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Crop yield and quality parameters of four annual fibre

crops (hemp, kenaf, maize and sorghum) in the North of


S. Amaducci


*, M.T. Amaducci


, R. Benati


, G. Venturi


aDipartimento di Agronomia,Uni6ersita` di Bologna,6ia Filippo Re6,40126Bologna,Italy bIstituto di Agronomia,Uni6ersita` di Milano,Milano,Italy

Accepted 8 October 1999


Four fibre crops (hemp, kenaf, maize and sorghum) considered amongst the most suitable for the conditions of Northern Italy were compared in 1995 and 1997, over two irrigation regimes (rainfed conditions and restoration of 100% ETp) and in two locations (Bologna and Milano). Three harvests were carried out on each crop at different development stages. At each harvest time data on yield and yield components were collected. Sub-samples of stems of each crop and at each harvest time were analysed following the Van Soest method. On average, fibre sorghum proved to be the higher yielding crop. It produced 26.2 Mg ha−1 of total dry matter of which 18.1 Mg ha−1 was

partitioned to the stems. Fibre maize produced more total dry matter than kenaf (19.0 Mg – 15.7 Mg ha−1) but dry

matter accumulated to stems was higher in kenaf (10.8 and 13.4 Mg ha−1). On average, fibre hemp yielded 14.0 Mg

ha−1of total dry matter and 10.9 Mg ha−1of stems. This result was highly affected by the low hemp production

in Bologna in 1995, where unfavourable conditions, in the first phases of cultivation, resulted in a stunted establishment of the crop (18.7 Mg ha−1of total dry matter in Milano and only 8.3 Mg ha−1of total dry matter

in Bologna). On all crops, irrigation produced a slight increase in total biomass (7%) and in stem dry matter (9%) compared to the rainfed condition. In both locations, yield increase due to irrigation was larger in maize and kenaf, than in hemp while, in 1995, it caused a severe lodging on sorghum. The four species proved to be different for growth rates, patterns of development and particularly for cellulose, hemicellulose and lignin content of stems. Cellulose content varied between 56 – 66% of stem dry matter in hemp, 46 – 57% in kenaf, 35 – 45% in maize and 39 – 47% in sorghum. As harvest time was delayed, cellulose content tended to increase for hemp and kenaf while it decrease for sorghum and maize. Hemicellulose content of hemp and kenaf stems varied between 16 – 19%, while it varied between 26 – 29% in sorghum and maize. Hemicellulose content decreased with irrigation and with delay in harvest time. Lignin content in hemp stem ranged between 8 and 13%, it was 6.9% in kenaf and maize, and ca 8% in sorghum. © 2000 Elsevier Science B.V. All rights reserved.

Keywords:Fibre crops; Fibre quality; Irrigation; Hemp; Maize; Sorghum; Kenaf

* Corresponding author. Tel.: +39-051-2091534; fax: +39-051-2091545. E-mail (S. Amaducci)


1. Introduction

Since the new course of EU agricultural policy, including the increasing interest for renewable raw materials and the political engagement to control CO2emission (Agenda 2000), biomass crops have been studied intensively in the last years. In Italy, in the context of the PRisCA Project (Progamma di Ricerca sulle Colture non-Alimentari), \20 species, potentially fibre or cellulose crops, have been investigated under different conditions dur-ing a period of 5 years.

Among these, hemp, kenaf, sorghum and maize are considered to be the most promising for the conditions of Northern Italy (Amaducci et al., 1998).

Hemp was traditionally grown on large surfaces in the North of Italy, mainly for the textile indus-try and for the production of ropes. Recent stud-ies show that hemp stem could be used to produce paper pulps, geotextile, non-woven material, boards (De Meijer, 1994; Venturi and Amaducci, 1999).

Kenaf has been extensively studied in different Italian conditions (Benati et al., 1990; Di Candilo et al., 1992; Gherbin et al., 1994; Petrini et al., 1994; Amaducci et al., 1998; Venturi and Amaducci, 1999), mainly for its use in the paper pulp industry. Sorghum and maize genotypes characterised by stalk storage organs with high fibre content are among the highest yielding crops for many Italian environments, but received little attention as biomass crops so far.

In 1995 and 1997, hemp, kenaf, fibre sorghum and fibre maize were compared in two location of the Po valley and over two irrigation regimes to evaluate biometrics, potential yields and chemical characteristics.

