Evaluation of an elephant grass pasture mixed with black oats managed under agro ecological principles in the winter period

Marinês Fátima Sobczak^#, C J Olivo, A Mossate Gabbi, P Santini Charão, A Heimerdinger, J H Souza da Silva, Lilian Elgalise Techio Pereira, M F Ziech and Grasiela Rossarolla

Department of Animal Science, Universidade Federal de Santa Maria, RS, Brazil
#Part of MD Thesis of first author and author for correspondence: Secretaria do Programa de Pós-Graduação em Zootecnia - Universidade Federal de Santa Maria. Faixa Nova de Camobi, km 09- Campus Universitário. Santa Maria, RS, Brazil. Zip Code: 97105-900.
mzootecnia@yahoo.com.br

Abstract

The research was conducted in Santa Maria, RS, Brazil, during June to October 2002, with the objective to evaluate an elephant grass pasture (Pennisetum purpureum Schum.) var. Merckeron Pinda, mixed with black oat (Avena strigosa Schreb.), managed under agro-ecological principles. The experimental design was incomplete randomized blocks with two repetitions (paddocks) and seven treatments (grazing cycles). The experimental area was fertilized during Summer 2002 with 100 kg N/ha, in form of organic manure. For evaluation of the pasture Holstein lactating cows were used. The time of occupation in each paddock was one day and the period of rest varied from 29 to 51 days, in a system of  rotational grazing. Elephant grass pasture was established in rows with 3m  distance and black oat was seeded between lines, each representing 17% and 83% of total area, respectively.

There were differences in the relative availability of elephant grass and black oat, but not in total dry matter, from the start to the finish of the 7 grazing cycles.  Crude protein level and in vitro dry matter digestibility showed a decreasing linear effect, and increasing linear effect for neutral detergent fiber. In the evaluation of botanical components of elephant grass, dead material increased during successive grazing cycles. With relation to black oat, there was a linear decrease of leaf lamina and an increase in tillers and dead material. There was no difference in stocking rate over the grazing period.

The mixture of species demonstrated that the presence of elephant grass contributed to an increase in forage biomass at the start and finish of the winter period while black oat contributed to maintain the quality of pasture during the first half of the experimental period..

Key words: agro ecology, black oat, dairy cattle, elephant grass, mixed pasture.

Introduction

A great challenge in the next years will be the development of systems of production that maintain economic productivity, without damage to the soil and environment (Kiehl 1997). The seasonality of forage production results in an acute fluctuation of the feed on offer, where the principal sources are pastures (Gomide 1997).

Among the major species studied for forage production is elephant grass (Pennisetum purpureum Schum.), a perennial grass, with high productive potential  and good adaptation to the climate in Brazil. In most tropical regions, approximately 70 to 80% of the forage production is concentrated in the rainy season (Deresz et al 2003). In the dry period, there is a decrease of production and the quality of pasture (Townsend et al 1995; Lopes et al 2003; Fonseca et al 1998). In climatic conditions of South Brazil, the seasonality in the production of elephant grass is explained by low temperatures and frosts that occur during the Winter period. According to Almeida et al (2001) and Townsend (1993), the production is high from November to March. In a study of seven varieties of elephant grass in Minas Gerais, Botrel et al (1994) observed an average production in the dry season of 4600 kg of DM/ha, corresponding to 14% of the annual production. In cool regions, where elephant grass presents high seasonality of production, the introduction of species adapted to cooler climates can contribute to more stable and higher forage yields (Pereira et al 1993). In Rio Grande do Sul, the species most utilized in the cool season is black oat (Avena strigosa) and ryegrass (Lolium multiflorum). Black oat is a preferred specie in integrated livestock-crop systems, as it has a shorter production cycle and is more precocious than ryegrass. The black oat, which is widely adapted to different conditions of soil and climate, has an advantage in supporting a greater amount of vegetative residues and, when well managed, can contribute to erosion control and, consequently, avoidance of soil degradation, thus increasing the chemical, physical and biological conditions of soils (Petrere and Matzenbacher 2001).

