Effect of harvest date on yield and quality of vetch (Vicia villosa, Roth) and triticale (X tritcosecale, Witmack) forage mixtures

Gasmi-Boubaker Aziza*, S Ben Youssef, C Benila and N Rebai

* National Institute of Agronomy, Tunisia, University of Carthage
azizaboubaker@yahoo.com
National Institute of Research Tunisia, University of Carthage

Abstract

The objective of this research was to evaluate the effects of harvest date (156, 181 and 195 days after sowing) and of the different seeding ratios of vetch triticale (100:0,  67:33, 50:50, 40:60, 33:67 and 0:100) on dry matter (DM) yield and quality of triticale and vetch forage mixtures to determine the most appropriate mixture and the optimal harvest date.

The highest DM yield was found to be 11.02 T/ha for pure roughage triticale while the lowest was given by the vetch in three harvest times. The highest contents of crude protein (CP) were obtained in the first harvest date. Vetch monoculture provided the highest CP (22.2% DM), followed by the mixture with seeding ratio 67:33. In contrast, triticale monoculture had the lowest CP. The increase of vetch seeding ratio proportion in mixture increased CP and decreased DM yields. This study shows that in order to produce suitable DM and quality forage, the best choice of seeding ratio is 67:33 and 50:50 vetch triticale to be harvested at early stage of growth (first week of April).

Key words: crude protein, dry matter digestibility, dry matter yield, land equivalent ratio

Introduction

Roughage produced on crop fields is basic source in ruminant nutrition. Since high quality forage optimizes the productivity of the animals, increasing the quality of forage available is one of the best methods of improving overall feeding efficiency.

Triticale is an important forage crop due its high yield and high carbohydrate level, but forage is relatively poor in CP concentration and cannot meet the requirement of ruminants when distributed alone, especially to milking dairy cows which needs large amounts of protein. Vetch herbage is reported to have high crude protein level (16.5 – 26.5%;  Hadjipanayiotou & Economides 2001). Common vetch is popularly grown for fodder, hay or seed production. Feeding vetch is reported to increase milk yields of cows and goats and growth performance of beef cattle (Pinkerton & Pinkerton 2000). However, because of having weak and thin stem, the vetches spread. So harvest gets difficult and because of losing leaves, its forage and quality decrease. Therefore, growing either legumes or cereals in a sole crop is not ideal for forage production.

For forage crops, it is important to produce greater forage yields per hectare and higher nutritional quality (Dura et al 2012). Mixed cropping of cereals with forage legumes can improve both quantity (Mpairwe et al 2003) and quality of fodder over a pure cereal crop (Umuna et al 1997). Vetches are reputed for their beneficial compatibility with cereal crops when they are grown as mixtures. It was reported that mixtures containing 25-50 % legume produced more quality forage and yield per unit area than those of pure sowings (Alemu et al 2007). In the mixtures, triticale provides support for climbing vetch and facilitates mechanical harvesting (Thomson et al 1990).

Meanwhile, to produce suitable dry matter and quality forage, it is essential to know the best mixture of vetch and triticale and the optimum stage for harvest. The objective of this investigation was to evaluate the effect of seeding rate and harvest timing on yield, quality of triticale and vetch mixtures forage and land use efficiency in order to determine the most appropriate mixture and the optimal harvest date. 

Materials and methods

Forage and experimental design

A field experiment was performed during 2010-2011 at the experimental station of INRAT situated in the north of Tunisia (36° 50’ 37" N; 10° 11’ 28" E) under rain fed conditions. The total precipitation from September 2010 to June 2011 was 516 mm. The texture of soil is clay-loam. The experimental structure was a replacement series, consisting of Vetch (Vicia villosa, Roth) and triticale (X tritcosecale,Witmack) in pure stands and different mixtures. At sowing, vetch triticale ratios were: 100:0,  67:33,  50:50,  40:60,  33:67 and 0:100. Seeding rates for the pure stands were 100 viable seeds/m² for  vetch and 200 viable seeds/m² for triticale, while seeding rates for the mixtures were proportional to the pure stand seeding rates. The experiment was arranged in a complete randomized block design with 4 replications. Each plot was 2x2 m with ten rows. Only plots of pure triticale were fertilized at the beginning of the experiment with 50 kg N/ha. The crops were sown on November 1, 2010 and forage samples were collected 156 (7^th April/2011), 181 (2^nd May/2011) and 195 (16^th May 2011) days after sowing.  

Yield and quality measurements

Forage yield was determined by harvesting the crops by hand at ground-level and weighing the fresh material. Samples (5 kg) of green forage were dried in a forced-draught oven to constant weight to determine dry matter (DM) percentage and to calculate DM yields.  A second set of forage samples (1.5 kg) from each plot was dried at 40°C for 72 h and ground to pass a 1 mm screen to estimate crude protein (CP) following Kjeldahl method (AOAC, 1984). Dry matter digestibility (DMD) was determined as described by Michalet-Doreau and Aufrère (1988). Forage samples (0.5 g) were weighed into a 50 ml centrifuge tube in triplicate. Thirty milliliters of 0.1 N HCL containing 0.2 % (w/v) pepsin was added and incubated at 39 °C in a water bath. After 24 hours of incubation, samples were filtered into crucibles and then transferred back to the centrifuge tubes.  The volume in the tube was made up to 30 ml with acetic acid: cellulase buffer (2.5 % (w/v) then incubated in the water bath at 39 °C for 48 hours. At the end of the incubation period, the contents of the tubes were filtered through dried and pre-weighed crucible. The residues were washed with 100 ml of boiling water then oven dried overnight at 105 °C to calculate DMD. 

