ORIGINAL ARTICLE

Study of the chemical soil fertility in the biomass bank technology of Pennisetum purpureum Schum cv. CUBA CT-115 with different exploitation years

Estudio de la fertilidad química del suelo en la tecnología de banco de biomasa de Pennisetum purpureum Schum vc. CUBA CT-115 con diferentes años de explotación

G. Crespo, R.O. Martínez

ABSTRACT

The change of chemical fertility of a ferrallitic red brown soil in the biomass bank technology of Pennisetum purpureum Cuba CT-115 was researched with different years of exploitation (6, 12 and 18 years, respectively). The pH indicators (in KCL), MO, N, P, K, Ca and Mg were researched. The data were subjected to variance analysis, according to simple classification model and the t-Student test was used in necessary cases. With the longer time of exploitation of 18 years, there was significant increase (P < 0.0001) of the OM (3.07 to 5.16 %), followed by the biomass bank with 12 years (3.04 to 3.71%), while the P content significantly decreased (P < 0.0056) in the biomass bank of 18 years (57.84 to 39.21 ppm),but did not varied in 12 years. The soil in the biomass bank of 6 years did not showed variation of the studied chemical indicators. The results indicated that there is an increase of the soil OM as it is higher the exploitation time of the biomass bank and P content decrease. It is recommended that, under similar soil conditions, the monitoring of the soil fertility state, mainly of the P assimilable content, from 6 years of uninterrupted exploitation with this technology.

RESUMEN

Se investigó el cambio de la fertilidad química de un suelo ferralítico pardo rojizo en la tecnología de banco de biomasa de Pennisetum purpureum Cuba CT-115 con diferentes años de explotación (6, 12 y 18 años, respectivamente). Se investigaron los indicadores pH (en KCl), MO, N, P, K, Ca y Mg. Los datos se sometieron al análisis de varianza, según modelo de clasificación simple y se utilizó la dócima de t-Student en los casos necesarios. Con el mayor tiempo de explotación de 18 años, se produjo incremento significativo (P < 0.0001) de la MO (3.07 a 5.16 %), seguido del banco de biomasa con 12 años (3.04 a 3.71%), mientras que el contenido de P disminuyó significativamente (P < 0.0056) en el banco de biomasa de 18 años (57.84 a 39.21 ppm), pero no varió en el de12 años. El suelo en el banco de biomasa de 6 años no mostró variación de los indicadores químicos estudiados. Los resultados indicaron que se produce incremento del contenido de MO del suelo a medida que es mayor el tiempo de explotación del banco de biomasa y decrece el contenido de P. Se recomienda que, en similares condiciones de suelo, el monitoreo del estado de fertilidad del suelo, principalmente del contenido de P asimilable, a partir de los 6 años de explotación ininterrumpida con esta tecnología.

INTRODUCTION

The main problem of tropical cattle is the lack of food for animals during the dry season, which could last from 6 to 7 months uninterruptedly and it is the critical period for cattle rearing.

The variety Cuba CT-115 of Pennisetum purpureum was obtained by the issue culture technique, from king grass corns at the Instituto de Ciencia Animal,  plant that proved to be able to store feed in the field for the drought period, resist grazing, has high content of sugars and produce favorable regrowth and tillering after grazing (Valenciaga et al. 2009, Fortes et al. 2012), useful characteristics to fulfill the needs of this season.

The technology for the use of Cuba CT-115 as biomass bank has had wide acceptance by the Cuban producers. The provinces Villa Clara, Cienfuegos, Pinar del Río and Granma are highlighted, whose producers considered that its productive results have been driven by sowing and the use of Cuba CT-115 in grazing. Other provinces, as Guantánamo, Las Tunas and Santiago de Cuba, consider that this technology is one of the best options for solving their current feeding problems in the dry period (Martínez 2010).

In milk production, the technology allowed increasing productivity by area, from less than 500 L ha^-1 to levels above 2000 L ha^-1 and the economic gains will exceed the 3,000 Cuban pesos (Martínez 2010). However, the effect that will have the application of this technology to long - term on the chemical characteristics of soils it is not known.

The objective of this study was to research the performance of chemical fertility of the soil, depending on the exploitation time of biomass bank technology of Cuba CT-115 in an Eutric ferrallitic red brown soil from Mayabeque province, Cuba.

MATERIALS AND METHODS

The research was conducted in an experimental dairy farm from the Instituto de Ciencia Animal, where the Biomass Bank technology of Cuba CT-115 is developed. The 100 cows from the dairy had very similar characteristics, in terms of number of lactations, milk production, age and liveweight. The grazing hours and rest in the shade buildings and the supply of mineral salts and water were similar for all animals.

The soil samplings in the biomass bank were carried out in the paddocks which have 6, 12 and 18 exploitation years, respectively. The predominant soil in this area of the dairy unit is the Eutric ferrallitic red brown, on marly limestone (Hernández et al. 2015).

