The effect of cutting interval on foliage yield and chemical composition of Tropical Kudzu (Pueraria phaseoloides) cultivated as cover-crop in rubber plantation

Nguyen Van Hiep, Hans Wiktorsson* and Ngo Van Man

 Facultry of Animal Science and Veterinary Medicine, Nong Lam University, Ho Chi Minh City, Vietnam
nguyenvanhiep5@yahoo.com
* Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences,
PO Box 7024, S-750 07 Uppsala, Sweden

Abstract

An experiment was carried out with Tropical Kudzu, which was cover crop for rubber at second year, to evaluate effect of cutting interval on yield and chemical composition of foliage. Four cutting intervals of Kudzu foliage: 40, 50, 60 and 70 days were arranged in a randomized completely block design (RCBD) with 4 replicates in 12 m² of one experimental plot.  

The present study showed decreasing leaf proportion, CP content and increasing DM and ADF content with increasing length of cutting interval. The leaf proportion and CP content ranged from 58.63 to 48.97% and 22.11 to 19.65%, respectively. The DM and ADF content ascended from 21.8 to 26.17% and from 38.01 to 39.94%, respectively. The DM and OM yield of Kudzu foliage were highest at 60-day cutting interval with 5.81 and 5.46 tonnes/ha/6months, respectively. The DM and OM yield at 40-day cutting interval were significantly lower than that at 60-day cutting interval. The fresh and CP yield of Kudzu were 21.75 – 23.13 tonnes/ha/6months and 1.08 – 1.14 tonnes/ha/6months, respectively. There were no significant differences of fresh forage and CP yield among the cutting intervals. 

To provide a balance between quality and yield of Kudzu foliage, the optimum cutting interval was  60 days.

Key words: Biomass, dry matter, leaf-stem ratio, protein, yield

Introduction

Legumes have been considered as suitable crops in intercropping systems with perennial trees. Legume crops are used with the aim of improving soil fertility through root nitrogen fixation and mulching of crop residues (Ashokan et al 1985). Binh et al (1997) and Dung et al (2003) reported that intercropping with leguminous trees can improve soil fertility.

 Tropical Kudzu (Pueraria phaseoloides) is a leguminous plant that appears naturally throughout humid-tropics. It is used as a part of a mixture or a sole cover-crop to prevent soil erosion as well as enrich the soil of tree crops such as coconuts, oil-palm and rubber throughout South East Asia and the Pacific islands. The most important role of Kudzu cover-crop is the beneficial contribution to the parent tree crops through the deposition of leaf litter and nitrogen fixation in the soil (Soong and Yap 1976; Tajuddin et al 1990).

The report of Dongnai Rubber Company (DARUCO 2005) showed that biomass production of Kudzu in the rainy seasons was 36.7, 57.1 and 39.2 fresh matter tonnes/ha at first, second and third years, respectively. Only one cutting per year at the end of the rainy season has been applied in the rubber companies in the region. The whole biomass of the cover-crops has been used as green manure to the rubber field. There is not any demonstration in using this product as animal feed.  

Up to the present time, there are some reports on the production potential of Kudzu foliage for animals by pure planting or grass mixture (Nghia 1978; Quang 1979; Trong 1981; Manh et al 2003) but none  have focused on the nutritional value of Kudzu foliage cultivated as cover-crop in the rubber plantations in Vietnam.

The objective of the study was: 

To evaluate the effect of cutting interval on biomass yield and chemical composition of Tropical Kudzu foliage, which has been inter-planted in the rubber plantation in the second planting year.
 

Materials and methods

Location and climate of the experimental site

The experiment was conducted from July 2006 to January 2007 at the Long Thanh rubber plantation, Dongnai province, Vietnam. It is about 70 km Northeast of Ho Chi Minh city. The weather conditions at the experimental site are characterized by a tropical monsoon climate with two seasons, rainy and dry. The rainy season lasted from April to October, with peaks in May and August and an annual precipitation of about 1700 mm. The monthly mean temperatures ranged form about 23.9 to 34.2 ⁰C with minima in December and maxima during the early rainy season (Figure 1). Air humidity varies in the range 69-83%.

The soil was basaltic red with the following characteristic with Kudzu as cover crop but without frequent cutting: pH_H2O = 4.6; OM % = 3.58; N_total % = 0.205; P₂O₅ % = 0.309; K₂O % = 0.022 (Table 1).

