Mineral balance and absorption from soil of Pennisetum sp at different stages
Abstract
Forage availability, in quantity and quality, is essential for livestock development. In this context, the aim of thIs study was to characterize the macro and micro elements of Maralfalfa grass (Pennisetum sp) in function of different harvest frequencies under subsurface drip irrigation. The results showed that mineral concentration in plants depends on: (i) the retention in soil and/or elapsed time for nutrient to be available after a manure application. In this sense, due to the large P retention capacity of Andosols, soil P and Mg mineralization were very slow, in spite of root activity and its influence in the soil balance (ii) the age of the plant: all element concentrations decreased as the plant grew old, except Na. The concentration values between leaf and sheath showed significant differences for all elements except for P and Cu. Thus Ca, Mg, B, Fe and Mn content s were significantly higher in leaf than in sheath while K, Na and Zn were lower in leaf. B contents were also higher in leaves. The ratio K/ (Ca+Mg) for all ages of the plant was higher than 2.2, increasing the possibility of induced hypocalcaemia. Keywor ds— Maralfafa, mineral uptake, nutrient concentration, ratio K/Ca, soil depletion .
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Introduction
Forage availability is a crucial issue for livestock development. In arid and semi arid regions, marked seasonal fluctuations in nutritional quality of natural pastures compromise livestock productivity (Madzonga and Mogotsi, 2014). To avoid this problem, it is necessary to import the forage or to continuously produce it using irrigation. In the Canary Islands, a large percentage of production costs depend on imported feed, representing economical and strategically problems for the farmer (Palacios et al., 2013). Recently Maralfalfa grass has been introduced in Canary Islands for animal diet. This grass has a high yield. The nutritional value of Maralfalfa grass has been described by Clavero and Razz (2009), Macoon et al. (2001), Correa (2006), Marquez et al. (2007) and Palacios et al. (2013). All authors agree in plant-age dependence of the mineral nutritive values. Although there is not enough information about mineral composition, it has an important role into the metabolic routes in healthy and productive animals. Mineral deficiencies can have devastating consequences on animal health. An inadequate diet can be induced lower animal production. Usually if forage harvested and offered to animals has low quality, limiting animal performance, leading the producer to make use of complementary feeding of the flock, burdening production costs (Townsend et al., 1994). The availability of mineral nutrients in appropriate quantities is a major factor for livestock, but their study is often scarce, not taking into account the fertilization and the mineral availability in the soil at harvest. A correct soil nutrient balance is essential for obtaining a sustainable high productivity. The plant must obtain all nutrients from the specific soil with which has content; therefore in this sense the soil-plant relationship is direct (Reid and Horvath, 1980). There appears to be a definitive role of mineral deficient soils to cause deficient levels in ration (Mcdowell and Conrad, 1990), but the concentration of a mineral in a soil in is an uncertain guide to its concentration in the forage (Khan et al., 2004). In a sustainable point of view, the nutrient quantities absorbed by plants must be added to the cultivated soils to avoid future deficiencies.
Manure is the main source of organic fertilizer and its appropriate management is an excellent alternative to provide nutrients to plants while improving the soil physical and chemical characteristics. This work has the objective to characterize the mineral composition of Maralfalfa grass (Pennisetum sp) grown on a recent volcanic soil through different cut-off frequencies under drip irrigation in Canary Island conditions, to obtain the optimum nutritive values.
Conclusion
All the macro and micro nutrients in Maralfalfa and for all the ages of the plant presented an adequate concentration for ruminant nutrition, except when coincided low content, high retention in soil or no enough time for nutrient to be available after a manure application (Ca, Zn and P respectively in our conditions). In this sense, our results demonstrated an imbalance on K/Ca in Maralfalfa plants. Thus, in order to avoid hypoglycemia problems when using exclusively this specie in ruminant diet, Maralfalfa must be complemented with other fodders species.
Only the Na content in plant showed significant increments as the plants grew old, contrary that occurred by the rest of the elements. Although references about the depletion of K and Ca in soils cultivated with Maralfalfa as a result as plant extractions are scarce, this fact explain the lower contents in plants found in the 3th harvest. Thus, this high yielding crop needs the addition of great quantity of nutrients to avoid soil depletion.
Ca, Mg, B, Fe and Mn contents were higher in leaf than in sheath while for K, Na and Zn were lower in leaf. As the plant grows up, leaf and sheath proportion decrease and, consequently, influences the macro and micro nutrient content. Also, our data demonstrate that soil has a critical influence in plant nutritive value.