2. Materials and methods

Field trials were carried out at the experimental stations of the Department of Agronomy of Bologna (Cadriano, latitude 44°3%, longitude 11°2% east, altitude 33 m) and of the Institute of Agron-omy of Milano (Landriano, latitude 45°2%,

longi-tude 9°2% east, altitude 88 m), in 1995 and 1997. Four fibre crops, hemp (Cannabis sati6a, L. cv Futura 77), kenaf (Hibiscus cannabinus, cv Tain-ung 2), maize (Zea mais, cv P 94-102) and sor-ghum (Sorghum bicolor, cv H132) were compared over two irrigation regimes. In particular, a rain-fed control was compared to irrigated crops. Irri-gation schedule was based on periodic restoration, through perforated sleeves, of 100% of potential evapotranspiration (calculated with PAN evapo-ration data) after accounting for rainfall. Restora-tion occurred as soon as 50 mm of ETP was reached, well before any symptims of water stress could occur.

In both tears, a split plot design with four replications was laid down. The species were in the main plots and the irrigation regimes in the subplots. Single plot surface measures 60 m2; a stripe of grain sorghum, 2.5 m large, was sown around each plot to prevent interspecies competition.

According to the growing technique tradition-ally employed (Amaducci et al., 1998) sowing took place at times and with methodologies differ-ent for each crop. Phosphate fertilizing was the same for all species, whilst nitrogen fertilizing was differentiated : 100 kg ha−1

to both hemp and Kenaf, 150 kg ha−1 to the two graminaceous crops.

In 1995, each crop was harvested on three successive dates (24 August, 22 September, and 17 October), the first being considering optimal for hemp, the second optimal for sorghum and maize and the third for kenaf.

In 1997, each crop was harvested only once (hemp on the 29 – 22 August, kenaf on the 7 – 24 October and mais and sorghum on the 27 – 28 August, respectively in Bologna and Mi-lano).


Table 1

Soil analysis in different sites and years


3. Results and discussion

3.1. Comparison of 1995and 1997

The combination of the two locations and the two years of experiments offered a wide range of meteorological conditions. The least rainy condi-tion was registered in Bologna 1997, whilst the most rainy one was always Bologna in 1995 (Ta-bles 1 and 2). In Milano, the total amount of rainfall registered in the two years was similar, however their distribution during the growing sea-son was quite different. In 1995 precipitation were concentrated at the onset and at the end of the growing season (irrigation was necessary in sum-mer). In 1997 rainfalls were abundant and persis-tent in the central part of the growing season. In 1997, irrigation was never necessary and, on the contrary, poor drainage caused a stunted growth and low yields.

The average yield of Milano 1997 was the least realised in the experiment, while, in the other conditions (rainfed and irrigated), the productiv-ity of both environments was not different (Table 3).On average, irrigation produced a slight in-crease in total biomass (7%) and in stem dry matter (9%) compared to the rainfed condition.

The significance of the interaction of fourth order (year×location×irrigation regime× spe-cies) did show that kenaf and maize were the only species on which irrigation increased yield signifi-cantly in one of the experimental situations. In Table 2

Rainfall and irrigation (mm) in different sites and yearsa


aThe first figure indicates rainfall, the sencond one water

supplied with irrigation

Data concerning the optimal harvest of 1995 and data of 1997 were combined and subjected to analysis of variance. Yield and yield components determined in 1995 over the three harvest times were analysed separately and subjected to ANOVA.

Table 3

Total dry matter (t ha−1).


Bologna Milanoc Rainfed Meane

1995 1997 1995 1997

8.3 18.1 18.7

Hemp 11.0 13.4 14.6 14.0

16.3 14.4

Kenaf 17.6 15.6 13.4 17.0 15.7

12.8 18.3

19.7 22.1


Maize 19.7 19.0

Sorghum 29.8 29.4 25.2 20.6 26.1 26.3 26.2


aLSD 5% years×location: 1.76. bLSD 5% irrigation treatment: 0.76.

cLSD 5% year×location×species: 2.81, 2.67 when comparing means with the same level of year and place. dLSD, 5% species: 1.3.


Table 4

Stem dry matter (t ha−1)

Milanoc Rainfed Irrigatedd

Bologna Meane

1997 1995 1997



Hemp 15.2 13.9 8.9 10.3 11.4 10.9

14.5 14.6 11.7

12.9 12.3

Kenaf 14.6 13.4

11.7 12.0 6.3

Maize 13.0 10.1 11.5 10.8

20.1 16.6 13.2

22.3 18.1

Sorghum 18.0 18.1

15.4 14.3 10.0 12.7

Totala,b 13.4 13.9 13.3

cLSD 5% year×location×species: 2.44, 2.39 when comparing means with the same level of year and place. aLSD 5% years×location: 1.43.

bLSD 5% irrigation treatment: 0.63. dLSD, 5% species: 1.19.

eLSD 5% species×irrigation treatment: 1.47, 1.26 when comparing means with the same level of species.

1997 in Bologna, kenaf in well watered conditions produced 17.7 t ha−1 of stem dry matter, whilst in rainfed condition the production was reduced by 36% (11.3 t ha−1). A similar result was previ-ously found in the same environment (Mambelli and Grandi, 1995) when kenaf production was limited by 222 mm of rainfall. Under the other experimental conditions, total and stem dry mat-ter yield of kenaf were consistent with those found in comparable environments (Venturi et al., 1990; Petrini et al., 1994) or in drier and southern conditions (Higgins and White, 1970; Ching et al., 1993; Webber, 1993; Gherbin et al., 1994).