In conventional studies with elephant grass (under cutting or grazing), the strategy of production is, basically, the establishment of the forage in monoculture, using chemical fertilizers (Gomide 1997; Townsend 1993). The organic or agro-ecological systems of production, when compared with the conventional systems, result in less degradation of the natural resources, resulting in greater stability of the production system (Altieri 1998; Gliessman 2000).

In animal production, the agro-ecological concept implies concern for principles such as animal welfare, use of organic fertilization, use of perennial pastures, establishment of pasture with minimum mechanization, and diversified cropping systems. 

The objective of the present research was to evaluate the quality of, and production from, a mixed pasture composed of elephant grass and black oat, managed under agro-ecological principles in the region of Depressão Central do Rio Grande do Sul, Brazil.

Materials and Methods

The trial was conducted in the Department of Animal Science, Universidade Federal de Santa Maria, Brazil, during the period of April, 24^th to October, 14^th 2002. The experimental area is localized in a region denominated "Depressão Central, Rio Grande do Sul State", at 29º43´S and 53º42´W, and an altitude of 95 m. The climate of the region is classified Cfa (humid subtropical), according  to Köppen's Classification, with mean annual rainfall of 1769 mm, mean annual temperature of 19.2ºC, (being the mean of minimum temperatures of 9.3ºC in July and maximum temperatures of 24.7ºC in January), relative air humidity of 82% and sunlight of 2212 hours/year (Moreno 1961). The soil is classified as Argissolo Vermelho Distrófico Arênico (Embrapa 1999).

In September 2001, the soil was treated with dolomite limestone.  Later,  swine manure was applied at the rate of 70 kg of N/ha. Elephant grass, var. Merckeron Pinda, was planted in October 2001, along the contours at a distance of 3 m between rows. It was established from cuttings,  with four to five nodes, buried in slanting direction at 40 cm distance. In January and April , cattle manure was applied at 30 kg N/ha. During the summer period, the  elephant grass pasture (with spontaneous species between the rows), was utilized for dairy cows, in a rotational grazing system.

For the experiment, the area of 0.33 ha was divided in two paddocks. The black oat was established by broadcasting the seed between the rows  of elephant grass, in April, 24^th (paddock 1) and May, 09^th (paddock 2), using 110 kg of seeds/ha.

The period of utilization of the pasture was June, 12^th to October, 14^th 2002, according to a seven sequences of grazing of the paddocks. The system utilized was rotational grazing, with cycles varying from 29 to 51 days, and one day of occupation of the paddock. Stocking rate was adjusted according to forage availability. Holstein cows, with average weight of 530 kg and daily milk production of 14 kg, were used. Each animal received a supplement of 7.1 kg of dry matter/day (3.6 kg of maize silage and 3.5 kg of concentrate). The amount of concentrate utilized was based on amounts normally utilized in organic systems (Weller et al 2002). The stocking rate (kg of live weight/ha) was calculated from the sum of live weights of the animals, divided by number of days of each cycle of grazing. It is stressed that the animals were utilized to evaluate the pasture and not vice versa.

To estimate dry matter (DM) availability of pasture,  three representative samples (3m² each one) were cut before  grazing of the paddocks. The elephant grass was cut at 20 cm above soil level and the the black oat near at the soil. From this material, a sample was dried in the oven  at 65°C for 72 hours to determine the DM content. Another sample was used to separate the forage components and to determine botanical composition of the pasture, separating manually the fractions leaf lamina, tillers and dead material (material completely dry or with more than 75% DM). The botanical fractions were dried to estimate DM content.

