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Influence of nitrogen supply and P and K levels of the soil on dry matter and nutrient accumulation of fiber hemp (Cannabis sativa L.)

Ildiko Ivonyi¹ , Zolton Izsoki¹ and Hayo M. G. van der Werf²

¹Agricultural University of Debrecen College of Agricultural Water and Environmental Management, Crop Production Department, P. O. Box 3, H-5541 Szarvas, Hungary

²INRA, Unité d’Agronomie de Rennes-Quimper, ENSAR - 65, rue de Saint-Brieuc, F 35042 Rennes, France

        Ivonyi, Ildiko, Zolton Izsoki and Hayo M. G. van der Werf 1997. Influence of nitrogen supply and P and K levels of the soil on dry matter and nutrient accumulation of fiber hemp (Cannabis sativa L.). Journal of the International Hemp Association 4(1): 82-87. A hemp (Cannabis sativa L.) fertilization experiment was conducted in Szarvas, Hungary, from 1990 to 1992. This paper reports the effect of nitrogen (N) application rate, soil phosphate (P) and soil potassium (K) levels on dry matter and nutrient accumulation. Four levels of N, P and K fertilizer were applied in a split-split plot design. Eleven regimes were selected to examine the development resulting from these treatments during the growing season. From the beginning of June to the beginning of August, the daily increase of above-ground dry matter was 0.17-0.19 t/ha. Intensive accumulation of N and K₂O had begun in mid-May and lasted for a month. By the end of this phase, 79 % of total N uptake and 77% of total K₂O uptake had occurred. The P₂O₅ uptake was constant during the period under examination. During the period of intensive nutrient uptake, the daily N uptake was 3-4 kg/ha and the daily K₂O uptake was 3-6 kg/ha . The P₂O₅ uptake was 0.25-0.64 kg/ha during the period under examination. Nutrient supply influenced dry matter accumulation and the rate of N and K₂O uptake. More importantly, the N supply increased the amount of dry matter formed and the rate of N, P₂O₅ and K₂O increased uptake significantly at all times. At the time of maximum nutrient uptake, the amount of N incorporated into the plant was 142-256 kg/ha, the amount of P₂O₅ incorporated into the plant was 52-67 kg/ha, and the amount of K₂O incorporated into the plant was 223-358 kg/ha, depending on the supply of nutrients. N fertilization increased the stem yield at all P and K supply levels of the soil up to 160 kg/ha N. The specific nutrient uptake for 1 t of above-ground dry matter of fiber hemp was 14.1 kg N; 3.5 kg P₂O₅ and 19.8 kg K₂O.

