Industrial hemp is generally described as an excellent scavenger of nutrients from the environment, however anecdotal evidence also suggests that when nutrients are readily available hemp will undertake a luxury feeding type behaviour taking up nutrient not required for crop production). This excessive nutrient uptake, particularly in the case of nitrogen, promotes stem elongation and soft stems which are prone to lodging, both of which have a negative impact on the harvestability of the crop.
Midlands has recently completed a series of trials investigating the effects of both row spacing, plant population and nitrogen fertiliser inputs on the grain yield of industrial hemp cultivars in the New Zealand environment. The cultivars utilised for this work are northern hemisphere breed cultivars represented by Midlands in both the New Zealand and Australian markets.
Trials were undertaken over two seasons, with individual trials completed each season evaluating different phenomena: one trial investigating row spacing and plant population, and a second trial investigating nitrogen inputs and planting timings. Row spacings were completed at 15 and 30cm with target plant populations of 100 pl/m2 and 150 pl/m2 at each spacing for three cultivars (CRS-1, CFX2, and Ferimon 12). Nitrogen treatments were applied over 8 cultivars representing both grain, multipurpose and fibre type cultivars (CRS-1, CFX2, Katani, Earlina 8FC, Ferimon 12, Fedora 17, and Futura 75). Treatments were based on soil mineral N tests taken at the time of sowing with low nitrogen treatments allowing for 130kg of soil available N/ha and high fertiliser treatments allowing for 200kg of soil available N/ha. These available N rates were achieved through a combination of the soil mineral N and applied N in the form of urea.
The results of these trials show that a lower N input has minimal effect on the grain yield of the industrial hemp cultivars assessed whilst increasing the harvestability characteristics of the crop (decreased height etc). Increased row spacing also showed no effect on the grain yield of hemp cultivars in the trial, but the more open canopy of wider row spacings did increase weed pressure. Plant population also showed no effect on grain yield in this work. The largest driver of yield differences seen in these trials was the cultivar grown, adding further weight to cultivar selection being hugely important in industrial hemp agronomy.