Advances in the Knowledge on the Impacts of Waste Management Forest Harvesting on Soil Quality of the NE in Argentina

Advances in the knowledge on the impacts of waste management forest harvesting on soil quality of the NE in Argentina

Lupi, Ana Maria1; Fernández, Roberto2*; Martiarena, Rodolfo2; Pahr, Norberto2; Von Wallis, Alejandra2; Garcia Maria de Los Angeles3&; Aparicio, Jorge4#

1INTA-CIRN. Instituto de Suelos. N. Repetto y de los Reseros s/n (1686), Hurlingham, Buenos Aires, Argentina. E-Mail:
lupi.ana@inta.gob.ar.
Phone: 54 11 4621 2096/1448 int 124.

2INTA EEA Montecarlo. Misiones. Argentina* E-mail:
fernandez.roberto@inta.gob.ar
.

3INTA EEA Concordia, Entre Ríos, Argentina. &E-mail: garcia.mariaa@inta.gob.ar. 4INTA EEA Bella Vista, Corrientes, Argentina. #E-mail: aparicio.jorge@inta.gob.ar

ABSTRACT

There is a global debate regarding the effects of the crop residues management on the soil quality in the short and long term. In Argentina this concern has focused on the Mesopotamian region (25 ° 36’ 18" and 33 º 54’ 51" southern latitude), where is the 75% of the country's forest production. In the last 18 years, the National Institute of Agricultural Technology (Instituto Nacional deTecnología Agropecuaria, INTA) has addressed to evaluate the impacts of forest harvesting and establishment on soil fertility parameters. Until the late 90s, the type of harvesting and traditional land preparation in Mesopotamia was stem extraction and waste burning. During the 2000s, burning and remains conservation were common practices while in the last five years some companies have been incorporated the harvesting of the entire tree. This practice aims to remove some of the residual biomass of the cup for dendro-energetic purposes, which considerably avoids the organic inputs to the soil.

The main issues analyzed include the impact of nutrients, the organic matter (OM), and the physical condition of the soil in a lesser extent. Some of the studies are developed on subtropical red clay soils (Ultisols and Alfisols) in the Misiones region, using Pinus taeda and Araucaria angustifolia plantations. Quantifications performed by Fernández et al, (2000) and Martiarena et al, (2004) indicate that the amount of the remaining forest residues ranges between 29.1 to 41.1 Mg ha-1 (mulch, leaves, and up to 15 cm length branches). This amount rises to 58-66 Mg ha-1 in Eucalyptus grandis in the Entre Rios region (Lupi et al., under evaluation). From the harvesting of the whole tree in this region, Frangi et al, (1999) estimated that 234, 38 and 119 Kg.ha-1 of N, P and K respectively are obtained. Recently, Fernandez et al. (2014) estimated that a stand of P. taeda generated 25 Mg.ha-1 more residues when the whole tree is harvested than when only the stem is extracted. Under the first system, an additional loss of N, P, and K of 129.5, 7.6, and 33.3 Kg.ha-1 is expected, respectively. Other studies that simulated different harvesting scenarios conclude that the whole tree harvesting contributes the most to the major negative effects. Also, phosphorous (P) and potassium (K) are the are the nutrients that could be critical in future rotations (Goya et al, 2003;. Martiarena et al, 2010;. Martiarena et al, 2011ab; Fernandez et al, 2012ab). Other experiments at regional level analyzed the effect of different alternatives for crop residues management on the levels of total organic carbon (TOC), quality, total nitrogen (TN), and forms of P in soil. Studies under temperate conditions in the Entre Rios region compared the residues and litter removal (ER), residues conservation (CR), and residues burning (QR) considering Vertisols and Molisols. In the short term (<2 years) the CR did not increase the TOC, the Nt, or the TOC fraction associated with the supply of nutrients (particulate OM). Other treatments under the subtropical clay soils of the Misiones region showed similar trends. However, there will be short-term differential effects that are lost with time. Some analyses concluded that after the treatments were applied by 4 years, the ER and QR showed the lowest values of TOC and light carbon (Cl) (Giufre et al.2002; Lupi et al., 2007).

Another study did not detect changes in the TOC when comparing the QR vs. the CR in a similar period (Von Wallis, 2013). However, the chemical fractionation of humus evidenced the existence of changes in the TOC quality, which expose the potential consequences on the nutrient cycle linked to the organic matter. Both the QR and the ER showed an increase in the degree of MO stabilization due to the increase of the humic C-acids to fulvic C-acids ratio and the rise of CO in the most resistant fraction (humins) (Lupi et al., 2012). Recently, a short-term study on a sandy soil in the Corrientes region reported also changes in the MO quality due to the removal of crop residues (Lupi et al., 2013). The analysis of the molecular structure of the MO through the 13C NMR technique showed higher aromaticity and stability of humic acids in treatments without residues (QR or CAC), being the most marked effect on QR. The temporal evolution of chemical fertility parameters in Ultisols after 12 years of applying treatments, did not present enough evidence to conclude that the disposal of waste leads to a decrease in the levels of TOC, N, pH, and available P (Fernández et al., 2010 and Lupi et al., 2014). The input of fresh organic matter that was generated after the close of the cups and corresponding to atmospheric deposition might have offset the observed differences among treatments in the short-term assessments.

P-dynamics on the soils were also analyzed by its separation into fractions of different lability (Lupi et al. Mórtola 2012b and 2013). It was observed that the ER, QR or CR did not produce changes in the total P contained in the studied soils (Ultisol> Mollisol> Vertisol>Entisol). The organic fractions of P in Molisols, Vertisols and Entisols were not affected. The most prominent change in the Vertisols and Entisols was the increase of the available P generated by the burning without modifying the organic fractions. Controlled burning resulted to be tool for rapid nutrients transfer from the biomass residues to the first 5-10 cm of soil. On the other hand, Mortola (2013) concluded that after 9 years, the ER negatively affected the organic P fractions in Ultisols, which affects one of the sources of available P. Author did not consider the adverse effects of QR.

Regarding the physical variables, some studies (Lupi et al., 2012; Von Wallis 2013) examined the effect of different waste managements on the aggregate size in wet, the saturated hydraulic conductivity (Ksat), and the size distribution of the aggregates. It was observed that the distribution pattern of aggregate size depended upon the type of soil (Vertisol, Mollisol or Ultisol). In general, it was observed that regardless of the treatment, during the period prior to crown closure the waste conservation plays a key role on the soil protection against erosion, and on the profile of the soil-water-recharge process. In high-natural stability Ultisols, the QR, and ER in a lesser extent, affected the stability of the largest macro-aggregates, which was negatively correlated with the light fraction of the OM. In soils of the temperate region, the size distribution of aggregates did not change in the Vertisols in less than 2 years of applying the treatments. The opposite situation occurred in Molisols, where the largest macroaggregates were less stable in the ER treatments. In Vertisols the Ksat was higher than in Molisols. Additionally, the Ksat was higher in CR than in ER and QR. This was associated with a higher proportion of continuous and stable macropores, which protects the soil-atmosphere interface. On the other hand, the Molisol was naturally less stable and presented a lower Ksat regardless the presence or absence of soil cover.

Beyond the results presented here, and based on a small number of experiments, our knowledge about the effects of crop residues management on the soil productivity remains limited. However, our results provide trends of the short-term effects. Determination of the degree and extent of the impact of waste management on soil quality requires establishing long-term studies that consider different environments and species of greatest relevance. Such studies must focus on the organic carbon and nutrients dynamics and balances, soil microbiology, soil compaction.

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