Introduction
         Fiber hemp (Cannabis sativa L.) is a fast growing annual crop which could potentially be used as a raw material in the areas of textiles, paper products, foods and feeds, and energy applications. This plant has an important agronomic potential in a great range of altitudes, climates and soils (Riddlestone and Desai 1994).
         In Hungary, publications on hemp mainly cover cultivars, breeding, biological, ecological and general practices for the crop (Mándy and Bócsa 1962, Ruzsányi 1967, Bócsa 1968, Horkay 1980). The literature on fertilization is very limited. Csókás (1914) was the first in Hungary to test the dry matter and nitrogen (N), phosphorus (P) and potassium (K) accumulation of fiber hemp. In his experimental work, he found that the maximum above-ground dry matter yield was reached by July 30. The maximum dry matter yield was 14.9 t/ha, with 35 kg/ha N, 59 kg/ha P₂O₅ and 188 kg/ha K₂O fertilization. The maximum N uptake was 139 kg/ha reached by July 4, the maximum P₂O₅ uptake was 36 kg/ha, K₂O uptake was 273 kg/ha both reached at July 30. In Jakobey’s (1970) 3-year experiment, maximum above-ground dry matter yield (including shed plant parts) and maximum N, P₂O₅ and K₂O uptake were reached simultaneously towards the middle or the end of July. At that time, the dry matter yield was 7.3 t/ha, the N uptake was 103 kg/ha, P₂O₅ uptake was 47 kg/ha and the K₂O uptake was 209 kg/ha on a soil containing a moderate level of N, and P and a sufficient level of K. In the 2 weeks after that, the dry matter decreased because of leaf senescence. In the experiments by Csókás (1914) and Jakobey (1970), the formation of 1 t of above-ground hemp dry matter required respectively 9 and 14 kg of N, 2.4 and 6 kg of P₂O₅ and 18 and 28 kg of K₂O.
         According to the literature, the effect of N fertilization on the yield of fiber hemp is larger than the effect of P or K. In the Netherlands, Poland and Italy, N fertilization rates between 150 and 240 kg/ha gave the highest stem yields, whereas the highest bast fiber yields were obtained at N rates between 50 and 150 kg/ha (Aukema and Friedrich 1957, Jaranowska 1964, Rivoria and Marras 1975, Marras and Spanu 1979).
         Fertilization experiments have been conducted on different soil types in Hungary. The effect of N on stem yield was positive up to 240 kg/ha, but above 100-150 kg/ha N, the bast fiber yield and the quality of the fibers decreased (Nagy 1968, Ruzsányi 1970, György 1989). P fertilization alone did not increase stem yield (Nagy 1968). In the experiment of Ruzsányi (1970), P fertilization even decreased stem yield on low phosphorus soils. P is needed for the realization of the N effect, but hemp is able to absorb the small quantity of P it requires from the soil. According to these Hungarian experiments, the best fertilization rates for fiber hemp are: N 80-110 kg/ha, P₂O₅ 0-50 kg/ha, and K₂O 50-200 kg/ha .
         The literature suggests that the main nutrient factors affecting the yield of fiber hemp are N and K. Recent data to be used as a basis for fertilizer recommendation are needed. This data should consider nutrient type and quantity, soil supply, crop rotation and the effect of nutrient supply on yield and plant quality (van der Werf 1991). We evaluated these factors and now report the effects of N, P, K supply (primarily N) on fiber hemp dry matter and N, P, K accumulation, and stem yield.

Table 1. Applied treatments and their influence on the nutrient supply of the soil (Szarvas, 1990-1992)

Table 2. The influence of nutrient supply on highest and specific N, P₂O₅ , and K₂O uptake of fiber hemp (Szarvas, 1990-1992)

Materials and methods
         The experiment was undertaken at Szarvas, in the south-eastern part of Hungary from 1990 to 1992. Soybean was grown prior to the hemp. The soil was a chernozem meadow type which had a calcareous subsoil.
         Four levels of N, P, K fertilizers were applied in a split-split plot, randomized block design, with 64 treatments and three replications to determine the yield. In the P and K treatments, the P₁, K₁ levels were aimed at maintaining a suitable soil nutrient level, whereas the P₂, P₃ and K₂, K₃ were aimed at developing different nutrient levels. The following eleven treatment regimes were selected to examine the course of the dry matter yield, nutrient content and nutrient accumulation of fiber hemp during the growing season: 1. N₀P₀K₀; 2. N₀P₂K₂; 3. N₀P₃K₃; 4. N₁P₀K₀; 5. N₁P₂K₀; 6. N₁P₀K₂; 7. N₁P₂K₂; 8. N₂P₀K₀; 9. N₂P₃K₀; 10. N₂P₀K₃; 11. N₂P₃K₃. The treatments and their connection with the soil nutrient supply are shown in Table 1.
         The fiber hemp variety ‘Kompolti’ was planted in the first week of April, at a seeding rate of 90 kg/ha and a row width of 12 cm. Total above-ground plant samples (shed plant parts -primarily leaves- were not included) were taken every second week, six times during the growing season, on 2 x 1 m of row (2 x 0.12 m 2 ). The distance between two sample areas was at least 2 rows. After the fresh weight of the samples was determined, they were dried in air. Then the moisture content of the air dried material was determined (at 105 C°, dried to constant weight) to allow the calculation of dry matter yield. The N, P and K content of the dry matter was determined by photometer. Sampling took place on the following dates: 15 and 30 May, 18 June, 02, 16 and 30 July in 1990; 30 May, 12 and 28 June, 15 and 30 July, 14 August in 1991; 13 May, 01, 16 and 29 June, 17 and 29 July in 1992.
         At final harvest, we determined stem yield by harvesting the entire 15.75 m 2 net plot area. At the 11 treatment areas where samples had already been taken during the growing season, we corrected for the sample areas. Stem yield is defined as stems + some inflorescences at 10 % moisture, which is the hand-over situation for hemp yield to the textile factory.
         The specific nutrient uptake was determined from the highest nutrient uptake during the growing season and from the highest dry matter yield (total above ground plants: stems + leaves + inflorescences without shed plant parts, at 10 % moisture).
         Chemical plant protection was only used against the flea beetle (Psylliodes attenuata) at emergence.
         In two of the three years, the annual precipitation was less than the average of the previous 75 years (1990: 458 mm, 1991: 586 mm, 1992: 336 mm, and the average for 1901-1975: 538 mm). The best year was 1991, when rainfall was above average, but accumulated temperature and sunshine were below average.
         The results were evaluated by analysis of variance according to Sváb (1981).

