Soil Quality in Relation to Forest Conversion to Perennial or Annual Cropping in Southern Brazil Elcio Liborio Balota(1)*, Ines Fumiko Ubukata Yada(1), Higo Furlan Amaral(1), Andre Shigueyoshi Nakatani(2), Mariangela Hungria(2), Richard Peter Dick(3) and Mark Steven Coyne(4)

Instituto Agronômico do Paraná, Londrina, Paraná, Brasil. Empresa Brasileira de Pesquisa Agropecuária, Centro Nacional de Pesquisa em Soja, Londrina, Paraná, Brasil. (3) Ohio State University, School of Environment and Natural Resources, Columbus, Ohio, USA. (4) University of Kentucky, Department of Plant and Soil Sciences, Lexington, Kentucky, USA. *Corresponding author. E-mail: [email protected] (1) (2)

ABSTRACT Many forested areas have been converted to intensive agricultural use to satisfy food, fiber, and forage production for a growing world population. There is great interest in evaluating forest conversion to cultivated land because this conversion adversely affects several soil properties. We examined soil microbial, physical, and chemical properties in an Oxisol (Latossolo Vermelho distrófico) of southern Brazil 24 years after forest conversion to a perennial crop with coffee or annual grain crops (maize and soybeans) in conventional tillage or no-tillage. One goal was to determine which soil quality parameters seemed most sensitive to change. A second goal was to test the hypothesis that no-tillage optimized preservation of soil quality indicators in annual cropping systems on converted land. Land use significantly affected microbial biomass and its activity, C and N mineralization, and aggregate stability by depth. Cultivated sites had lower microbial biomass and mineralizable C and N than a forest used as control. The forest and no-tillage sites had higher microbial biomass and mineralizable C and N than the conventional tillage site, and the metabolic quotient was 65 and 43 % lower, respectively. Multivariate analysis of soil microbial properties showed a clear separation among treatments, displaying a gradient from conventional tillage to forest. Although the soil at the coffee site was less disturbed and had a high organic C content, the microbial activity was low, probably due to greater soil acidity and Al toxicity. Under annual cropping, microbial activity in no-tillage was double that of the conventional tillage management. The greater microbial activity in forest and no-tillage sites may be attributed,

Received for publication on October 17, 2014 and approved on February 19, 2015. DOI: 10.1590/01000683rbcs20140675

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at least partially, to lower soil disturbance. Reducing soil disturbance is important for soil C sequestration and microbial activity, although control of soil pH and Al toxicity are also essential to maintain the soil microbial activity high. Keywords: land use, tillage, coffee, biological activity, potential mineralization, aggregate stability.

RESUMO: Qualidade do Solo em Razão da Conversão de Mata Nativa em Culturas Anual e Perene no Sul do Brasil Muitas áreas de mata nativas têm sido convertidas para o uso agrícola intensivo para satisfazer a produção de alimentos, fibras e forragem em razão do crescimento da população mundial. Assim, existe grande interesse em avaliar o efeito da conversão de florestas em áreas de cultivo agrícola, porque essa conversão interfere em várias propriedades do solo. Foram estudados indicadores microbiológicos, químicos e físicos em um Latossolo Vermelho distrófico (LVd) no sul do Brasil 24 anos após a conversão da mata nativa em área com cultura perene (cafeeiro) ou culturas anuais de grãos (milho/soja) em preparo convencional (PC) ou plantio direto (PD). O tipo de uso do solo influenciou significativamente a biomassa microbiana e sua atividade, a mineralização do C e N e a estabilidade de agregados por causa da profundidade do solo. Áreas cultivadas apresentaram menor biomassa microbiana e mineralização do C e N do que a área de controle (Mata Nativa). Apesar de a mata nativa e de o PD terem apresentado maior biomassa microbiana e mineralização do C e N do que o PC, o quociente metabólico foi de 65 e 43 % inferiores, respectivamente. A análise multivariada das variáveis microbiológicas do solo evidenciou clara separação entre os tratamentos, apresentando um gradiente do tratamento PC para a mata nativa. Apesar de o solo no cafeeiro não ser revolvido e apresentar alto teor de C orgânico demonstrou baixa atividade microbiana, provavelmente por causa da maior acidez e toxidez de Al do solo. A atividade microbiana no PD foi o dobro da observada no PC. A maior atividade microbiana na área da mata e de PD pode ser atribuída, pelo menos parcialmente, à maior estabilidade de agregados. A redução do revolvimento do solo é importante para o incremento do sequestro de C e da atividade microbiana; entretanto, o controle do pH e o da toxidez por Al do solo também são importantes para manter a atividade microbiana do solo elevada. Palavras-chave: uso do solo, preparo do solo, cafeeiro, atividade biológica, mineralização potencial, estabilidade de agregados.