Experimental design and treatments

Tropical Kudzu was planted as cover-crop between rubber rows in the second planting year. Rubber trees have been planted in a spacing of 3 m in the rows and 6 m between rows. Four cutting intervals of Kudzu foliage: 40, 50, 60 and 70-day were arranged in a randomized completely block design (RCBD) with 4 replicates in 12 m² plot (3 m x 4 m). Between the rubber rows, the blocks were made with 3 m width, and in the blocks, plots of 4 m length and 1 m border. The experiment was set up in area of 21 m x 24 m = 504 m².   

Sampling and measurement

The first cutting was done on August 29^th, 2006 in all projected experimental plots to test the balance of biomass production in order to select the experimental plots for laying out the experiment statistically. From then onwards the plots were harvested according to cutting intervals of 40, 50, 60 and 70-day. A total of 3, 2, 2 and 2 cutting times were carried out during the growing season for cutting intervals of 40, 50, 60 and 70-day, respectively. The fresh foliage was cut at 15-20 cm above ground. The Kudzu samples from 12 m² (3 m x 4 m) in each plot were cut by sickle. The fresh foliage was weighed and samples were taken for drying to measure dry matter and used it to the chemical analysis. Soil samples were collected in each treatment after last cutting and in the plots outside of the experiment (in non cutting plot and in non cover-crop plot) for evaluating the effect of the study to the soil characteristics.

Chemical analysis

Chemical composition of foliage: DM, ash, CP, ADF, lignin were analysed in the laboratory of Animal Nutrition Department of Nong Lam University. DM, ash and CP were determined according to AOAC (1990). ADF and lignin were determined by the method of Van Soest et al (1991). Soil characteristics: pH_H20, OM, nitrogen, phosphorus and potassium were analysed in the laboratory of Research Centre for Environmental Technology and Natural Resource Management of Nong Lam University. pH_H20, OM, nitrogen, phosphorus and potassium were determined according to AOAC (1990).

Statistical analysis

The data were subjected to an analysis of variance (ANOVA) by using the General Linear Model (GLM) procedure of Minitab software version 13. When the F test was significant (P<0.05), Tukey’s test for paired comparisons was used (Minitab 13).
 

Results

Effect of cutting interval on leaf dry weight proportion and proximate chemical composition of Kudzu

The leaf dry weight proportions of Kudzu decreased as length of increased cutting interval. The cutting of 70-day interval had the lowest leaf proportion which was significantly different from the treatments 40 and 50-day cutting interval (Table 2 and Figure 2).

The DM percentage of Kudzu foliage increased significantly with increased cutting interval (P<0.001), but the difference was not found significant between the treatment 60 and 70-day cutting intervals. The OM, ADF content of Kudzu foliage increased slightly as length of cutting interval increased but the significant difference was between the treatment 70-day cutting interval with the treatments 40 and 50-day cutting interval. The ash content decreased with the increased cutting interval, as shown in Table 2.

 

Foliage harvested in 40, 50, 60 and 70-day cutting intervals had a CP percentage of 22.1, 20.73, 19.65 and 19.86% of DM, respectively. The significantly higher value was found at 40-day cutting interval compared to other cutting intervals (P<0.01). There was no significant difference in the lignin percentage among treatments and the lignin percentage of Kudzu foliage ranged from 8.93 – 9.02 % of DM.

Effect of cutting interval on foliage production of Kudzu

Effects of cutting interval on the yield of fresh, DM, OM, CP and ADF of Kudzu foliage are presented in Table 3 and Figure 3.

The fresh, DM and OM yield of Kudzu foliage reached peak at 60-day cutting interval and then declined slightly at 70-day cutting interval. The fresh yield of Kudzu foliage varied between 23.13 to 21.75 tonnes/ha/6months, and with non-significant differences among cutting intervals. DM foliage yield harvested with 40, 50, 60 and 70-day cutting intervals was 4.84, 5.25, 5.81 and 5.43 tonnes/ha/6months, respectively. There was a significantly higher DM yield at 60-day cutting interval compared to 40-day cutting interval (P<0.01). However, DM yield at 70-day cutting interval was not significant different with 40 and 50-day cutting intervals. The statistical result was found similar in the OM an ADF yield of Kudzu foliage, which had only significantly difference between the treatment 40-day cutting interval and 60-day cutting interval (P<0.01). Difference of CP yield was not significant between the cutting intervals, and CP yield of Kudzu foliage varied from 1.08 – 1.14 tonnes/ha/6months.

Effect of cutting interval on soil characteristic

Effect of cutting frequency on soil characteristic is shown in Table 1. There was no difference in pH_H2O value of the soil among cutting interval, without cutting and without Kudzu cover-crop. The OM, N_total, P₂O₅ and K₂O contents of soil with Kudzu cover-crop were higher than without Kudzu cover-crop. However, The OM, N_total, P₂O₅ and K₂O contents of soil was found similar among cutting frequencies.
 

