Ammonium Fixation and Microbial Immobilisation- Mineralisation Processes can Quench N Losses in a Mollisols Located in a Sugarcane Plantation in Central Venezuela

Special Article - Sugarcane Sustainable Production

Ann Agric Crop Sci. 2020; 5(1): 1055.

Ammonium Fixation and Microbial Immobilisation- Mineralisation Processes can Quench N Losses in a Mollisols Located in a Sugarcane Plantation in Central Venezuela

López-Hernández D1* and Infante C2

¹Institute of Zoology and Tropical Ecology, Central University of Venezuela, Venezuela

²Institute of Earth Sciences, Central University of Venezuela, Venezuela

*Corresponding author: Danilo López-Hernández, Institute of Zoology and Tropical Ecology, Central University of Venezuela, Faculty of Science, Center for Applied Ecology, Apdo 47058, Caracas 1041-A, Venezuela

Received: December 30, 2019; Accepted: January 23 2020; Published: January 30, 2020

Abstract

In a Mollisols cultivated with sugarcane (Saccharum officinarum) located between Farriar and Palmarejo, Edo. Yaracuy, Venezuela, with abundance of 2:1 clay it was analyzed the ammonium fixation (NH4f) in the different horizon of the soil profile (0-200 cm), and the changes in NH4f during two crop seasons (ratoons) of the cane plantation. The soil of the experimental plot presented a high proportion of N as fixed ammonium associated to 2:1 clay, representing 18-57 % NH4f/total-N within the profile. Ammonium was mainly fixed in the silt fraction. There was a high positive correlation between NH4f and silt content, correlations however decreased in the case of the association between organic matter and cation exchange capacity with ammonium fixation, on the contrary non-association was found between NH4f and the clay content. We have found significant changes in the NH4f contents along the growth development of the sugarcane, which are associated to the application of fertilizers and the intensity of soil microbial processes, particularly mineralisation and ammonificationnitrification. The ammonium fixed in this acts as a nitrogen-reservoir, which can be released and, in turn, be available at the stages of higher crop requirements.

Keywords: Saccharum officinarum; Montmorillonite; 2:1 clay; Ammonification

Introduction

In tropical, subtropical and temperate agroecosystems, nitrogen (N), phosphorus (P) and potassium (K) have merited the greatest attention due to their essential role in crop growth and plant production processes. After nitrogen fertilization, the pathways through the N of the agroecosystem is removed are multiple. A substantial proportion of the N in agricultural production systems is subtracted through harvesting, important losses can also occur through gaseous forms by burning crop residues, volatilization and denitrification processes, while also in drainage waters inorganic soluble forms of nitrate (NO3), ammonium (NH4) as well organic N-forms are lost [1,2]. However, the soil plays an essential regulatory role in the reactions in which the N intervenes through microbial origin processes (nitrification, ammonification, immobilization and mineralisation of N).

In many areas the mineralisation of the organic matter can supply adequate plant available N to produce maximum yields. In Florida muck soils of the Everglades Agricultural Area (EAA), the annual N mineralisation can supply well over the N requirement for sugarcane; thus, N fertilization is not recommended [3]. In muck soils of the EAA, N mineralisation rates have been reported to range between 320 to 1340 lbs N acre-1 yr-1 corresponding to 97% of the total N entering the system [4]. Another important input for N balance in sugarcane agroecosystems corresponds to the nitrogen fixation by free-living organisms associated with the rhizosphere [5]. Sugarcane has been growing in some Brazilian sites for years without fertilizer additions as one indication that N-fixing plays an important role in the nitrogen self-sufficiency of this crop [6].

However, the annual harvest of sugarcane (around 60-100 Mg ha- 1), together with the burning of the crop before harvesting, a common practice of management of sugarcane plantations in South America, leads to the loss of significant amounts of nutrients (N,P and K) in the agroecosystems [7,8]. In Venezuelan sugarcane plantations, the harvest is done manually, thus plantations; require previous burning, an operation which leads directly to atmospheric emissions (CO2, N gases and generation of ozone) and the production of huge amounts of ashes. Those prescribed burning, apart from the environmental deterioration, could progressively diminish the level of soil organic matter and increase nutrient deficiency in soils [9,10], particularly in elements with gaseous biogeochemical cycles as N and S [11] and/ or losses and redistribution of some elements with sedimentary cycles e.g. P and K, among others [10,11]. Moreover, the deposition of reactive nitrogen has increased in the last three decades in the northern hemisphere specifically in North America and Western Europe and it has been identified as an important factor related to global environmental change with impacts on biodiversity and human health [9,12].

On the other hand, if soil mineral materials are appropriated, a significant accumulation of ammonium can occur in the different horizons of the profile, a process known as ammonium fixation. Fixed ammonium (NH4f) is defined as adsorption or absorption of ammonium ions by the mineral or organic fraction of the soil in such a way that these ions are not easily interchangeable to the solution [13-15]. Ammonium fixation is a process that occurs mainly in soils where secondary phyllosilicates of type 2:1 with interlaminar expansion such as vermiculite, illite and montmorillonite are abundant. On the contrary, clays of type 1:1 without interlaminar expansion by hydration such as kaolinite and halloysite do not fix significant amounts of ammonium, while amorphous clays (e.g. allophane) have no ammonium fixation at all. In agricultural systems must be differentiated the ammonium natively fixed from that “artificially’ fixed, thereby, referring to the ammonium originally retained during soil formation processes, and an additional fixation (adsorption) product of the application of ammonium fertilizers or generated by the internal mineralisation-ammonisation processes, respectively [15-17].

For decades, the Yaracuy River valley in central Venezuela has been a sugarcane production area, yet it has experienced, like other localities in the country, a drastic reduction in the production and weight of sugarcane crop stems [18,19]. Such situation is partially attributed to the abandonment of chemical or organic fertilisation due to the elimination of subsidies by the State. The high biomass production of the cane demands huge amount of nutrients (mainly N and K), so it is customary to fertilise with significant amounts of N and K and in a lower proportion of P.

In the area is notorious the presence of expansive clays type 2:1. Clays of that nature can immobilise significant amounts of N-ammonium that can interfere with nitrogenous and potassium fertilisation of crops [20]. This contribution provides information for a sugarcane plantation about: (i) the fixation of ammonium on the different horizons of the profile (0-200 cm) of a Mollisols characterized by abundance of clays 2:1; (ii) the changes in the contents of NH4f during two vegetative cycles (ratoons). The information obtained will be related to other processes linked to the N cycle.

Material and Methods

Study Site

The study was conducted in a sugarcane plantation near San Felipe, Yaracuy State, and Central Venezuela (10o29’44’’N and 68o31’44’’W). The experimental site is in a tropical humid climate region affected by marine aerosols with mean annual precipitation and temperature of 1479 mm and 26.8oC, respectively. The soil of the zone is a Typic Haplaquoll with significant content of carbonates, the presence of 2:1 clay (rich in montmorillonite and muscovite) and a slightly alkaline pH, in general, has a natural high fertility as presented in Table 1.