A study to improve forage production of Stylosanthes guyanensis by using different inoculum and defoliation interval. Results showed that inoculum influenced the nitrogen content of the soil and defoliation interval influenced the herbage yield and the crude protein and crude fiber contents of Stylosanthes. Inoculum of Stylosanthes planted soil and 60-day cutting interval improved forage production of Stylosanthes guyanensis. It was observed that plants became more productive with an increase in crude protein content even if there is  a  decrease in crude fiber content.

INTRODUCTION

The land devoted to ruminant production in Indonesia is very large reaching almost 85% of its total agricultural land but remains to be in dry and poor condition. It has a great potential   for cattle production especially when planted with improved forage species such as legumes.

One of these species is Stylosanthes guyanensis, a perennial legume which can grow in less fertile soil, adapted to dry conditions and could fix atmospheric nitrogen. It is palatable and well liked by ruminants.

As a legume the growth of Stylosanthes guyanensis  is  influenced   by   its   nodule growth. The formation of root nodules can be stimulated by Rhizobium inoculum, the strains of which must be suited to the plant. The suitable inoculum for Stylosanthes has not yet been available in the market, so it is necessary to look for strains to be able to form more effective nodules.

Sources of inoculum for Stylosanthes can be the soil planted to it, or other inoculants used for other legume species such as the Legin for soya or the rhizobia leguminosae cover crops (Calopogonium muconoides) which are used for Vigna and Calopogonium. Harvesting of Stylosanthes is    done   by   defoliation   or   cutting    offorage at certain intervals. Defoliation interval influences both dry matter yield and growth of plant roots. Very short interval may cause death of the plants while long intervals decrease forage quality. Generally, defoliation of forage legume is 30 to 40 days and 50 to 60 days interval during the wet and dry season, respectively.

This study would determine the effect of different inoculum and defoliation interval on the formation of effective root nodules and subsequent effect on dry matter yield and forage quality of Stylosanthes.  

METHODOLOGY

The study was conducted in Rauklindungan village, Grati district, Pasuruan, East Java with an elevation of about 8 m above sea level. The soil is grumusol (vertisol), average temperature ranges from 27 to 31°C, relative humidity is 65.57%, and the yearly rainfall is 1,244 mm in the area.

Stylosanthes guyanensis variety Schofield was used in the study. Basal fertilizer consisted of 33 mg of urea; 210 mg of TSP and 140 mg KCl per kilogram soil was applied. The same amount of TSP and KCl were again applied six months after. Urea at 396 mg was added into the polybag containing 12 kg of soil after defoliation.

Analysis of nitrogen content in soil was done four times. The first was done before planting and after incubation of fertilizer (before being treated), the second when Stylosanthes were 4 months old (after receiving inoculum treatments), the third when the plants were 8 months old, and the fourth when they were 12 months old (after receiving inoculums treatments and defoliation interval).

Experimental design used was 4x3 factorial in   Randomized   Complete Block   Design   replicated three times.

The main factor was inoculum (I):

Io: without inoculum

Ii: with inoculum of Stylosanthes planted soil.

I₂: with inoculum fromCalopogonium mucunoides

I₃: Inoculum of Legin for Soya

The second factor was defoliation interval of the plant (P):  

P₀:Without defoliation (cut at

P₁:40-day interval

P₂2:60-day interval

Data collected were number of nodules, number of effective nodules,   forage production, crude protein and crude fibre contents of S. guyanensis, and the nitrogen content of soil media. The research consisted of three stages. The first stage starts from land preparation up to the time when the plant is 4 months old. This includes planting of seeds and application of Rhizobium bacteria, and early defoliation of Stylosanthes. At 4 months old, defoliation for P1 and P2 plants and analysis of nitrogen content in soil media were done. Subsequent cutting were done for the treatments. Defoliation for Po was done at 12 months old.

RESULTS

Analysis of the soil in the area showed 9.2 x 104 up to 1.8 x 105 C.F.U. (Colony Form Unit) per gram Rhizobium sp. while Stylosanthes planted soil contained 1.09 x 107 cfu per gram.

1. Incidence of root nodules
The defoliation interval did not give significant difference (P > 0.05) on the number of root nodules of 8 month-old plants, but gave significant difference (P< 0.05) on the 12-month old plants, with the highest average result of 7181.67 grains per plant obtained from P0 treatment (defoliation at 12 months old) which was not significantly different with P2 (60 day defoliation interval). This shows that nodule formation is affected by defoliation. The number of affected root nodules was not significantly influenced (P > 0.05) by inoculum, defoliation interval and their interaction.

The effect of defoliation interval on the weight of fresh root nodules was highly significant (P < 0.01) with the highest result at P0 with an average of 4.43 grams per plant on 8 month old plants and 3.78 grams per plant on the 12 month-old ones. Inoculum treatment and interaction between inoculum and defoliation interval did not give significantly influence (P> 0.05) on the weight of fresh root nodules. There was a decrease of weight and number of the root nodules on 12 month-old plants.

