Don't trip too much on run-off in organics, there's a bit of misinformation involved with run-off being "bad" for organic soil in the sense that run-off being bad is only "half" true and is situational. If run-off depletes your soil of nutrients, your soil is likely mediocre unfortunately. Please allow me to explain.
Look into Cation Exchange Capacity, or CEC for short. Essentially, Cations have a positive charge and Anions have a negative charge. There are some exceptions to this rule, but for simplicity's sake we'll just leave it at that. Why brings this up? To cite a source;
"Since soils are negatively charged and plant nutrients are positive and negative, some nutrients are attracted to soil while others are not – the “opposites attract” principle. Those nutrients that exist as anions (-) are moved through soil, meaning growers need to be careful how they are applied regardless of soil type. These nutrients readily travel wherever water carries them, leading to nutrient runoff and leaching and economic loss and environmental concern.
Cations (+) are more readily bound to soil, resulting in these nutrients moving through the soil more slowly. However, since low CEC soils have fewer negative charges, cations will move more quickly through low CEC (sandy-based) soils than they will through high CEC (loamy and silt/clay-based) soils."
Think of Cations and Anions as the positive and negative sides of a magnet, this is exactly what's happening in your soil.
Run-off is only an issue once you top dress, once the top dress has decomposed then having run-off will cause little to no issues. Let's say you just grabbed yourself a bag of Dr Earth's Tomato and Herb blend to top dress your soil with. This is where run-off becomes an issue, because if you aren't careful with watering then you'll literally wash your top dress off the soil and it will be useless because it hasn't had a chance to decompose/work itself into your soil. So you need to water carefully until the top dress has decomposed/worked it's way deeper into the soil. Once the organic amendments are decomposed, they become nutrients in the form of Cations and Anions. Amendments mostly have a positive charge, though a small percentage will be negatively charged. For sake of example, lets just say decomposed amendments are 80% Cations and 20% Anions. Remember the magnet example above? The bulk of the nutrients in your top dress will literally bind themselves to the soil in a reaction similar to that of a magnet. The soil is like a negative magnet and your amendments are a positive side of the magnet. The 80% Cations will bind themselves to the soil and all the water in the world will not remove this bond. The 20% that are Anions, however, will run-off with too much water.
There is, however, one exception to this in the form of Phosphorus.
"The odd anion is phosphorous. Even though it has a (-) charge, it is not mobile in soil because phosphorous forms are not very soluble. It can, however, still move – not as the anion, but bound to soil particles as the particles move. Therefore, minimizing runoff is helpful in reducing phosphorus pollution." This is part of the reason that Coot's recommends keeping Phosphorus levels low in your soil (NPK value for P should be less than
. Pollution/toxicity will only be an issue for you if you're top dressing with something strong, like Fish Bone Meal (3-16-0) or Seabird Guanos, aka "hot" amendments.
This is exactly why people use Peat Moss in organic soil as opposed to Coco. Coco is infinitely more forgiving than Peat Moss is in terms of watering, however Peat Moss has double the CEC that Coco does which means that Peat Moss can "hold" more nutrients than Coco can because Peat Moss is a more powerful "magnet" than Coco is.
I'll cite a few more sentences, and sources are below for you all to review
"Plant nutrients exist in the soil as either anions or cations. What are they? Most molecules in natural systems have a positive or negative charge and it is this charge difference that helps drive chemical reactions to keep us all alive – that’s important. Anions are those elements or molecules that in their natural state have a negative (-) charge. Cations are those that in their natural state have a positive (+) charge. Negative charge, positive charge – who cares? Keep reading.
Most soil particles have a negative charge. The amount of negative charge depends on soil texture, such as sand, silt and clay content, which is directly related to soil particle surface area. The cation exchange capacity (CEC) determined by a soil test is a direct indication of the amount of negative charges on your soils. A soil with low CEC has fewer negative charges than a soil with a higher number. High sand soils generally have a low CEC, clay or silt soils are higher and organic soils are highest – all related to particle surface area."
"When applying nutrients to low CEC soil, it is best to apply a little at a time otherwise you run the risk of leaching them through the soil and into ground water, especially on seasonally high water table sites. When applying nutrients to clay soils, due to their naturally slow infiltration rate, it is best to incorporate them. If they are placed on the surface they are prone to run-off during periods of heavy rain (or overhead irrigation) and contaminating surface water."
https://waltsorganic.com/cation-exchange-what-is-it-and-why-is-it-important/
https://www.canr.msu.edu/news/what_is_your_soil_cation_exchange_capacity
https://www.canr.msu.edu/news/anions_and_cations_in_plants_oh_my_but_why_do_we_care
tl;dr: If your soil is made of peat moss and is of high quality, you won't lose much nutrients via run-off.
