Season, fertilization, and yield of varieties of Pennisetum purpureum

Temporada, fertilización y rendimiento de variedades de Pennisetum purpureum

O. Santiago Ramos-Trejo, C. Arturo Victoria-Graniel, J. José Sandoval-Gío*

Instituto Tecnológico de Tizimín, km 3.5, final del aeropuerto Cupul s/n. 97700. Tizimín, Yucatán, México. * Author for correspondence. (jsandoval29@hotmail.com; jsandovalgio@gmail.com).

Received: November, 2014.
Approved: August, 2015.

Abstract

Pennisetum purpureum has an extended use as forage and further knowledge related to the seasonal influence and fertilization could improve its cultivation. The effects of dry and rainy season and application of fertilizers (200-60-00), on the yield of four varieties of P. purpureum (Taiwan, OM-22, Maralfalfa, CT-115), and a homogeneous mixture of them were evaluated. The study, with four replicates, was conducted at Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias, Tizimín, México, and lasted 10 months. Dry matter (DM), crude protein, leaf/stem ratio, stalks per cluster, and plant height, were assessed. Mean values of DM of all treatments in rainy season were significantly different with respect of dry season (36 and 28 t ha^-1). Dry matter in treatments with fertilizer was 35 t ha^-21 % higher than control without fertilizer (~ 29 t ha^-1). Assessment of interaction factors showed that the best mean value was for rainy season with fertilizer (~39 t DM ha^-1) and in individual evaluation, Maralfalfa and OM-22, recorded the best yield (~44 t DM ha^-1 fertilizers in rainy season). Dasometric measurements were inconstant for cultivars of the study. We suggest comparing these results with other indicators associated with rainfall and soil humidity for a better perspective of the cultivation of this species.

Keywords: Chemical composition, dry matter, tropical forages, King Napier grass, yield.

Resumen

Pennisetum purpureum tiene uso amplio como forraje y el conocimiento mayor relacionado con la influencia estacional y fertilización podría mejorar su cultivo. Los efectos de la temporada seca y lluviosa y la aplicación de fertilizantes (200-60-00) se evaluaron en el rendimiento de cuatro variedades de P. purpureum (Taiwán, OM-22, Maralfalfa, CT-115), y una mezcla homogénea de ellas. El estudio, con cuatro repeticiones, se realizó durante 10 meses en el Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Tizimín, México. La materia seca (MS), proteína cruda, relación hoja/tallo, los tallos por macollo, y la altura de la planta fueron evaluados. Los valores promedio de MS de todos los tratamientos en temporada de lluvias fueron significativamente diferentes a los de la temporada seca (36 y 28 t ha^-1). La materia seca en los tratamientos con fertilizante fue de 35 t ha^-1, 21 % mayor al testigo sin fertilizante (~ 29 t ha^-1). La evaluación de la interacción de los factores mostró que el valor promedio mejor fue el de la temporada de lluvia y fertilización (~39 t MS ha^-1) y en la evaluación individual Maralfalfa y OM-22 mostraron rendimiento mayor (~44 t MS ha^{- 1} fertilizados en temporada de lluvias). Las mediciones dasométricas no fueron constantes para los cultivares del estudio. Sugerimos comparar estos resultados con otros indicadores asociados con la lluvia y la humedad del suelo para obtener una mejor perspectiva del cultivo de esta especie.

INTRODUCTION

The increase of demand for foods from animal origin caused a tendency to intensify the use of land for livestock production (Montenegro and Abarca, 2002; Cino and Díaz, 2010). One alternative for a substantial increase of livestock productivity is the use of forage, which in tropical countries is the most economically viable source of food for ruminants. Thus, a variety of forage options utilizing optimized grass can provide large volumes of biomass of acceptable quality in tropical livestock (Argel, 2006; Sánchez et al., 2008). However, due to the fact that the forage used is generally naturalized, there are limiting factors, i.e. the marked seasonality of availability (Lamela et al., 2005) and the variation of nutritional value (dos Santos et al., 2001; Araya and Boschini, 2005).

The Pennisetum genus is used in the tropics (Aguado-Santacruz et al., 2004) and worldwide (Anderson et al., 2008) mainly due to the high forage yields of developed clones from P. purpureum (Febles et al., 2007). Araya and Boshini (2005) found high levels of dry matter (DM) from King Grass and Taiwan clones at 112 and 140 d of cutting cycles. Chacón-Hernández and Vargas-Rodríguez (2010) reported reduced protein content for this crop, with harvest cycles longer than 60 d due to the diminished leaf/stem ratio. Lounglawan et al. (2014) stated that cutting of King Napier grass in periods from 45 to 60 d produces greater DM than cutting at 30 d.