2. Nitrogen content in soil
In the 4 month-old plants there was an increase of nitrogen content in soil although it was not high. In the 8 month-old there was a decrease even lower than before planting, and in the 12 month-old there was a very high increase of nitrogen content (Fig. 1 and 2).  The percentage increase of nitrogen (12.50%) before planting up to 12 months old was obtained from P2 (60-day defoliation interval), and obtained from I1 (Stylosanthes planted soil) was 17.39%.

The analysis of variance showed that defoliation interval and interaction between inoculum treatments and defoliation interval did not give significant influence (P > 0.05) on the nitrogen content in soil of 8 and 12 month-old plants. The treatments of inoculum did not give significant influence (P > 0.05) on the nitrogen content in soil in 8 month-old plants, but gave significant influence (P< 0.05) on the 12 month-old ones, with the highest average resulted of 0,189% obtained from I1 (Stylosanthes planted soil), which was not significantly different from I0 (without inoculum).

Figure 1. Nitrogen content in soil for 0, 4, 8, 12 month- old  Stylosanthes, on treatments of defoliation interval.

Figure 2. Nitrogen Content in Soil for 0, 4, 8, 12 months- old Stylosanthes, on treatments of inoculum.

3. Forage production of Stylosanthes
The forage production of Stylosanthes was cumulative production during the 4 month defoliation period. During that time defoliation treatments of P0, P1 and P2 started and ended at the same time. There were two defoliation periods: when the plants were 4 up to 8 months old and 8 up to 12 months old.

The analysis of variance showed that the defoliation interval had a highly significant influence (P<0.01) on fresh and dry forage cumulative production on 8 and 12 month-old plants. The highest result obtained was P0 (1902.75 grams of fresh forage cumulative production per plant for defoliation of 8 month-old plant, and 1338.25 grams per plant for defoliation of 12 month-old plant). Followed by P2 (60-day defoliation interval). While dry forage cumulative production was 771.75 grams per plant for defoliation of 8 months-old, and 564.00 grams per plant for defoliation of 12 months old. Both of them were followed by P2 treatment.The treatment of inoculum gave highly significant influence (P<0.01) on fresh forage cumulative production of 8 month-old plants. The highest result 169.33 grams per plant was obtained on I1 treatment (inoculum of Stylosanthes planted soil) which did not significantly differ from I0 (without inoculum treatment). The inoculum  treatment was not significantly different (P>0.05) on fresh forage cumulative production for 12 month-old plants, and also on dry forage cumulative production of 8 and 12 month-old.

The interaction between inoculum and defoliation interval was not significantly different (P>0.05) to fresh and dry forage cumulative production of 8 and 12 month-old plants.

4.    Quality of forage
The defoliation interval treatment gave highly significant difference (P<0.01) on crude protein and crude fibre contents of Stylosanthes of 8 and 12 month-old plant. The high crude protein content was obtained during the 40-day defoliation interval (P1) 11.97% for 8 month-old plants and 15.24% for 12 month-old plants). Both were followed by crude protein content of 60-day defoliation interval (P2). The high crude fibre content was obtained from P0 (without defoliation interval). There were 43.99% for defoliation of 8 month-old plants and 46.75% for defoliation of 12 month-old. The lowest crude fibre content of forage was obtained on 40-day defoliation interval (P1).

The crude protein and crude fibre content of forage Stylosanthes of 8 month-old plants was highly significantly influenced (P<0.01) by inoculum treatment. The highest result of crude protein was obtained from I1 (inoculum of Stylosanthes planted soil) 11.02%, but is not statistically different from I0 (without inoculum).

The highest crude fibre of forage was 38.00% obtained from I2 (Inoculum from Legin for L.C.C. (CM), and from I3 (inoculum of Legin for Soya) 37.94%. The low crude fibre was 34. 55% obtained from I1 (inoculum of Stylosanthes planted soil), and also from I0 (without inoculum) 36.07%. The crude protein and crude fibre forage content of 12 month-old plant were not significantly different (P > 0.05) by inoculum treatment.

The interaction between inoculum and defoliation interval did not significantly differ (P > 0.05) in terms of crude protein and crude fibre contents of 8 and 12 month-old plants.

CONCLUSION

The inoculum manifested nodule formation and subsequently influenced the nitrogen content in soil, fresh cumulative forage production and forage quality crude protein and crude fiber content) of Stylosanthes guyanensis.

On the other hand, defoliation interval influenced the number of nodules, weight of nodules, fresh and dry forage cumulative production, and the crude protein and crude fibre contents of Stylosanthes guyanensis.

There are no interaction effects between inoculum and defoliation interval on all observations. The compatible inoculum for Stylosanthes is the inoculum of Stylosanthes planted soil, and the 60-day defoliation interval is the most profitable on Stylosanthes in dry land in long dry season.

Under this condition, the 4-8 month-old Stylosanthes need supplementary nitrogen in the soil media, the 8-12 month-old plants can increase nitrogen content of soil media up to 17-39% by inoculation of Stylosanthes planted soil up to 12.58 % by 60 day defoliation interval. The best quality  Stylosanthes forage is produced by using Stylosanthes planted soil and 60 day defoliation interval.

Crude protein content of Stylosanthes forage increases in proportion with the period of defoliation increase accompanied by the decrease of crude fibre content and fresh or dry forage production. The plants must be initially cut at 4 months old and subsequent cutting must be at 60 day interval.

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