The effect of N and P fertilization on growth, seed yield and quality of industrial hemp in the Parkland region of Saskatchewan

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1 The effect of N and P fertilization on growth, seed yield and quality of industrial hemp in the Parkland region of Saskatchewan C. L. Vera 1, S. S. Malhi 1, J. P. Raney 2, and Z. H. Wang 3 1 Agriculture and Agri-Food Canada, Melfort Research Farm, P.O. Box 1240, Melfort, Saskatchewan, Canada S0E 1A0 ( verac@agr.gc.ca); 2 Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2; and 3 College of Resources and Environmental Sciences, Northwestern Sci-Tec University of Agriculture and Forestry, Yangling, Shaanxi, , China. Received 9 February 2004, accepted 11 April Vera, C. L., Malhi, S. S., Raney, J. P. and Wang, Z. H The effect of N and P fertilization on growth, seed yield and quality of industrial hemp in the Parkland region of Saskatchewan. Can. J. Plant Sci. 84: Industrial hemp (Cannabis sativa L.) has sparked renewed interest in western Canada in recent years, and there is very little research information available on its fertilizer requirements. The objective of this study was to determine the effect of surface-broadcast ammonium nitrate and seedrow placed monoammonium phosphate fertilizers on the production and seed quality attributes of industrial hemp (cv. Fasamo and Finola). Field experiments were conducted on a Black Chernozem silty loam soil at Melfort, Saskatchewan, Canada, in 2000, 2001 and Increasing N rates significantly increased plant height, biomass, seed yield and seed protein content of hemp in all years. Seed-applied P fertilizer increased plant height in all years, and biomass in 2000, but reduced plant density, biomass and seed yield in 2001 and Finola consistently had lower plant height, earlier maturity, heavier seeds, and higher seed yield, seed protein content and seed oil content than Fasamo. The average amount of nitrate-n in the 0 60 cm soil was 40 kg N ha 1. Seed yield kg 1 of N was 9.4, 5.9, 4.5 and 3.7 kg ha 1 for Fasamo, and 10.6, 7.7, 6.0 and 4.5 kg ha 1 for Finola, respectively, at 40, 80, 120 and 160 kg ha 1 of soil plus fertilizer N. Key words: Fertilizer, hemp, nitrogen, phosphorus, rainfall, soil extractable P, soil nitrate-n, cultivars Vera, C. L., Malhi, S. S., Raney, J. P. et Wang, Z. H Incidence des engrais N et P sur la croissance, le rendement grainier et la qualité du chanvre industriel dans la région des prairies-parcs de la Saskatchewan. Can. J. Plant Sci. 84: Depuis quelques années, les agriculteurs de l ouest du Canada recommencent à s intéresser à la culture du chanvre industriel (Cannabis sativa L.). Malheureusement, on s est fort peu intéressé aux besoins de cette plante en matière d engrais. L étude devait préciser les effets du nitrate d ammonium épandu à la volée et du phosphate d ammonium diacide appliqué localement sur les paramètres de la production et de la qualité grainière du chanvre industriel (cv. Fasamo et Finola). Les essais au champ se sont déroulés sur un tchernoziom noir de type loam limoneux à Melfort, en Saskatchewan (Canada), en 2000, 2001 et L augmentation du taux d application de l engrais azoté a sensiblement accru la hauteur du plant, la biomasse, le rendement grainier et la teneur en protéines de la graine les trois années de l expérience. L application d engrais phosphaté avec la graine a donné de plus grands plants chacune des trois années et une biomasse plus importante en 2000, mais a réduit la densité du peuplement, la biomasse et le rendement grainier en 2001 et en Finola a toujours donné des plants de plus petite taille, une meilleure précocité et des graines plus lourdes que Fasamo, ainsi qu un rendement grainier, une concentration de protéines dans la graine et une teneur en huile dans la graine supérieurs. La concentration moyenne de N sous forme de nitrate relevée dans les premiers 60 cm de sol s établissait à 40 kg par hectare. Fasamo a donné 9,4, 5,9, 4,5 et 3,7 kg de graines par hectare et Finola 10,6, 7,7, 6,0 et 4,5 kg par hectare, respectivement, avec l application de 40, 80, 120 et 160 kg d engrais N par hectare. Mots clés: Engrais, chanvre, azote, phosphore, précipitations, P extractible du sol, nitrate dans le sol, cultivars Industrial Hemp (Cannabis sativa L.) was developed from wild Cannabis plants that originated most probably in Central Asia over 3000 yr ago (Clarke 1999). These early landraces dispersed to other areas of Asia, Europe and Africa, where they were further domesticated and selected for more specific uses such as fibre, food, and for medicinal and psychoactive properties. Hemp was first brought to the American continent in the 1500s by early European