The nitrogen content in compost holds a top spot in terms of importance during compost production. It influences the activity, nutritional value of the compost, and the progression of all processes from start to the final Phase 3: fermentation, caramelization, pasteurization, and mycelium growth. Consequently, it directly affects the yield and quality of the mushrooms.

The main sources of nitrogen in compost production are straw, chicken manure, and synthetic additives (urea, ammonium sulfate). Straw has relatively stable nitrogen levels, fluctuating between 0.4-0.6%. Chicken manure comes in two types: dry, typically from free-range broiler chickens, and wet, usually from caged laying hens. From my experience, the nitrogen content in dry manure is slightly higher than in wet manure, though there are exceptions. The range varies from 3.5-6.0% nitrogen in dry manure and 2.5-5.0% in wet manure.

Synthetic additives contain a high amount of nitrogen. Urea has 46% nitrogen content, and ammonium sulfate contains 21%. The high nitrogen content is what makes the use of these additives risky.

The target nitrogen level for compost production is 1.8-2.2% in the finished Phase 1 compost.

So, how do we correctly calculate the required amount of nitrogen when formulating the compost?

Rule 1: Measure

If we can measure it, we can control it! A laboratory is essential. We need reliable and accurate data.

Rule 2: Proper Sampling

To get accurate data from the lab, the samples must be collected correctly and represent the entire batch of raw materials used.

Rule 3: Amount of Manure

To achieve good compost quality, we cannot add an unlimited amount of manure. Excessive manure will negatively affect the compost quality. I believe that exceeding 800 kg of dry manure per ton of straw is unnecessary.

Rule 4: Use Synthetic Additives if Necessary

Synthetic additives are useful when we’ve reached the limit for manure but nitrogen levels are still low. Urea or ammonium sulfate can be used. Urea is better suited for liquid chicken manure, and ammonium sulfate for dry manure due to application differences. The key here is uniform distribution: pay close attention to the preparation of the mixture.

Rule 5: Accurate Calculation

Let’s break down an example to calculate the amount of nitrogen needed for compost.

• We start with 1 ton of straw that has:
  • 15% moisture
  • 0.5% nitrogen

Our goal is to reach 2.2% nitrogen in the compost (Phase 1).

The manure we are using has:

• 45% moisture
• 3.5% nitrogen

Step 1: Calculate the dry matter in the straw
First, we remove the moisture to get the dry weight:

• 1 ton of straw (1000 kg) – 15% moisture
  = 850 kg of dry matter in the straw.

Now, we calculate the amount of nitrogen in this dry matter:

• 850 kg of dry straw × 0.5% nitrogen
  = 4.25 kg of nitrogen in the straw.

Step 2: Calculate the dry matter in the manure
Next, we remove the moisture from the manure to get its dry weight:

• 800 kg of manure – 45% moisture
  = 440 kg of dry matter in the manure.

Now, we calculate the amount of nitrogen in this dry manure:

• 440 kg of dry manure × 3.5% nitrogen
  = 15.4 kg of nitrogen in the manure.

Step 3: Combine the dry matter and calculate total nitrogen
Now, we combine the dry matter of both straw and manure:

• 850 kg of dry straw + 440 kg of dry manure
  = 1290 kg of total dry matter.

Then, we add up the nitrogen content:

• 4.25 kg of nitrogen (from straw) + 15.4 kg of nitrogen (from manure)
  = 19.65 kg of nitrogen in the mixture.

Step 4: Calculate the nitrogen percentage in the mixture
To find the nitrogen percentage in the mixture, we use the formula:

• (19.65 kg of nitrogen ÷ 1290 kg of total dry matter) × 100
  = 1.52% nitrogen in the mixture.

Since we need 2.2% nitrogen, we clearly need to add more nitrogen using a synthetic additive.

Step 5: Add ammonium sulfate to increase nitrogen
To reach 2.2% nitrogen, we need an additional 8.73 kg of nitrogen. Ammonium sulfate contains 21% nitrogen, so we calculate how much ammonium sulfate is needed:

• 8.73 kg of nitrogen ÷ 21% (0.21)
  = 41.57 kg of ammonium sulfate required.

Final Result:
To achieve 2.2% nitrogen for 1 ton of straw, you need:

• 800 kg of manure
• 41.57 kg of ammonium sulfate

You can also use the figure for how many kilograms of nitrogen per ton of straw. This figure is convenient for monitoring the dynamic changes in nitrogen application and adjusting from batch to batch. It is usually 24-26 kg of nitrogen per ton of straw.

But remember, compost does not like sudden changes, so it’s best to make no more than one adjustment at a time.