Figure 1. Dry matter accumulation of fiber hemp (1990-1992, Szarvas)

Figure 2. Influence of N supply and P and K level of the soil on dry matter accumulation of fiber hemp (1990-1992, Szarvas)

Figure 3. Effect of N fertilization and K level of the soil on N uptake of fiber hemp (1990-1992, Szarvas)

Dry matter accumulation
         The three-year average dry matter yield was 14.1 t/ha, the highest was 15.0 t/ha in a wet year (Fig. 1).
        Dry matter accumulation happened at a slow rate in the first two months of the growing season. Twenty nine percent of the total weight had accumulated by the end of May and the middle of June. Rapid growth followed for two months to the beginning of August. During this period, the daily increase of dry matter was 0.17-0.19 t/ha.
         The typical accumulation curve has two peaks, which happened in the two better years, 1990 and 1991. This has been previously observed by Bredemann (1945) and by Mándy and Bócsa (1965). This phenomenon may be connected with the female plants’ energetic development during and after male flowering. In the dry year 1992, accumulation curves were continuous.
         The dry matter accumulation was 20-58 % higher for N₁ and N₂ than the control at all sampling dates (Fig. 2). NPK fertilization (N₂P₃K₃) resulted in 11-79 % higher curves than in the control plots. There were no significant differences between N₁ and N₂ treatments during the growing season. In the case of the last harvest, there was no effect of P and K fertilization.

N, P₂O₅ and K₂O uptake
         On average, the maximum N uptake was 210 kg/ha by the 15-29 July sampling date (Fig 3). N₁ and N₂ fertilization resulted in a longer N uptake season and a significant increase in the incorporation of N compared to the control. The maximum N uptake for N₁ was 219 kg/ha and for N₂ it was 255 kg/ha. These differences were statistically significant.
         The rate of P₂O₅ uptake was largely constant during the growing season (Fig. 4). On average, the maximum of P₂O₅ uptake was 58 kg/ha at the last sampling date. The time of maximum P uptake was earlier with the N₂P₃K₃ treatment. The maximum P uptake was 66 kg/ha at N₂P₀K₀. This was significantly higher than the control.

Figure 4. Effect of N fertilization and P and K level of the soil on P uptake of fiber hemp (1990-1992, Szarvas)

Figure 5. Effect of N fertilization and P and K level of the soil on K uptake of fiber hemp (1990-1992, Szarvas)

Figure 6. Effect of N supply and P level of the soil on stem yield of fiber hemp (1990-1992, Szarvas)

Figure 7. Effect of N supply and K level of the soil on stem yield of fiber hemp (1990-1992, Szarvas)

        On average, the maximum K uptake was 294 kg/ha on 15-29 July (Fig. 5). N₁ and N₂ resulted in a significant increase of K incorporation compared to the control. The maximum K uptake was 337 kg/ha at the N₂P₃K₃ level, significantly higher than for the other treatments.