colonists, mainly for rope and sail manufacture, but later direct introductions of superior cultivars from China and India took place in the 1800s. Through the years, hemp has occasionally escaped into the wild and developed into weedy strains. This phenomenon has been observed in eastern Canada, in areas of the St. Lawrence valley and the 939 lower Great Lakes (Small et al. 2003). Extensive research on industrial hemp was done in Canada in the early 1900s (Gehl 1995), with the objective of studying the adaptation and performance of fibre hemp cultivars to the different ecological zones of the country, as well as for identifying the best agronomic practices for its cultivation. Commercial production did not develop well, however, because of competition from lower- priced tropical fibres, and was later prohibited by the Narcotics Drug Act in 1938, although a small production was maintained during the war years (Gehl 1995; Blade 1998). The cultivation of hemp is again being permitted in Canada, but under strict control and monitoring Abbreviations: THC, tetrahydrocannabinol

2 940 CANADIAN JOURNAL OF PLANT SCIENCE by Health Canada. In western Canada, hemp is being grown as an oilseed crop (Hanks 2002) rather than for fibre, and cultivars have been introduced from Europe for this purpose. Hemp seeds contain approximately 30% oil, with a relatively high proportion of the fatty acid gamma linolenic acid, which is presently being investigated for its nutraceutical properties (Pate 1999). It is well established that crops differ in their nutrient requirements (Johnston et al. 1999). Based on European experience and research, Ranalli (1999) reported that hemp grown for fibre has low fertilizer requirements, comparable to those of wheat. Reporting on studies done in eastern Canada, Gehl (1995) indicated that fibre hemp cultivars were very responsive to the addition of commercial fertilizers or manure. Crop diversification is important for the agronomic and economic sustainability of agriculture producers. Hemp is one of the most recent additions to the list of crops now available to farmers, who planted in excess of 1000 ha of this crop in western Canada in As the interest on new crop alternatives increases in the farming community of western Canada, it is important to establish agronomic recommendations for these incoming crops, as very little information is available regarding their nutrient requirements and other cultural practices (Blade 1998). The objective of this study was to determine the effect of commercial N and P fertilizers on the development and production of two welladapted oilseed industrial hemp cultivars to the northern Parkland region of western Canada. MATERIAL AND METHODS Site Description and Experimental Design The study was conducted at Agriculture and Agri-Food Canada, Melfort Research Farm, Melfort, Saskatchewan, in 2000, 2001 and Soil type was a Black Chernozem (Udic Haploborolls) with silty loam texture, and 8.2% organic matter. Other soil characteristics and growing season precipitation are given in Table 1. Mean annual precipitation of the area is 413 mm, of which about 60% occurs in the growing season from May to August. The area has a mean annual temperature of 1.0 C, 93 frost-free days and 1517 growing degree days (>5 C). The experimental design was a randomized complete block, with four replications. Treatments consisted of a factorial arrangement of two cultivars (Fasamo and Finola), four N fertilizer rates (0, 40, 80 and 120 kg N ha 1 ) and two P fertilizer rates (0 and 20 kg P ha 1 ). Nitrogen, as ammonium nitrate (34-0-0), was top-dressed d after seeding, and P, as monoammonium phosphate ( ), was applied with the seed. The experiment was seeded into cultivated land, using a double-disk plot seeder, with 2.5-cm seeding depth. Seeding dates were 2000 Jun. 01, 2001 May 22 and 2002 May 28. In 2002, the experiment was reseeded on Jun. 21, because the original test was affected by volunteer wheat (Triticum aestivum L.) and canola (Brassica napus L.) plants. Previous crops were wheat (T. aestivum L. AC Taber ) in 1999 and 2000, and canola (B. napus L. Conquest RRT M ) in Each plot consisted of seven rows, with 18-cm row spacing and 4.2-m row length. Seeding rate was 280 viable seeds m 2. Leaf and inflorescence plant samples, were removed from a hemp cultivar experiment growing at the same site as the present study, bulked and dried at room temperature for Delta 9 Tetrahydrocannabinol (THC) analysis (Meatherall Consulting, Winnipeg, Manitoba, Canada). Fasamo and Finola contained less than 0.06% THC every year of this study, well below Health Canada acceptable THC limit of 0.3%. The effect of N and P on THC content was not