Simultaneously with sample harvesting for biomass,  samples were taken to simulate grazing (Euclides et al 1992), following the observation of the feeding behavior of animals for 15 minutes, at the start of and finish of each grazing cycle. These samples were dried, ground and analyzed to determine crude protein level (CP) by micro Kjeldahl method (AOAC 1984), in vitro dry matter digestibility (IVDMD) (Tilley and Terry 1963) and neutral detergent fiber (NDF) (Robertson and Van Soest 1981).

The experimental design utilized was incomplete randomized blocks with two repetitions (paddocks) and seven treatments (grazing cycles.  Data of pasture availability, IVDMD, CP, NDF and stocking rate were submitted to analysis of regression choosing the best fit equation, according to the coefficient of determination and significance of coefficients of regression (at p<0.05). The analyses of regression and correlation were made by SAS statistical package (SAS 1990). The mathematical model adopted was: Y_IJ = m + b_i + b_1xij + e_ij ,

where:

            Y_IJ: are parameters estimated;
            i: paddocks index;
            j: grazing cycle index;
            m: general mean;
            b_i : paddocks effect;
            b_1xij: effect of regression of grazing on dependent variable adjusted to model and,
            e_ij: residual error

Results and Discussion

The availability of elephant grass (2501 kg of DM/ha) can be considered high, as the grass occupied only 17% of the area.  This result can be compared with the trial conducted by Botrel et al (1994), which during the Winter period (dry), showed a production average of seven varieties of elephant grass of 4599 kg of DM/ha, with the grass established in rows at 0.80m and submitted during the rainfall period to high levels of manure (500 kg of N, 500 kg of P₂O₅ and 100 kg of K₂O/ha). The low yield observed in August occurred due to cumulative effect of frosts during June and July, and is confirmed by the high percentage of dead material (Tables 1 and 4). There was a significant negative correlation (r= -0.86; P<0.01)  between leaf lamina percentage of elephant grass and the dead material accumulated. It was observed that the leaf lamina percentage decreased after June and was practically nil  in August. But, in September, although mean temperature continued low, there was a fast recovery, with the decrease of the dead material percentage, from 27.3 to 9.5%, from August to September (Table 2).

The black oat presented small availability in the start of grazing. The value of 777 kg of DM/ha is considered low, as the plant occupied 83% of the area. Research conducted with black oat established in monoculture, under conventional manage, presented values much higher (Frizzo et al 2003; Reis et al 1993).

The overall availability of pasture DM was practically stable with little increase during the 7 cycles of utilization. The mixture, constituted by species adapted to cool and warm climate, presented a synergistic behavior with similar offer levels of forage between June and October. In the period July and August, the black oat was most productive exactly in the period when elephant grass was affected by the lower temperatures and occurrence of frosts (Table 3). In September and October, the period of maturation of the black oat in the present research, there was an increase in the yield of the elephant grass. This stability in the production of DM during the overall period of grazing is important as it facilitates the pasture management , avoiding variations in the stocking rate necessary to maintain and adequate offer level (Roso et al 1999). This is confirmed in this research where the stocking rate did not present significant variation (P>0.05), with a mean of 457 kg of live weight/ha. In relation to pasture quality, there was a significant difference (P<0.01) in the CP level. The analysis of regression (Table 1) demonstrated a decreasing linear effect during grazing. High levels of CP were observed at the start of the experimental period, with a major participation of leaves of elephant grass and of black oat (24.7% and 69.7%, respectively) (Table 2). In this period, the participation of elephant grass was higher, demonstrating that, evenin the autumn-winter period, this specie can be a substantial source of forage both in production and quality. It is important to emphasize the choice of variety which has a higher resistance to frost (Olivo 1994).