Nevertheless, with the recognized efficiency of this species, there is inconclusive evidence regarding how seasonality and use of fertilization could influence the growth of P. purpureum in the Neotropical regions. For instance, varieties of P. purpureum produce divergent results of crude protein content (Márquez et al., 2007) and production of DM when used with nitrogenized fertilizers (Cerdas and Vallejos 2010; Osorio and Rodriguez, 2010; Ramos-Trejo et al., 2013). It is possible that if seasonal effects in P. purpureum were evaluated, data regarding the yield of the crop could be defined of a better manner.

Based on the above evidence, the aim of this research was to evaluate the effect of season and fertilizer doses on the yield and quality of four varieties of P. purpureum (both individual and associated) in the Eastern region of Yucatán, Mexico.

MATERIALS AND METHODS

The study was carried out at the experimental site of the Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias (INIFAP) at Tizimín, Yucatán, México (21° 04' 27" N, 89° 31' 12" W), and lasted 10 months (February to December 2011).

The experimental design was completely randomized with a factorial arrangement of 5x2x2 (20 treatments) and four replications per treatment. Four varieties (first factor) of P. purpureum were evaluated: Taiwan, Maralfalfa, OM-22, and CT-115; the fifth option was a mixed scheme of the four grasses in alternate order and equal proportions. The second factor was the two seasons of the year (rain and dry). The third factor was fertilization with a dosage of 0 (control) and 200-60-00 (200 kg N ha^-1 and 60 kg P ha^-1), divided into applications every 90 d.

The soil is a Cambisol (FAO) or Kancab (Mayan name) with a sandy/clay-like texture, pH 6.5, and 3.5 % organic matter. The water for irrigation was salt free and as such was suitable for irrigation of grasses.

Sowing was done with vegetative material and 20 cm sticks with two knots in 10 cm deep furrows. In addition, the sowing arrangement was of 0.35 m between plants and 1 m between rows with an East-West orientation, for better sunlight exposure. Each plot consisted of six rows of 4 m length resulting in a total of 20 m², of which 12 m² were considered to be usable plots. The first fertilization was done on March (uniformity cut) and then, every 90 d using urea and 18-46-00 (18 kg N ha^-1 and 60 kg P ha^{- 1}) of diammonium phosphate. After each application of P and N, sprinkler irrigation was applied. As well as this, bimonthly weeding and extra water aspersion were carried out twice a week during the dry months. No evidences of pests or diseases were observed.

Cutting was total, removing almost all the foliar biomass (>95 % of foliage), and this labor was performed twice in the dry season and twice in the rainy season, as recommended by Solorio and Solorio (2002). In each cut, the forage yield was quantified (t DM ha^-1), taking foliage samples of approximately 300 g. Later, the stalk and leaf were separated and dried at 60 °C in a forced circulation evaporator, until a constant weight was achieved. Dry matter yield (t DM ha^-1), dry protein (DP) measured by Kjendall method, leaf/stem ratio, stalks per cluster and height of plant were the variables evaluated.

The dasometric measurements and the yield components at harvest were compared through an ANOVA for repeated measurements using the Statgraphics© for Windows 5.1. When significant differences were noted, comparison of means Tukey's test was applied (p≤0.05).

RESULTS AND DISCUSSION

A mean value of 36 t DM ha^-1 corresponded to rainy season, it contrasted with the mean value of 28 t DM ha^-1 for dry season, which was 29 % less than the first one. Also, biomass production was ~35 t DM ha^-1 with application of fertilizer (200-60-00; 200 kg N ha^-1 and 60 kg P ha^-1) (Table 1). This data represents an improvement of 21 % in production per hectare, in comparison with the control without fertilizer (29 t DM ha^-1) (p≤0.05).

Results of this research represent a complement of those obtained by Ramos-Trejo et al. (2013), they assessed the production of three varieties of P. purpureum with two different sources of N in Eastern Yucatan, Mexico, and they concluded that fertilization improved the yield of two of three varieties evaluated, but without knowing if the seasonal variation could influence the results.

Yield is important since in tropical crops, like P. purpureum, forage quality diminishes during the dry season, but it increases on the rainy season forage increases quality (Ansah et al., 2010; Osorio and Rodríguez, 2010).