considered in the present study. At maturity, plants from all seven rows per plot were cut (Finola: 2000 Sep. 20, 2001 Aug. 30 and 2002 Sep. 16. Fasamo: 2000 Oct. 03, 2001 Sep. 11 and 2002 Sep. 23) near soil level using a single row binder (Suzue), put in cloth bags, and left to dry in the field. The dried plant samples were then weighed for biomass determination, and threshed with a plot combine (Wintersteiger). Plant height was determined near maturity, with a single measurement per plot. Plant density was determined in 2001 and 2002, by counting the number of plants, determined from stubble, in two m 2 quadrants per plot, after harvest. Seed samples were further dried at 40 C for 24 h, cleaned and weighed for seed yield and other determinations. Percent oil content (dry matter basis) was determined with an Oxford 4000 continuouswave low resolution nuclear magnetic resonance (NMR) instrument, according to AOCS methodology (Anonymous, 2000). Percent protein content (dry matter basis) was determined by generic combustion analysis (LECO FP-528) on 0.5-g samples of dried seed (105 C, 16 h) using a nitrogen to protein conversion factor of Statistical Analysis Data were subjected to analysis of variance, and treatment means were separated using least significant difference (LSD) test at the probability level of Combined analysis of experiments across years (fixed effect) was done to determine year interactions (Steel et al. 1997). Analysis was performed using SAS software for personal computers (Cody and Smith 1991). Interactions were plotted and curve fitting, when appropriate, was performed using Excel. RESULTS AND DISCUSSION Plant Density Of the 2 yr that plant density was recorded, 2002 values (35 plants m 2 ) were much lower than those of 2001 (82 plants m 2 ) (Table 2). The low plant density in 2002 was likely due to severe drought that year, as well as the fact that the 2002 experiment was re-seeded in late June, due to the failure of an earlier seeding date. Cultivars differed in plant density only in 2002, with Finola having higher (41%) plant counts than Fasamo. The application of increasing rates of N did not have a detrimental effect on plant density in either year. However, plant density reductions of up to 23% were observed in some N treatments in both 2001 and 2002 when P fertilizer was applied. Nyborg (1961) found that seed-placed N and P commercial fertilizers reduced emergence of several crops, especially when

3 VERA ET AL. FERTILIZER REQUIREMENTS OF INDUSTRIAL HEMP 941 Table 1. Some characteristics of soil used in field experiments, and growing season precipitation Nitrate-N Extractable P in 0 60 cm in 0 15 cm Precipitation (mm) Year z (kg N ha 1 ) (kg P ha 1 ) ph May June July August Average y z Soil was sampled in the spring in 2000, and in the previous autumn in 2001 and y Long-term average ( ) precipitation. Table 2. Hemp responses to cultivar, and N and P fertilizer rate at Melfort, Saskatchewan, Canada in 2000, 2001 and 2002 Plant density z Plant height Biomass Seed yield Seed weight Seed protein Seed oil Analysis of variance (P value) Year (Y) <0.001 <0.001 < <0.001 <0.001 <0.001 Cultivar (C) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Nitrogen rate (N) <0.001 <0.001 < < Phosphorus rate (P) <0.001 < < Y C < <0.001 <0.001 <0.001 Y N <0.001 < Y P < C N < <0.001 C P N P C N P Y C N Y C P Y N P Y C N P CV% Means (plants m 2 ) (cm) (kg ha 1 ) (kg ha 1 ) (mg) (%) (%) Year 2000 ND y LSD Cultivar Fasamo Finola LSD Nitrogen rate (kg ha 1 ) LSD Phosphorus rate (kg ha 1 ) LSD z Plant density was not measured in y ND refers to not determined. the fertilizers were concentrated in a narrow band around the seed. Deleterious effects of seed-placed urea on the emergence of durum wheat (Malhi et al. 2003) and canola (Johnston et al. 2002; Malhi et al. 2003) have also been recently reported. Malhi et al. (2003) concluded that this adverse effect could be mitigated by diluting the fertilizer around the seed, using a wider spreader opener, or by slowing the release of the fertilizer into the soil by coating the fertilizer granules with a urease inhibitor or with polymers. In the present study, the N fertilizer was top-dressed, which likely explains the lack of detrimental effect of increasing rates of N on hemp plant density. The P fertilizer was seed-placed, and this may have affected hemp seed germination in the 2 yr (2001, 2002) in which dry soil conditions were most severe at seeding time (Table 1). This agrees with the findings of Nyborg et al. (1961) who observed that the emergence of flax was more affected by N and P fertilizer, applied in close proximity to the seed, under a low soil moisture regime than at field capacity.

