The impact of hog manure on organic hemp yield

New organic hemp growers are sometimes mistaken in thinking that hemp can be grown in a wide range of soil types that contain few nutrients. The reality is quite the opposite, as hemp is a nutrient-sensitive plant that quickly responds to increased levels of soil fertility. Providing adequate nutrients in organic hemp production via nutrient-rich fertilizer is the key to maximizing yield.

Data collection through testing

Almost all the research showing hemp yield responses to increased nutrients is done under conventional conditions where inorganic fertilizers are applied. Few studies highlight the importance and challenges that organic growers face when attempting to provide a balanced supply of nutrients to a hemp crop.

Hemp Genetics International (HGI) has gathered data from an organic hemp field in Southern Manitoba where there were variable rates of hog manure applied due to a malfunctioning manure applicator. The liquid manure rate was 7,250 gallons/acre, compared to a control where likely no manure was applied.

Hemp grain yield and soil samples were taken from the treated and non-treated locations of the field (see photo). The control yielded 223 lbs/acre, while the treated section of the field yielded 835 lbs/acre.

Soil samples to 24 inches were taken from each of the locations on August 18 when the plant had likely removed all the nutrients required from the soil. Results are summarized in Table 1. Residual nitrogen (N) levels varied significantly from 17 lbs/acre in the control to 67 lbs/acre in the treated section. The liquid hog manure nutrient analysis concluded that 181 lbs of N/acre were added to the treated area.

Based on results from other data collected by HGI, reduced Phosphorus (P) levels will often reduce hemp yields. Given the relative similarity in P levels between the two soil tests, the P level likely did not have an impact on yield.

Nitrogen makes the difference

This simple data set shows the difference liquid hog manure applications can make in organic hemp yield and, ultimately, the economic return to the organic producer. When soil fertility levels are low, organic hemp producers should consider applying manure, compost, or other organic fertilizer sources to improve yield. This strategy should be complemented with a well-designed green manure addition in the rotation to improve soil fertility and biology.

If you have any questions about these observations or other organic soil fertility research conducted by HPS, contact Alden Braul at (Cell: 204-979-7457).

Visible growth differences between untreated hemp (left) and manured hemp (right).

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