Our results showed that N fertilizer increased DM of P. purpureum more than in others, studies. Thus, Cerdas and Vallejos (2010) found a lower average yield (13.5 t DM ha^-1) of P. purpureum var. Cameroon when applying between 300 kg and 450 kg of N ha^-1 year^-1 in the dry region of Costa Rica, whereas Faría et al. (1997) reportaron a mean of 18 t DM ha^-1 of P. purpureum cv. N-75 Mott, fertilized with 300 kg N ha^-1 year^-1, in a South American region. Ramos-Trejo et al. (2013) presented a mean yield of 20.94 t DM ha^-1 cut^-1 when applying 300 kg of N (urea) ha^-1 year^-1 on OM-22, CT-115 and King Grass.

An explanation of the discrepancy between these and the present research could be related to different climatic conditions during the studies. Matías and Ritt (1988) argued that environmental temperature, as result of solar irradiance, plays an important role in the interaction of climate - vegetation, as much as soil quality. Therefore, it will be necessary to evaluate the temperature and solar radiation (photosynthetic activity) effects and fertilizer amount on crops.

Espinosa et al. (2001) indicated another possible reason for the variability of results; they suggested that the differences in forage quality among varieties could be attributed to intrinsic factors. In fact, Wanjala et al. (2013) showed through genetic of population studies that cultivars of Pennisetum have a moderate genetic variability, existing information is scarce and cannot be relied upon for crop improvement. Nevertheless, under fertilization, Maralfalfa and OM-22 (200-60-00) presented high yield (39 and 38 t DM ha^-1), compared with the other crops evaluated (28 to 33 t DM ha^-1) (p≤0.05) (Table 1). Ramos-Trejo et al. (2013) indicated that OM-22 and King Grass varieties reached the highest yield of forage when were evaluated in Eastern region of Yucatán state.

For individual yield evaluation by season, Maralfalfa presented improved productive behavior (t DM ha^-1), in the dry season (31.46) and rainy (41.08), followed by OM-22 (with 29 and 39, respectively), the Mixture (with 28 and 37, respectively), CT-115 (with 27 and 35, respectively) and finally Taiwan (witj 23 and 27, respectively) (p≤0.05) (Table 1).

In the global assessment of interactions of factors, the best mean value of the forage production of all varieties corresponded to rainy season with nitrogen fertilization (39.34 t DM ha^-1 cut^-1) (p≤0.05) (Table 2). This value also represented an increase of 25 % with respect to dry season (N fertilization, 31.48, t DM ha^-1 cut^{- 1}), and it is an evident increase in forage production due to season through all varieties. Likewise, in the evaluation of crops without fertilization in the rainy season, mean of yields was significantly higher (33.13 t DM ha^-1 cut^-1), than the value of the dry season (25.12 t DM ha^-1 cut^-1) (p≤0.05) (Table 2).

These results are congruent with the explanation of Bade et al. (1985); they stated that low soil humidity affects crop yield due to its effect on biochemical aspects of the plant's photosynthetic process (Sanderson et al., 1997). Also, Deresz (2001) argued that in several regions approximately 70-80 % of production of P. purpureum is concentrated in rainy season. These effects of season are attributed to scarce precipitations and temperatures of winter.

For the evaluation of individual interaction of the A x B x C factor, the two fertilized varieties with best response in the rainy season and application of fertilizers were Maralfafa with 44.93 t DM ha^-1 cut^-1 and the OM-22 with 43.90 t DM ha^-1 cut^-1.

As it was already said, the influence ofprecipitation is considered the most important climate factor in terms of growth and quality of grass. Thus, in our study, the soil analysis showed optimal evidence of N (data no shown). However, the pluvial measurements were not contemplated within the objectives of this study and for further studies we recommend keeping a record of the precipitation and soil humidity.

In terms of dasometry, results were variable for cultivars of the study: i.e. the OM-22 variety presented a significantly higher leaf/stem ratio (p≤0.05) in comparison with the other treatments (38 % in contrast to 33 %). The clone CT-115 had an average of 37 stalks per cluster and was significantly better (p≤0.05) than the other cultivars (mean of 31 stalks per cluster). Similar data for both dasometric values were found by Ramos-Trejo et al. (2013) using OM-22 and CT-115 varieties, fertilized each one with two different N sources. The OM-22 clone and Maralfalfa presented improved plant height (p≤0.05) in comparison with the other treatments (233 or 214 cm).

CONCLUSIONS

In humid conditions of the eastern region of Yucatán State, and with soil fertilized with N and P, mean values of DM of all treatments in rainy season were better than that one's of dry season. Similarly, DM in treatments with fertilizer was higher than the control without fertilizer. In assessment of interaction factors the highest mean value corresponded to treatment during raining season and fertilization and to Maralfalfa and OM-22 for individual evaluation, among the other cultivars.

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