4 942 CANADIAN JOURNAL OF PLANT SCIENCE Plant Height Plant height of both cultivars progressively declined from 2000 to 2002, as conditions became drier (Table 2). Fasamo was consistently and substantially taller (54 58%) than Finola each year. Increasing rates of applied N resulted in increased plant height each year (Fig. 1), but this response, quadratic in nature, was more pronounced in 2000, compared to the dry years of 2001 and The addition of P resulted in plant height increases in 2000 and 2002 (Fig. 1) and, as with N, this effect was also more pronounced in These findings are in agreement with Coffman and Gentner (1977) who observed that applied P fertilizer increased plant height of greenhouse-grown Cannabis plants. Positive responses of plant height to the addition of N and/or P fertilizers have also been reported on wheat (Nielsen and Halvorson 1991; Abedin et al. 1998). These responses usually followed a quadratic pattern. Biomass Biomass production of the two hemp cultivars responded differently to the addition of N each year (Fig. 2). Biomass of both cultivars tended to increase as the levels of N increased, but the taller cultivar, Fasamo, produced more biomass (34%) than Finola in all years and at all levels of N (Table 2). However, the rate of biomass increase as the N rates increased was larger for Fasamo during the wet year of 2000 (Fig. 2). The majority of the responses were of a quadratic nature, as the magnitude of the increase tended to diminish with increasing levels of N. The addition of P fertilizer reduced hemp biomass production in This may have been due to lower plant density that occurred after seed-placed application of P fertilizer. Based on soil test nitrate-n levels in the different years, greater biomass response to applied N was expected in 2002, as compared to 2000, but this did not happen in our study, because of the poor crop growth due to severe drought conditions that prevailed during the growing season of The positive responses of hemp biomass to the addition of N fertilizer in this study agree with the results of studies in eastern Canada (Gehl 1995), which concluded that hemp fibre production was very responsive to N application. Positive response of biomass to applied P fertilizer has been reported on greenhouse-grown Cannabis plants (Coffman and Gentner 1977). In the present study, the negative response of hemp biomass to the addition on P fertilizer in the two dry years (2001, 2002) is associated with reduced plant density observed during these years after the application of P. Seed Yield Cultivars differed in seed yield in all 3 yr of the study (Fig. 3). Finola had a greater seed yield (25%), and suffered lesser reductions in seed production than Fasamo, during the dry years (2001 and 2002). Finola was able to increase its harvest index during the dry years (from 20% in 2000 to 34% in 2001 and 28% in 2002), while the harvest index of Fasamo experienced little change during the dry period (from 15% in 2000 to 17% in 2001 and 14% in 2002). The addition of N fertilizer resulted in a progressive yield increase as the rate of N increased (Fig. 3). The response of seed yield to the application of N was similar from one year to another and followed a quadratic pattern, particularly for Finola, which reached maximum seed yield at 99 kg N ha 1 in 2000 and 102 kg N ha 1 in 2002, and then decreased at the last N rate. Fasamo, on the other hand, did not reach a maximum seed yield value within the range of N rates used in this experiment at any time, but rather increased up to the last N rate (120 kg N ha 1 ) each year. The average amount of nitrate- N in the 0- to 60-cm soil was 40 kg N ha 1 (Table 1). Seed yield kg 1 of N was 9.4, 5.9, 4.5 and 3.7 kg ha 1 for Fasamo, and 10.6, 7.7, 6.0 and 4.5 kg ha 1 for Finola, respectively, at 40, 80, 120 and 160 kg ha 1 of soil plus fertilizer N. The addition of P fertilizer reduced seed yield of hemp (Table 2). However, this negative effect of P was significant only in 2001 and, as with biomass, may have been an indirect result of the lower plant density that occurred with seed-placed P in 2001, as well as in Seed yield increases were expected from applied P in 2000, as soil test extractable P level was low (17 kg P ha 1 ) and the