Calculations and Statistical analyses

The land equivalent ratio (LER) was calculated to measure competition in and advantages of intercropping. LER value was determined by the formula:

LER = (Yvm/Yvp) + (Ytm/Ytp) where Yvp and Ytp are yields of vetch and triticale in pure stands, respectively, and Yvm and Ytm are yields of vetch and triticale in mixtures. The effect of seeding rate and harvest timing on DM yield, CP content, DMD of forage and land use efficiency was evaluated by analysis of variance with the statistical software SPSS for Windows 10.0. The significance level was p<0.05.

Results and discussion

The early cut (April 7th, 2011) corresponded to the ‘booting’ stage in triticale, while the vetch was in first flowers. The second cutting time (May 2th, 2011) corresponded to the ‘anthesis’ stage in triticale and full bloom in vetch. During the third harvest (May 16th, 2011), triticale was in the soft dough stage while 50% of pods reached the maximum size in vetch. 

Dry matter yield

According to Table 1, DM yield of the mixtures of vetch and triticale were not affected (P>0.05) by the harvest timing, but there was significant difference among the roughage mixtures. The highest DM yield was found to be 11.02 T/ha for pure roughage triticale. The high DM yield of triticale has often been reported for different cultivars of triticale sown at different locations and harvested at different stages of growth.  Bilgili et al (2009) indicated that triticale lines can produce more than 16 T DM/ ha in a Mediterranean-type environment. Delogu et al (2002) obtained an average of 13.2 T DM/ ha at the milk-dough stage for nine triticale cultivars grown in Italy. In Spain, Santiveri et al (2004 ) found 16.58 T/ha and 22.89 T/ha DM yields of eight triticale lines at anthesis and maturity, respectively, while in Greece, Lithourgidis et al (2006) reported that the DM yield of triticale was 10.8 T/ha. In contrast, the lowest DM yields were given by the vetch in three harvest times, consistent with the lower productivity of legumes like berseem, clover and common bean. But, DM yields of vetch triticale mixtures exceeded those of pure vetch. Increased yield of vetch in mixture with cereal crop such as oat, barley and wheat has also been reported by other researchers (Thomson et al 1990;  Roberts et al 1989).

Land Equivalent Ratio (LER)

The LER value shows the relative amount of land under pure stands to produce the same yield as the mixture. The mixture is more efficient in terms of land use if the LER value is >1 ((Dhima et al 2007). Erol et al (2009) obtained LRE values of 1.13 and 1.33 for 55:45 and 45:55 oat vetch mixture, respectively. Similarly, Dhima et al (2007) reported yield advantages in terms of total LER for common vetch-wheat mixtures (1.05) at a 55:45 seeding ratio and for common vetch-oat mixtures (1.09) at a 65:35 seeding ratio. In this study, LER ranged from 1.05 to 1.59 for vetch triticale mixtures harvested 156 days after sowing. These mixtures would produce from 5 to 59% more feed than pure vetch. Thus, the advantage of combining vetch with triticale will be recorded at early stage of harvest.

Crude protein (CP) content

Total nitrogen concentration in the forage, expressed as crude protein, is a useful measure of forage quality, since adequate intake of nitrogen is essential for growth and milk production by livestock. Protein is also one of the most costly supplements for livestock, so high protein forages are desirable. Major factors affecting forage quality include: 1) crop species, 2) maturity and 3) environment. It is significant that most researchers agree that protein content of legumes is typically much higher than that of grasses. Seed proportion of intercropping components is also a factor affecting CP content of forage. According to table 3, the highest level of CP was observed in the first harvest with vetch (22.2% CP) and the lowest with triticale (12.8% CP). Crude protein concentration progressively increased (P<0.05) as vetch percentage at sowing. In contrast, the minimum CP content was recorded during the third cut corresponding to the mid May. These results confirm the findings of Caballero et al (1995); Lithourgidis et al (2006) and Dura et al (2012) who reported that CP contents in pure sowing of legumes are higher than in cereals and decline as plants mature from the vegetative stage through the reproductive stages particularly after flowering.  

Dry matter digestibility

Previous research indicates that quality of forage is mostly affected by the plant species and plant maturity. It is well known that digestibility, energy content and protein level of plants are highest when the plants are in the early vegetative growth stage. In this study, the results for DMD (Table 4) showed no effect (P>0.05) of harvest dates or plant species. Dry matter digestibility was similar between vetch and triticale but differed slightly among their mixtures. The average DMD of vetch and triticale in pure sowing was 53.1 and 52.8%, respectively. These results are lower than that reported by several researchers. In early studies, Van Keuren and Underwood (1990) reported that digestibility levels of triticale were 79.6, 66.4 and 61.3% in the boot, milk and dough stage, respectively. In regions with Mediterranean-type climates, the results of studies using a total of 33 triticale lines demonstrated that degradation levels of DM were 59.0%  in whole plant triticale forage (Bilgili et al 2009).

Conclusions

• As many researchers concluded, growing either legumes or cereals in a sole crop is not ideal for relatively high biomass production and quality in terms of feed value for livestock. It seems that the best choice of seeding rates is 67:33 and 50:50 vetch triticale mixtures Also, and as the optimum stage for harvest is often a compromise between quality and quantity, it will be recommended to harvest at early stage of growth (first week of April).

Acknowledgements

This research was financially supported by the “Laboratoire d’économie et technologie alimentaires, INAT’ 

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Received 16 December 2012; Accepted 14 January 2013; Published 5 February 2013

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