In 1995 in Milano, maize under rainfed condi-tions produced 9.8 t ha−1of stem dry matter and 14.2 t ha−1 with irrigation.

Hemp performance was never affected by water availability. Therefore the crop confirms its good yielding capacity with volumes of water ranging from 200 to 300 m3 ha−1 (Rivoira and Marras, 1976).

In Milano 1995, sorghum yield was decreased by irrigation, which favoured a severe lodging in the crop. In the rest of the situations, the rainfed crop was not different from the watered one.

Over all the experimental conditions, sorghum proved to be the highest yielding crop, either in total biomass (26.2 t ha−1) or in stem biomass (18.1 t ha−1) (Tables 3 and 4). Comparable yield performance has already been found in the same environment in dry conditions (Amaducci et al., 1998; Dolciotti et al., 1998).

Hemp and kenaf did show comparable results. In 1995, when low emergence and slow crop establishment affected hemp yield, cellulose and hemicellulose production were very similar be-tween the two species as a consequence of the higher cellulose content of hemp stems.

Average biomass production of kenaf was 15.7 t ha−1, of which almost 85% was formed by stems. Due to the large proportion of stem in total dry matter, kenaf performed second for this yield component after sorghum.

Considering total dry matter production, maize was the second best crop after sorghum. However, due to the large proportion of leaves (43%), stem production was the lowest recorded in the experi-ment (10.8 t ha−1), thus not statistically different from hemp (10.9 t ha−1).

Hemp scored worst on the average of all exper-imental factors. It should be noted, however, that hemp production in Italy 1995 was extremely low as a consequence of poor emergence and stunted growth in the first phase of the cycle. This circum-stance is pointed out by the interaction year× lo-cation×species, which was highly significant to the ANOVA mainly for the poor performance of hemp in Bologna 1995. (Tables 3 and 4).

3.2. Comparison of three har6est times in 1995


particu-lar, stem production of hemp in Bologna was three times lower than in Milano, where hemp was the highest yielding crop (Table 5).

On average of all situations, irrigation allowed for a slight increase in stem dry matter production (14%) (Table 5). However, only kenaf and maize increased significantly their production (respec-tively, by 38% and 30%) when the irrigation was provided, whilst sorghum seemed to suffer from an excess of water (stem yield decreased by 8%). In Bologna, where the natural precipitation was abundant and above the average, irrigation did not significantly increase stem yield. On the con-trary, in Milano irrigation increased the average production by 19% (Table 6).

At both sites, stem dry matter changed through time, but with a different pattern for each crop (Table 5). While hemp showed a slight, and not statistically significant, decrease in stem yield, sor-ghum, maize and kenaf had a sharp increase in stem dry matter between the first and the second

harvest (respectively, of 83, 82 and 77%). In hemp, the slight decrease in stem production through time, though not statistically significant, was probably due to the loss of small plant, which has been reported to increase with crop senes-cence (Van der Werf et al., 1994; Amaducci, 1998).

Percentage of dry matter of the whole plant was also influenced by harvest time (Table 7). In ke-naf, maize and sorghum the dry matter content increased significantly between the first and the second harvest and only slightly between the sec-ond and the third. In hemp, which was the drier crop, plant dry matter content increased continu-ously through time.

Percentage of lignin, hemicellulose and cellulose on stem dry matter are reported in Table 8. Though variable and not subjected to statistical analysis, the result of the cell wall analysis might allow for some general consideration.

Table 5

Stem dry matter (t ha−1) registered in 1995

Bologna Milanoa Rainfed Irrigatedb H I H II H IIIc Meand

6.5 19.2 12.3

Hemp 13.5 13.3 13.1 12.2 12.9

12.1 10.2

13.2 11.0

Kenaf 14.1 7.9 14.0 14.4


Maize 11.3 14.7 11.3 8.1 14.8 16.2 13.0

17.5 19.5 18.0 12.3 22.5 21.3 18.7

Sorghum 19.9

12.2 13.3 15.1 10.4 16.1 16.0 14.2

Total 16.2

aLSD 5% species×location: 2.77, 2.98 when comparing means with the same level of place.

bLSD 5% species×Irrigation treatment: 2.34, 1.60 when comparing means with the same level species. cLSD 5% species×harvest time (H): 2.71, 2.20 when comparing means with the same level species. dLSD, 5% species: 2.11.