precipitation adequate that year, but this did not take place. The use of fertilizers on nutrient-deficient soils has usually shown beneficial effects on the production of crops. Nyborg et al. (1999) indicated that seed yield of barley and canola increased with increasing nitrate-n in the soil up to 88 and 72 kg N ha 1, respectively, but the magnitude of seed yield increase decreased with increasing N levels in the soil, depicting a traditional quadratic response. Similarly, Malhi et al. (1993) observed that the seed yield of barley rarely responded to added P fertilizer in soils with P levels above 24.6 kg P ha 1. In the present study, nitrate-n soil test levels always fell below 55 kg N ha 1, which may explain the positive response of hemp seed yield to applied N fertilizer. On the other hand, extractable P soil test levels were greater than 35 kg P ha 1 in 2 (2001, 2002) of the 3 yr of the study, which may explain the lack of response of hemp seed yield to the addition of P fertilizer. Instances, where the application of fertilizers has resulted in reduced seed yield, have been linked to the inability of crop plants to compensate for reduced emergence caused by fertilizer phytotoxicity, when applied in close proximity to the seed, especially under dry weather conditions (Johnston et al. 2002). Indirect effects from delayed maturity and enhanced weed competition, associated with thin stands (Johnston et al. 2002), are also possible explanations for negative seed yield response to additional fertilizer. In the present study, the deleterious effect of seed-placed P on the seed yield of hemp was associated with reduced plant stands observed in the high P treatment in the 2 dry years of 2001 and Seed Weight Cultivars differed in seed weight in all 3 yr of the study (Fig. 4), with Finola consistently having heavier seeds (7 19%) than Fasamo. This difference was greater during the drier years of 2001 and 2002 than in 2000, which had a more normal precipitation. Other factors or their interactions affected this parameter only in During this wet year, seed weight of Fasamo

5 VERA ET AL. FERTILIZER REQUIREMENTS OF INDUSTRIAL HEMP 943 Fig. 1. The effect of year and N rate, and year and P rate on the plant height of hemp at Melfort, Saskatchewan, Canada. The error bar represents the LSD 0.05 for the interaction. progressively decreased, while that of Finola increased, as the rate of N increased, reaching maximum at 66 kg N ha 1. In 2000, the addition of P caused an increase in seed weight of both cultivars, although this effect was more pronounced on Finola. Seed Protein Content Cultivars differed in seed protein content in all 3 yr (Fig. 5), with Finola consistently obtaining higher protein values (7 16%) than Fasamo. Seed protein content of both cultivars progressively increased from 2000 to 2002, as dry conditions worsened. Cultivar differences also became more evident during the drier years. Increasing rates of N affected seed protein content in all 3 yr, resulting in a progressive increase of seed protein as the rates of N increased (Fig. 5). This effect followed a quadratic pattern. Except for the Cultivar N rate interaction in 2002, no other interactions were significant at any time. The addition of P did not affect hemp seed protein content in any of the years tested. Seed protein of many crops has been reported to be positively influenced by the addition of N fertilizers (Aulakh and Pasricha 1998; Mason and Brennan 1998; Johnston et al. 2002). Although in the present study the addition of P did not affect the seed protein content of hemp, it is possible that P may indirectly affect seed protein when P becomes the limiting factor for the use of adequate N (Robson and Pitman 1983). Seed Oil Content The two cultivars differed in seed oil content in all 3 yr of the study (Fig. 6), with Finola consistently showing higher seed oil values (6 12%) than Fasamo. Seed oil content tended to decrease as the years became drier. This decrease was particularly evident for Fasamo, especially in Increasing rates of N affected seed oil content of the two cultivars differently (Fig. 6). In 2001 and 2002, Finola increased seed oil content, as the N rates increased, reaching 1 and 3% higher seed oil at the highest N rate, respectively.