Experimental procedure. First of all the representative paddocks of the biomass bank of Cuba CT-115 which fulfill with the different exploitation times indicated were selected. This was carried out from the analysis of dispersion and position statistics (X, DS and CV) for botanical composition and soil cover, so that those paddocks with the values of these statistics closer to the mean were chosen. Thus, the paddocks 6 (6years), 20 (12years) and 80 (18years) were sampled.

In each paddock of 1.5 ha each, an initial soil sampling was performed before planting Cuba CT - 115. Then, in 2014, the sampling was repeated, with the same procedure as the first time.

The soil samples were extracted with helicoidal drill, at a depth of 0 – 20 cm, in nine points distributed on the diagonals of each paddock. In each of these points, five partial samples were taken which were uniformly mixed to form 18 samples in total, formed by paddocks. These sampling were carried out at the beginning of the rainy season, that is, between 15 and 30 June.

All soil samples were air dried and then milled and passed through a sieve with holes of 1mm. 50 g of each were used for the analysis in the laboratory. To each sample was determined pH in KCl (potentiometer) and organic matter (OM) (Walkley & Black, cit. by Jackson 1970), nitrogen (N) (Latimer 2012), phosphorus (P), potassium (K) (Oniani 1964), calcium (Ca) and magnesium (Mg) (Paneque et al. 2010).

Statistical analysis of the results. A completely randomized design was applied, with two treatments and 18 repetitions. The treatments were the state of soil fertility, at the beginning and end of each exploitation time, while the repetitions were formed by the 18 sampling points in each case. An analysis of variance was performed, according to simple classification model. The t-Student test was used, in necessary cases. The statistical package proposed by Di Rienzo et al. (2012 was used.

RESULTS AND DISCUSSION

One of the most significant results in this research was the highest increase found in the OM content of the soil in the area with higher exploitation time of the biomass bank (tables 1 and 2).

In a previous research, conducted in an area near this experiment, Lok et al. (2009) found increased  of OM content and assimilable N of the soil in the  biomass bank that already had more than 10 exploitation years. In this research, the mentioned authors identified that the litter which was accumulated on the soil, and the high root development of Cuba CT-115 (up to 50 cm deep) were the main causes of that performance.

Also Crespo et al. (2004) estimated that the Cuba CT-115, which occupied 15% of the area in a diversified system, produced 2.58 t DM ha^-1 of litter in a year. Taking into account this value, it could be estimated that in 18 years (maximum time studied in this experiment) the total amount of accumulated litter may have been considerable. There is no doubt that this high amount of litter, produced by the plants of CT-115 in the biomass bank, could be the main cause of the increase of OM content in the soil.

It has been proved that detritivores soil organisms, such as millipedes (Glomeridesmida), mealybugs (Hemiptera) and snails (Pulmonata) acts above the soil surface as epigean organisms that, when feeding on litter, help to its fragmentation and begin the decomposition process, thus increasing the exhibition area for the microflora attack. The soil engineers, which are form by consumer groups of OM, such as worms (Haplotaxida), termites (Isoptera) and ants (Hymenoptera), have a specific effect within the soil, which causes changes of their physico-chemical properties with the formation of stable aggregates, which favors the movement and water retention, gas exchange and the total content of OM (Lavelle 2000).

Although with 12 exploitation years, the OM content increased with respect to the initial value (table 2) this increase was not as marked as in the bank with 18 years of continuous management , which could be due to the lower volume of litter accumulated in the first case.

The increase of Ca content in the soil in the biomass bank with higher exploitation ages (18 and 12 years) agree with that found by Crespo & Otero (2011), when researching the fertility performance of a brown soil with carbonate 1.5 years after sowing the Cuba CT-115. These authors attributed this performance to the contribution of Ca that the roots of this plant made, which in addition of having high depth and biomass than the remaining grasses that are commonly used in grasslands (Lok et al. 2009).

In the soil of the biomass bank with 6 exploitation years (table 3) there was not significant variation in the soil chemical indicators which were analyzed.

The absence of change in the values of the soil indicators in the biomass bank with 6 exploitation years indicates that, initially, the supply of nutrients in the soil was high (Oniani 1964, Paneque et al. 2010), enough to supply the Cuba CT-115 requirements with the performed management. However, the marked decrease of P content in the soil in the bank with 18 exploitation years, indicates the need to begin monitoring the state of soil fertility in these areas from 6 exploitation years.

Vanden Bygaart et al. (2010) found in 27 experiments in Canada that the re-monitoring of the soil during 30 years in the areas occupied by permanent grasslands, has shown marked OM increases in these areas, with respect to what happens in areas with annual crops.

The results of this research showed that there is increase of the organic matter content of the soil as it is higher the exploitation time of biomass bank with the Cuba CT-115 variety and, under similar conditions, will have to monitor the soil fertility state, mainly the content of assimilable P, from 6 exploitation years of this technology.

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Received: 10/06/2015
Accepted: 06/07/2016

G. Crespo, Instituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, Mayabeque, Cuba. Email: gcrespo@ica.co.cu