Table 6

Stem dry matter and average dry matter content of total biomass in 1995

Bologna Milanoa Bologna Milano

Rainfed Irrigated Rainfed Irrigated H I H II H III H I H II H III

17.5 14.8

12.6 14.7 15.0 13.9 17.5 17.0

11.8 6.9

Stem Dry Matter (t ha−1)b

Total Dry Matter (%)c 21.8 28.6 28.1 21.7 26.7 30.7


Table 7

Dry matter content of total biomass (%) in 1995

Milanoa H I

Bologna H II H IIIb Meanc

37.8 30.7

Hemp 35.5 37.6 41.7 36.6

17.2 13.9

Kenaf 17.1 18.0 19.6 17.2

23.8 20.5 26.2

24.8 26.3

Maize 24.3

26.6 22.0 28.7 30.1

Sorghum 27.2 26.9

26.4 21.8 27.6 29.4

26.2 26.3


aLSD, 5% species×location: 1.81, 1.62 when comparing means with the same level of place. bLSD, 5% species×harvest time: 1.78, 1.73 when comparing means with the same level of species. cLSD 5% species: 1.15.

Table 8

Cell wall components expressed as a percentage of stem dry matter (1995)

Milano Mean

Sorghum 8.4 8.4 8.0


17.0 15.8 19.6 17.2 16.7 17.2 17.1 17.2

Hemp 17.8

18.0 18.6 19.5 18.5

19.7 15.9

Kenaf 18.8 17.9 18.4

27.7 29.3 27.7 26.0

Maize 27.4 26.0 28.3 26.4 27.4

26.0 26.1 26.2 25.4 25.8

26.7 26.7

Sorghum 25.4 26.0


60.6 66.8 61.1 64.8

56.5 65.6

Hemp 61.8 63.5 62.6

51.7 54.9 56.7

Kenaf 45.6 54.0 56.2 51.2 55.2 53.2

35.6 34.5 45.1 38.4

36.8 37.4

Maize 37.2 38.7 38.0

40.9 39.1 47.2

Sorghum 41.6 43.9 41.4 41.9 42.9 42.4

Lignin appeared to be the component more difficult to predict. Throughout time, it decreased in hemp and it increased in kenaf in both loca-tions; it decreased slightly in sorghum in Bologna and in maize in Milano, while it was constant in the other circumstances.

The apparent decrease in lignin content through harvest time contradicts to previous findings (data not published). This could be explained either by the variability of the crop or by the loss of small and dead plants (therefore lignified), which oc-curred in the last harvests. In general, cell wall analysis provided results in accordance with previ-ous research (Bosia, 1976; Bedetti and Ciaralli, 1976; Van der Werf et al., 1994).

Hemicellulose and cellulose content had a simi-lar trend for the two dicotiledonous crops and a different one for the monocotiledonous. In hemp and kenaf, the content of hemicellulose seemed to decrease over time, while cellulose increased. In sorghum and maize, percentage of cellulose on stem dry matter decrease through time, more evi-dently in Milano, while hemicellulose content was approximately constant.


The value of stem dry matter yield, which were not statistically different among harvest times (Table 5), were averaged for each species and multiplied for the relative content of lignin, hemi-cellulose and hemi-cellulose, and results were plotted in Fig. 1.

According to this calculation, hemp and kenaf show very similar result for all the three cell wall components considered, producing up to 8 t ha−1 of cellulose. Sorghum is the highest yielding crop producing \9 t ha−1 of cellulose, 5.6 t ha−1 of hemicellulose and 1.8 t ha−1

of lignin. Maize had the lowest cellulose production (5.9 t ha−1

), while lignin was similar for hemp and kenaf (1.3 t ha−1) and hemicellulose intermediate between sorghum and the two dicotiledonous crops (4.0 t ha−1).

4. Conclusions

Sorghum was the highest yielding crop in all the test conditions, producing an average of 18.1 t ha−1 of stem dry matter in two years and two locations and, in 1995, 9.4 t ha−1of cellulose and 5.6 t ha−1 of hemicellulose. Sorghum seems preferable to maize, which is less productive and partitions \40% of total dry matter into leaves.

At final harvest, water content of the biomass was still very high in kenaf (82.8%); this might

represent a disadvantage for kenaf since cost of drying and transportation would be higher com-pared to hemp, which is much drier at the end of the cropping season (36.3% of total dry matter).

Hemp reaches its maximum yield between the end of August and the beginning of September, while kenaf should be harvested one month later to achieve maximum yield, therefore time for labouring the heavy soils of the region is shorter with kenaf. Kenaf can be sown at the end of April, while hemp, which is sown with one month of advance, covers the soil earlier in a period when abundant rainfall might cause nutrient leaching and erosion.

Kenaf and maize confirmed to have a higher water requirement compared to hemp and sorghum.


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Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

Table 6

Table 6

Table 7

Table 7

Table 8

Table 8

Fig. 1. Cell wall component yield in 1995.
Fig. 1. Cell wall component yield in 1995. p.7


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