6 944 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 2. The effect of the year, cultivar and N rate on the biomass of hemp at Melfort Saskatchewan, Canada. Fig. 3. The effect of the year and cultivar, and cultivar and N rate on the seed yield of hemp at Melfort, Saskatchewan, Canada. The error bar represents the LSD 0.05 for the interaction.

7 VERA ET AL. FERTILIZER REQUIREMENTS OF INDUSTRIAL HEMP 945 Fig. 4. The effect of year and cultivar on the seed weight of hemp at Melfort, Saskatchewan, Canada. The error bar represents the LSD 0.05 for the interaction. Fig. 5. The effect of year and cultivar, and N rate on the seed protein content of hemp at Melfort, Saskatchewan, Canada. The error bar represents the LSD 0.05 for the interaction.

8 946 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 6. The effect of year and cultivar, and cultivar and N rate on the seed oil content of hemp at Melfort, Saskatchewan, Canada. The error bar represents the LSD 0.05 for the interaction. Seed oil content of Fasamo, on the other hand, decreased by 2 3% in 2000 and by 4% in 2002, at the two highest levels of N. The addition of P did not affect hemp seed oil content or interact with any other factor during the years tested. Reduction in seed oil content of canola as a result of increasing N rates has been reported (Mason and Brennan 1998; Jackson 2000). The reverse relationship of seed oil content and seed protein observed by other researchers (Bhatty 1964; Johnston et al. 2002) was evident in the present study only in the way Fasamo responded to increasing rates of N, but not for Finola. Hemp responded well to the addition of N fertilizer, especially in years with adequate rainfall. Taller plants, greater biomass and seed yield, and higher seed protein and oil content (only Finola), were obtained with increasing rates on N. The application of P in the seedrow usually increased plant height, but depressed plant stands, biomass and seed yield. Of the two hemp cultivars tested, Finola consistently showed lower plant height, earlier maturity, heavier seeds, and higher seed yield, seed protein content and seed oil content than Fasamo, even in dry conditions. This makes Finola a cultivar better suited to hemp seed and oil production in the Parkland region of Saskatchewan. The average amount of nitrate-n in the 0- to 60-cm soil was 40 kg N ha 1. Seed yield kg 1 of N was 9.4, 5.9, 4.5 and 3.7 kg ha 1 for Fasamo, and 10.6, 7.7, 6.0 and 4.5 kg ha 1 for Finola, respectively, at 40, 80, 120 and 160 kg ha 1 of soil plus fertilizer N. In summary, hemp gave a significant yield response to applied fertilizers when levels of plant-available nutrients in soil were low and/or the soil moisture conditions were near optimum for plant growth. ACKNOWLEDGEMENTS We gratefully acknowledge the Agriculture and Agri-Food Canada Matching Investment Initiative (MII) for financial assistance. We also recognize Glenn Moskal, Colleen Nielsen, Ken McJuray, Sheldon Stobbs, Dawnne Campbell and Gerald Serblowski for technical support, and Drs. Hugh Beckie and Randy Kutcher for internal review of the manuscript.

9 VERA ET AL. FERTILIZER REQUIREMENTS OF INDUSTRIAL HEMP 947 Abedin, M. J., Saleque, M. A., Panullah, G. M. and Mazid, M. A Evaluation of two concepts of fertilization for wheat in a calcareous soil of Bangladesh. J. Plant Nutr. 9: Anonymous Oil content of oilseeds by nuclear magnetic resonance. In D. Firestone, ed. Official methods and recommended practices of the AOCS. 5th ed. AOCS, Champaign, IL. Aulakh, M. S. and Pasricha, N. S The effect of green manuring and fertilizer N application on enhancing crop productivity in mustard-rice rotation in semi-arid subtropical regions. Eur. J. Agron. 