Analysis of correlation showed that the CP level of the pasture presented an inverse relation (r=-0.76; P<0.04) with black oat availability. Thus  high production during grazing implied a reduction of protein level. Alvim et al (2003) also observed the same relation in a study of grazing pastures submitted to different levels of manure. Significant associations were found between black oat availability and IVDMD (r= 0.80; P<0.02), NDF (r= -0.88; P<0.01) and dead material (r= -0.81; P<0.02). The mean level of CP in the pasture (15.6% in DM) is superior to the value required for cows with production of 10 kg of milk/day (12.1% in DM) (Santos 2000). The value also is superior to the level (10.4%) observed in elephant grass during the dry period (Botrel et al 1994) and black oat (14.5%) manured with 30 kg of N/ha (Reis et al 1993). There is similarity with black oat submitted to continuous grazing and manure with 95 kg of N/ha (Moreira et al 2002). In this research, the organic manure (100 kg of N/ha/year) was utilized during the Summer period. Fonseca et al 1998, working with elephant grass during the dry period (April to September) in Minas Gerais,  with different occupation periods (3, 5 and 7 days), observed values of CP of 6.84 and 7.78% in years 1994-1995, respectively.

In the final periods of grazing (September to October) the NDF values were high due to accumulation of dead material (Table 4), which is explained by the maturation of the black oat and the effect of frosts on the elephant grass. There was a significant correlation (r= 0.76; P<0.05) between percentage of NDF and percentage of dead material of black oat. The values of NDF are similar to those obtained by Moreira et al (2002) for black oat (69.4%) in monoculture during the end of the grazing cycle (September).

There was significant reduction (P<0.01) in IVDMD level with increase in grazing cycle, with analysis of regression presenting a negative linear effect. The initial level of IVDMD was 70.2%, reaching 56.2% in the last grazing cycle.

With relation to botanical composition of the pasture (Table 2) it was observed that the percentage of leaf lamina of elephant grass decreased to levels near to zero in August. An inverse behavior was observed with the accumulation of dead material. The negative correlation (r= -0.82; P<0.02) between this variable and leaf lamina percentage of elephant grass confirmed this trend.

Conclusion

• The study demonstrated the viability of mixtures of  elephant grass and black oat as a means of maintaining yield and quality of a pasture for grazing dairy cows.

References

Almeida E X , Flaresso J A and Baade Esas 2001 Producción animal en pasturas com base agroecológica.; In: I Simpósio Internacional Sobre Ganaderia Agroecológica Siga 2001. La Habana, p.180-182.

Altieri M 1998 Agroecologia: A dinâmica produtiva da agricultura sustentável. UFRGS, Porto Alegre.

Alvim M J, Botrel M and Rezende H 2003 Avaliação sob pastejo do potencial forrageiro de gramíneas do gênero Cynodon, sob dois níveis de nitrogênio e potássio. Revista Brasileira de Zootecnia, 32 (1) 47-54.

AOAC (Association of Official Analytical Chemists) 1984 Official methods of analysis. 14 ed. AOAC, Washington.

Botrel M A, Alvim M J and Martins C E 1994 Avaliação e seleção de cultivares de capim-elefante (Pennisetum purpureum Schum.) para pastejo. Revista Brasileira de Zootecnia, 23 (5) 754-762.

Deresz F, Matos L L and Mozzer O L 2003 Produção de leite de vacas mestiças holandês x zebu em pastagem de capim-elefante, manejada em sistema rotativo com e sem suplementação durante a época das chuvas. Arquivo Brasileiro Medicina Veterinária e Zootecnia, 55 (3) 334-340.

Embrapa 1999 Centro Nacional de Pesquisa de Solos: sistema brasileiro de classificação de solos. EMBRAPA, Brasília.

Euclides V P B, Macedo M C M and Oliveira M P 1992 Avaliação de diferentes métodos de amostragens sob pastejo. Revista da Sociedade Brasileira de Zootecnia, 21 (4) 691-702.

Fonseca D M, Salgado L T andQueiroz D S 1998 Produção de leite em pastagem de capim-elefante sob diferentes períodos de ocupação dos piquetes. Revista Brasileira de Zootecnia 27 (5) 848-856.

