is common in the S.E. US areas). The test we used measured for available K, which include the exchangeable colloids and potassium in the soil solution.

Total Ca (aka replacable calcium): concentrations can range from 0.1 to 25% in the soil and has a direct correlation with the acidity of soils. Acidic soils (usually found in the eastern half of the US) tend to have low Ca levels. Soils with lots of lime in them have high Ca concentrations. Ca is responsible for maintatining optimum pH levels as it reduces the acidity and toxicity of other minerals such as manganese, Zn, and Al. As such, it acts as a stabalizer in soil. It will not limit plant growth, but it effects other things which can. If concentrations are low, it indicates that much of the active Ca in the soil has been replaced by hydrogen or other ions, as in acidic or highly alkaline soils. Ca levels in normal sandy soils are usually around 500ppm; clay soils tend to be 1000ppm; and humus soils (like peats and forest molds) should be around 500ppm.

Mg (magnesium): like calcium, has its source in limestone, so naturally soils found in areas with lots of limestone will tend to have higher Mg concentrations. Mg is essential for plant photosynthesis. If concentrations are low, add limestone (treat with the dolomitic lime fertilizer), which contains lots of magnesia, but if your soil doesn’t need lime, they recommend adding Mg sulfate, Mg oxide or Mg and K sulfate. If concentrations are high/very high coupled with low Ca levels, they recommend treating it with gypsum or high calcite lime, with prevents Ca deficiency because of over-balance of Mg.

Based on our results for Mg and Ca, it appears that we don’t have to do much to the soil as it is already at the levels expected for the area and type of soil we have.
Our K levels were very high, so we also didn’t need to do anything to change K levels. N and P were a different matter, however. The test kit booklet recommended that when growing grapes, the NPK requirements were that they were all (at least/around) medium levels. Since we only found trace amounts of N and P, it’s clear that we need to bring up concentrations by adding fertilizers. Using their convenient chart in the back of their book (which gave their fertlilizer recommendations based on our test results), I found that according to their recommendation of adding 5lbsN/2000ft2 we would need around 145lbs of N, that’s 3.81 100lb bags of nitrogen fertilizer at 38%N (or 38lbsN/ 100lb bag) [given that the vineyard is 1.33 acres or 57,934 ft2]. They recommended we add 6lbsP/2000 ft2 that’s around 174lbsP, which is 3.86 100lb bags of phosphorous fertilizer at 45%P (or 45lbsP/100lb bag). However, Cliff thought that we probably would only need to add 4lbs of each per 2000 ft2 (he interpreted their recommendation chart slightly differently), which would amount to only 3 100lb bags of N fertilizer and 2.5 100lb bags of P fertilizer. And since they are sold in 50lb bags, that would be 6 bags N fertilizer and 5 bags P fertlilizer. However, Cliff said that he knows that the grape vines are already growing quite well without the fertilizer and that excessive nitrogen can cause excessive plant growth (which we don’t need), so he recommends not adding quite so much N and will add probably buy the 5 bags of P fertilizer and only 3 bags of N fertilizer.
Wow! Who knew this would be so much work to figure out how much fertilizer you need! I guess I always just assumed the more the merrier. But now I know that it’s essential to get the right balance for plant growth as well as economics. Fertilizers can be expensive!
After figuring this all out, I also started looking at mapping the vineyard onto the computer. Cliff had set up a database in Access which will record vine locations spacially based on mapping the rows and using trigonometry to find out the UTM (universal transverse mercador) corrdinates of each vine given: the UTM coordinates of the end points of all 23 rows; the angles of the rows of vines to an imaginary xy grid; and the length between vines along the rows (which we will measure out in the vineyard sometime next week, hopefully when it’s warmer). While Cliff had already programmed the formula into the database so that we could plot the location points of each vine once we found the distance along the row each vine was, he wanted to explain to me how he had derived it. Who knew I would actually use my 9th grade trigonometry knowledge of sin, cos, tang, and hypotenuse stuff! I just wish I’d remembered it a bit better... We also took a look at the database entry form itself on Access, which helps him to organize the names, breeds, particular hybrids, parents, and other qualitative and quantitative descriptions of his grapes. By the time we’re done, we will also have UTM coordinates for each vine in the database! That way we can bring the data into a GIS system where we will be able to create various maps of the vineyard and highlight certain data entries for each vine (represented by a point) to make interesting conclusions on data in a visual way or quickly pinpoint where a particular plant might be.