8: Bhatty, R. S Influence of nitrogen fertilization on the yield, protein and oil content of two varieties of rape. Can. J. Plant Sci. 44: Blade, S. F Industrial hemp in Alberta. Alberta Agriculture, Food and Rural Development. New Crop Development Unit, Edmonton, AB. 18 pp. Clarke, R. C Botany of the genus Cannabis. Pages 1 19 in P. Ranalli, ed. Advances in hemp research. Food Products Press, An Imprint of The Haworth Press Inc., New York, NY. Cody, R. P. and Smith, J. K Applied statistics and SAS programming language. 3rd ed. SAS Institute, Inc., Cary, NC. 403 pp. Coffman, C. B. and Gentner, W. A Responses of greenhouse-grown Cannabis sativa L. to nitrogen, phosphorus and potassium. Agron. J. 69: Gehl, D A summary of hemp research in Canada conducted by the Fibre Division of Agriculture Canada Report prepared at the AAFC Research Farm, Indian Head, SK. 10 pp. Hanks, A Canada: hemp industry-in-progress. J. Indust. Hemp 7: Jackson, G. D Effects of nitrogen and sulfur on canola yield and nutrient uptake. Agron. J. 92: Johnston, A. M., Johnson, E. N., Kirkland, K. J. and Stevenson, F. C Nitrogen fertilizer placement for fall and spring seeded Brassica napus canola. Can. J. Plant Sci. 82: Johnston, A. M., Malhi, S. S., Schoenau, J. J. and Exner, S. W Nutrient and biomass accumulation of major crops. Res. Rept. Canadian Fertilizer Institute, Ottawa, ON. Malhi, S. S., Nyborg M., Penny, D. C., Kryzanowski, L., Robertson, J. A. and Walker, D. R Yield response of barley and rapeseed to P fertilizer: Influence of soil P level and method of placement. Commun. Soil Sci. Plant Anal. 24: Malhi, S. S., Oliver, E., Mayerle, G., Kruger, G. and Gill, K. S Improving effectiveness of seedrow-placed urea with urease inhibitor and polymer coating for durum wheat and canola. Commun. Soil Sci. Plant Anal. 34: Mason, M. G. and Brennan, R. F Comparison of growth response and nitrogen uptake by canola and wheat following application of nitrogen fertilizer. J. Plant Nutr. 21: Nielsen, D. C. and Halvorson, A. D Nitrogen fertility influence on water stress and yield of winter wheat. Agron. J. 83: Nyborg, M The effect of fertilizers on emergence of cereal grains, flax and rape. Can. J. Plant Sci. 41: Nyborg, M., Malhi, S. S., Mumey, G., Kryzanowski, L., Penny, D. C. and Laverty, D. H Economics of nitrogen fertilization of barley and rapeseed as influenced by nitrate-nitrogen in soil. Commun. Soil Sci. Plant Anal. 30: Pate, D. W Hemp seed: Valuable food source. Pages in P. Ranalli, ed. Advances in hemp research. Food Products Press, An Imprint of The Haworth Press Inc., New York, NY. Ranalli, P Agronomical and physiological advances in hemp crops. Pages in P. Ranalli, ed. Advances in hemp research. Food Products Press, An Imprint of The Haworth Press Inc., New York, NY. Robson, A. D. and Pitman M. G Interaction between nutrients in higher plants. Pages in A. Lauchli and R. R. Bielski, eds. Encyclopedia of plant physiology. Springer-Verlag, Berlin, Germany. Small, E., Pocock, T. and Cavers, P. B The biology of Canadian weeds Cannabis sativa L. Can. J. Plant Sci. 83: Steel, R. G. D., Torrie, J. H. and Dickey, D. A Principles and procedures of statistics: A biometrical approach. 3rd ed. McGraw-Hill Book Co., New York, NY.

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11 This article has been cited by: 1. K. Tang, P.C. Struik, X. Yin, D. Calzolari, S. Musio, C. Thouminot, M. Bjelková, V. Stramkale, G. Magagnini, S. Amaducci A comprehensive study of planting density and nitrogen fertilization effect on dual-purpose hemp ( Cannabis sativa L.) cultivation. Industrial Crops and Products 107, [Crossref] 2. Enio Campiglia, Emanuele Radicetti, Roberto Mancinelli Plant density and nitrogen fertilization affect agronomic performance of industrial hemp ( Cannabis sativa L.) in Mediterranean environment. Industrial Crops and Products 100, [Crossref] 3.. Literature Cited [Crossref] 4. Li-jun LIU, He-quan CHEN, Xiao-bing DAI, Hui WANG, Ding-xiang PENG Effect of Planting Density and Fertilizer Application on Fiber Yield of Ramie (Boehmeria nivea). Journal of Integrative Agriculture 11:7, [Crossref] 5. Cecil L. Vera, Arthur Hanks Hemp Production in Western Canada. Journal of Industrial Hemp 9:2, [Crossref]