Specific nutrient uptake
         Specific N uptake varied from 11.8-17.3 kg/t depending on the treatment (Tab. 2). For the highest dry matter yield, the N requirement for 1 t of dry matter was 14.1 kg for the N₁P₀K₂ treatment. Our results are similar to the earlier results of Jakobey (1970). For the production of one t of dry matter, the P₂O₅ requirement varied from 3.5-5.1 kg and the K₂O requirement varied from 18.6-24.9 kg. Among the eleven selected treatments, the P₂O₅ and K₂O requirements for 1 t of dry matter were smallest at the highest dry matter yield, which was obtained from the N₁P₀K₂ treatment (Tab. 2). For our control treatment (N₀P₀K₀), the specific P₂O₅ and K₂O requirements were similar to those obtained by Jakobey (1970), but with a more balanced fertilization, the specific P₂O₅ and K₂O requirements decreased.

The effects of N fertilization at different soil P levels
         As shown in Figure 6, N fertilization resulted in a significant increase of stem yield at all P levels of the soil as compared to the control. At P₁ and P₃ , 80 kg/ha and 160 kg/ha of N, respectively, caused significant increases in stem yield, but a further increase in the amount of N had no significant effect.
         The P supply of the soil with no P fertilization in the 3 years of the experiment was between 125-134 ppm AL-P₂O₅. This P supply level is considered sufficient on chernozem meadow soil for fiber hemp, because with the annual application of 100 kg/ha P₂O₅ (P₁) - which preserves the supply level - an 1-2 t/ha increase in stem yield can be achieved. At higher P levels, the stem yield did not increase significantly. Our results support the findings of Nagy (1968) and Ruzsányi (1970).

The effects of N fertilization at different soil K levels
         K fertilization resulted in a significant stem yield increase up to the K₁ or K₂ level, as shown in Figure 7.
         N fertilization resulted in a consistent increase in yield at all K levels compared to the control. The highest increase was found at the K₁ and K₂ levels. K supply of the soil (without K fertilization) was between 240-300 ppm AL-K₂O in the experimental years. This K supply level is considered moderate on chernozem meadow soil for fiber hemp, because with K fertilization at a better (K₁-K₂) supply level (350-360 ppm AL-K₂O), a 1-3 t/ha surplus can be achieved.

Discussion
         Maximum above-ground dry matter yield is achieved in the beginning and middle of August in Hungary. In the experimental situation, the dry matter yields were 14-15 t/ha on average, but they were about 10 t/ha without any fertilization. Yield increases (4.2-4.5 t/ha ) were achieved at 80 and 160 kg/ha N.
         Maximum N and K uptake was reached at 15-29 of July. The P uptake continued until August.
         Over the averaged three years, among the 11 designated treatments, the N₁P₀K₂ treatment (80 kg/ha N on a soil with 129 ppm AL-P₂O₅ phosphate and 365 ppm AL-K₂O potassium content) resulted in the maximum dry matter yield: 16.4 t/ha. Thus, according to our findings, the specific nutrient uptake for 1 t fiber hemp dry matter was 14.1 kg N; 3.5 kg P₂O₅ and 19.8 kg K₂O.
         Among all the (64) treatments that they made it possible to examine every combination of N-, P-, K- effects, the N fertilization increased the stem yield at all P and K levels until 160 kg/ha N. The highest stem yield was 18.0 t/ha with 160 kg/ha N at a 129 ppm AL-P₂O₅ and 365 ppm K₂O soil supply level.
         On chernozem meadow soil with a moderate humus layer, 130-200 ppm AL-P₂O₅ and 350-360 ppm K₂O are adequate with 80-160 kg/ha N fertilization.

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