Discussion

In the present study, the leaf dry weight proportions of foliage fell linearly from 59 to 49% by increased cutting interval (Figure 2). The leaf proportion was lower than the result presented by Manh et al (2003) where leaf dry weight proportion was 61.5%. Leaf dry weight proportion decreases as plants mature, as reported by Mbwile and Uden (1997), and D’Mello and Devendra (1995).  

Decreasing of the CP, OM contents and increasing of the DM, ADF contents by cutting interval are consistent with the many conclusions of tropical forage observations. The DM, OM and CP contents of Kudzu foliage in the present study are of the same range as reported by Gohl (1998) and Skerman et al (1988).  

The DM content in the present study is higher than the values obtained by Manh et al (2003) and Rueda et al (2003) with 20.3 and 20.5%, respectively. The report of Dongnai Rubber Company (DARUCO 2005) reported DM contents of Kudzu foliage of around 22%. In this study, total ash content was similar to the result reported by Mghen et al (1996) and Skerman et al (1988) with 5.7 and 6.5 % in DM, respectively. The CP percentage of Kudzu foliage ranged from 19.65 to 22.11% in DM basis (Table 2). The equivalent CP content results,  reported by Bermudez et al (1968, cited by Gohl 1998) and Manh et al (2003), were 19.9 and 20.3%, respectively, while the lower CP content results were reported by Rueda et al (2003), Kavana et al (2005) and Mghen et al (1996), as 17.6, 15.45 and 15.06%, respectively. The differences were probably due to difference of soil, climate and mature stage.  

Fiber percentage of Kudzu foliage varied from 38.01 to 39.94% of ADF and from 9.02 to 8.93% of lignin on DM basis. Longer cutting intervals increased ADF content, but lignin content was similar among treatments. 

Manh et al (2003) reported that the fresh yield was 15.8 tonnes/ha with four cutting times in a year. The result of this study is higher (Table 3). The DM yield in the present study was higher than the reported results by Manh et al (2003), Payne et al (1955, cited by Gohl 1998), and Crowder (1960, cited by Gohl 1998) with 3.8, 4.2 and 4 tonnes/ha. However, according to Kolawole et al (2003) and the report of Dongnai Rubber Company (DARUCO 2005) the DM yield reaches above 7 and 8 tonnes/ha after 8 months of fallow. The differences were due to difference in their harvesting and study condition. In this study, DM yield of Kudzu foliage was lowest at 40-day cutting interval (4.84 tonnes/ha/6months). The DM, OM and ADF yield of Kudzu foliage were related to change in cutting interval with R² of 0.9, 0.88 and 0.79, respectively (Figure 3). The results were also found lowest at 40-day cutting interval in term OM and ADF yield. The CP yield of all treatments of the present study was higher than s reported by Manh et al (2003), for which the CP yield was 0.78 tonnes/ha for four cutting times in a year, but less than the result of of Dongnai Rubber Company (DARUCO 2005) at the first year harvesting (1.3 tonnes/ha). 

According to FAO (2000) the soil cover is an important factor in control of erosion by water through interception and absorbing the kinetic energy in the rain. The soil cover prevents the direct impact of the raindrops and hinders the surface from becoming sealed and preservers the soil structure, as well as reducing the run off velocity and transport capacity of surface flow. In the present study, the soil characteristics were not changed with increased cutting frequency, and the foliage harvesting did not made any difference on soil characteristics compared to no cutting of foliage. But differences of soil characteristic were found between Kudzu cover-crop and without Kudzu cover-crop (Table 1).
 

Conclusions

• The present study indicates that cutting interval affects quality and yield of Tropical Kudzu foliage.

• Leaf proportions were gradually reduced to less than 50% at 70-day cutting interval.

• The quality of Kudzu foliage decreased in terms of CP and ADF by increased cutting interval.

• The yield of DM and OM reach peak at 60-day cutting interval and slightly decreased at 70-day cutting interval. The Kudzu foliage had high CP content (more than 19%) in all treatments.

• To provide a balance between quality and yield of Kudzu foliage, the optimum cutting interval was 60 days.
   

Acknowledgements

Financial support from Mekarn Project is gratefully acknowledged. The authors also thank Ms Tran Thi Phuong Dung of Nong Lam University for help with the analysis, and Mr. Dinh Cong Tien, Mr. Nguyen Ngoc Tuan, Mr. Ho Van Thinh for help with the field work.
 

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