Nitrogen fertilization to optimize the greenhouse gas balance of hemp crops grown for biomass

Abstract

Nitrogen trials were carried out on hemp crops grown in Ireland over a 3 year period to identify nitrogen fertilization strategies which optimize the greenhouse gas (GHG) and energy balances of hemp crops grown for biomass. Nitrogen rates up to 150 kg N ha À1 were used in the study. Yield increased with nitrogen rate up to 120 kg N ha À1 for early (Ferimon), mid (Felina 32) and late maturing (Futura 75) varieties. Variety had a significant effect on yield with yields increasing with maturation date. In 2 years of the study, certain application rates of nitrogen were applied either at sowing, at emergence, after emergence or split between these dates to determine if nitrogen rates could be reduced by delaying or splitting the applications. The application of nitrogen at times later than sowing or in splits during the early part of the growing season had no significant effect on biomass yield compared with the practice of applying nitrogen at the time of sowing. Late applications of nitrogen reduced leaf chlorophyll content and height early in the growing season. Later in the growing season, there was no difference in height between treatments although the highest concentrations of chlorophyll were found in the leaves of the late application treatment. Nitrogen rate and the timing of nitrogen application had no effect on plant density. Biomass yield, net energy and net GHG mitigation increased up to an application rate of 120 kg N ha À1 , this result was independent of soil type or soil nitrogen level. Net GHG and energy balance of hemp crops grown for biomass are optimized if late maturing varieties are used for biomass production and a nitrogen rate of 120 kg ha À1 is applied at sowing.

Hemp (Cannabis sativa L.) leaf photosynthesis in relation to nitrogen content and temperature: implications for hemp as a bio‐economically sustainable crop

“…Hemp is considered an ideal annual crop for the bio‐economy as it has the potential to produce a high multipurpose biomass yield while requiring little inputs (Finnan & Burke, ; Tang et al ., ). However, very limited information is available on the physiological basis of hemp resource‐use efficiency.…”

“…The high photosynthesis rate of hemp at low nitrogen condition is in line with its observed high productivity at low nitrogen input (Struik et al ., ; Finnan & Burke, ) and puts hemp ahead of cotton and kenaf from a perspective of bio‐economy. However, our model approach has limitations.…”

A Review on the Current State of Knowledge of Growing Conditions, Agronomic Soil Health Practices and Utilities of Hemp in the United States

“…Previous research also showed that hemp response to P might vary depending on growing conditions [70], and its availability plays an important role in the elasticity and tensile strength of hemp fibers. A study reported that P uptake by hemp ranged from 52 to 67 kg ha −1 , and P fertilization had no effect on stem yield [67]. P enhancement treatment caused a 16% reduction of THC concentration but did not affect CBD concentration in the flowers [71].…”

“…A study reported that 79% of total N uptake occurred within the first month with a daily N uptake of 3-4 kg ha −1 [66]. Another study reported that N application after sowing or applied by split method did not increase stem yield when compared to N distribution at sowing [67]. An increase in 60 kg dry matter (stem biomass) kg −1 N applied was noticed as N fertilization was increased from 0 to 120 kg N ha −1 .…”

“…An increase in 60 kg dry matter (stem biomass) kg −1 N applied was noticed as N fertilization was increased from 0 to 120 kg N ha −1 . However, beyond N fertilization rates of 150 kg ha −1 , no further yield increase was reported [67]. Excess N application stimulates rapid stem elongation which makes the hemp crop more susceptible to lodging [15].…”