Frizzo A, Rocha M G and Restle J 2003 Produção de forragem e retorno econômico da pastagem de aveia e azevém sob pastejo com bezerras de corte submetidas a níveis de suplementação energética. Revista Brasileira de Zootecnia,32 (3) 632-642.

Gliessman S R 2000 Agroecologia: processos ecológicos em agricultura sustentável. UFRGS, Porto Alegre.

Gomide J A 1997 Formação e utilização de capineira de capim-elefante. In: Carvalho M M, Capim-elefante produção e utilização. Embrapa-SPI,Brasília.

Kiehl J C 1997 Adubação orgânica de culturas forrageiras. In: Favoretto V Anais do Terceiro Simpósio sobre Ecossistemas de Pastagens. FCA/UNESP, Jaboticabal.

Lopes F C F, Deresz F andRodriguez N M 2003 Disponibilidade e perdas de matéria seca em pastagem de capim-elefante (Pennisetum purpureum, Schum.) submetida a diferentes períodos de descanso. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 55 (4) 454-460

Moreira F B, Cecato U and Prado IN 2002 Composição química e digestibilidade in vitro da aveia preta, sob pastejo contínuo, no inverno. In: Reunião Anual da Sociedade Brasileira de Zootecnia, Recife, 39.

Olivo C J 1982 Efeito de forrageiras anuais de estação quente e estação fria sobre a produção de leite. M.Sc. Thesis. UFSM, Santa Maria.

Olivo C J 1994 Avaliação da preferência de cultivares de capim-elefante pastejados por vacas em lactação. Lavoura Arrozeira 47 (415) 26-30.

Pereira O G, Obeid J A andGomide J A 1993 Produtividade e valor nutritivo de aveia (Avena sativa), milheto (Pennisetum americanum L.), e de um híbrido de Sorghum bicolor x S. sudanense. Revista Brasileira de Zootecnia, 22 (1) 22-30.

Petrere C and Matzenbacher R G 2001 O papel da aveia como componente de uma agricultura sustentável. In: XXI Reunião da Comissão Brasileira de Pesquisa de Aveia - Resultados Experimentais, 21. UDESC, Lages, p.365.

Reis R A, Rodrigues L R A andCoan O 1993 Produção e qualidade da forragem de aveia (Avena strigosa). Revista Brasileira de Zootecnia. 22 (1) 99-109.

Robertson J B andVan Soest P J 1981 The detergent system of analysis and its application to human foods. In: James W P T andTheander O (editors), The Analysis of Dietary Fiber in Food.. Marcel Dekker, New York., p. 123-158.

Roso C, Restle J and Soares A B 1999 Produção e qualidade de forragem da mistura de gramíneas anuais de estação fria sob pastejo contínuo. Revista Brasileira de Zootecnia. 28 (3) 459-467.

Santos F A P 2000 Intensificação de sistemas de produção de leite. Revista Balde Branco, 426 April.

Sas. Institute Inc. 1990 SAS/STAT User's guide. Version 6,4 v.1. SAS Institute Inc., Cary, NC.

Tilley J M A and Terry R A 1963 A two-stage technique of the "in vitro" digestion of forage crop. Journal of British Grassland Society 18 (2) 104-111.

Townsend C R 1993 Avaliação de cultivares de capim-elefante submetidas ao pastejo por bovinos da raça Holandesa. M.Sc. Thesis. UFSM, Santa Maria.

Townsend C R, Olivo C J andRuviaro C F 1995 Valor nutritivo de cultivares de capim-elefante (Pennisetum purpureum Schum.) sob condições de pastejo. Ciência Rural, 25 (1) 121-126.

Weller R F, Kyriazakis I and Zervas G 2002 A comparison of two systems of organic milk production. In: Joint International Conference Organised By The Hellenic Society of Animal Production and The British Society of Animal Science, Proceedings... Athens 2002, 111-116.