INTRODUCTION An increasing world population demands more food, fiber, and forage production. To satisfy this need, many native vegetation areas have been converted to intensive cultivation. Of the more than 350 million hectares used for agriculture in Brazil, 50 % are pastures. There are also extensive areas, used for decades for perennial crops such as coffee (Coffea arabica L.) (about 2.4 million hectares) or annual crops such as maize (Zea mays L.) (9.0 million hectares) or soybean (Glycine max L.) (22.9 million hectares) (IBGE, 2014). Forest conversion to cultivated land leads to several changes in soil properties. Intense management promotes soil erosion and depletes organic matter, which decreases soil quality. Conventional or plow tillage (CT), uses traditional practices of plowing and disking to prepare the land for sowing. Tillage alters the soil structural stability (Six  et  al., 2004; Caesar-Tonthat  et  al., 2011) resulting in losses of soil organic matter (Franzluebbers, 2009) and microbial biomass (Islam R. Bras. Ci. Solo, 39:1003-1014, 2015

and Weil, 2000; Hungria et al., 2009; Frazão et al., 2010; Balota and Auler, 2011). There is great interest in agricultural practices that reduce soil degradation and increase agricultural sustainability and soil conservation. A key point in sustainable use of agricultural soil is increasing the soil C status and the processes relating to, or at least maintaining, levels close to the original ones. One of these practices is no-tillage (NT), which corresponds to sowing directly through mulch and litter with minimal soil disturbance. The area devoted to NT systems in Brazil (31 million hectares) has increased almost 10-fold in the last 10 years, corresponding to 40 % of the annual cropland (Febrapdp, 2014). Soil and crop management directly influence physical, chemical and biological soil properties, which are used to measure soil quality, which means the capacity of soil to serve a desired function, such as sustainably provide food, fiber and forage (Doran and Parkin, 1994). Microbial parameters have been successfully used to evaluate soil quality (Frazão et al., 2010; Kaschuk et al., 2010). For example, soil microbial biomass is a source of labile nutrients and an agent for transformation

Soil Quality in Relation to Forest Conversion to Perennial or Annual Cropping... 1005

and cycling of organic matter and plant nutrients. Microbial biomass and activity can be used as sensitive indicators of agro-ecosystem stress or changes in soil quality. Microorganisms have a relatively high rate of turnover and quick response compared to physical/chemical properties (Brookes, 2001; Wonprasaid, 2003; Kaschuk et al., 2010). Aggregates function as a habitat for microorganisms (Six  et  al., 2004; Caesar-Tonthat  et  al., 2011; Guillou et al., 2012) and have a strong relationship to microbial population and activity.

Vermelho distrófico according to the Brazilian Classification System (Bhering and Santos, 2008), with 760 g kg-1 clay, 130 g kg-1 silt, 110 g kg-1 sand and slope of about 6 %. The climate is a humid subtropical, of the Cfa type according to the Köppen classification, characterized by a hot summer with rain in all seasons, but with a tendency to rain mainly in summer. Mean annual precipitation was about 1,600 mm for the period 1976-2011. The rainfall in January (219 mm) is four times greater than in July (53 mm). The relative humidity is about 62 % in the winter and 77 % in the summer. Typical evaporation is from 81 mm in June to 156 mm in October. The mean air temperature is 24 oC in January (from 11 to 36 oC) and 17 oC in July (from -1 to 31 oC). Sunshine occurs for 191 h in February to 238 h in August (Iapar, 2014).

This study evaluated the effect of land use and management on microbial (C and N microbial biomass and mineralization), physical (aggregate stability and mean weight diameter) and chemical (organic carbon content, pH and CEC) indicators of soil quality 24 years after forest conversion to intensive perennial or annual crops cultivation. Our hypothesis was that the beneficial aspects of no-tillage management would partially offset the transition from forest to cultivated soil in terms of the effect on measured soil quality properties. The organic C content, pH and CEC were measured because these parameters are affected by soil management and influence plant nutrition and microbial activity. Aggregate stability was measured because this physical parameter is affected by the degree of soil disturbance and microbial activity.

The agricultural areas adjacent to the forest were selected due to their similarity of soil physical and chemical characteristics according to soil profile description (Table 1) (Sidiras  et  al., 1983; Castro Filho, 1988). According to the records of the Experimental Station, the soil environment was homogeneous at the beginning of land use transition. So these agricultural sites are good representatives of long-term land use due to their initial homogeneity and proximity to undisturbed forest. The perennial crop, represented by coffee, is about 100 m from the forest site, while the conventional tillage and no-tillage sites with annual crops are about 400 m away.

MATERIAL AND METHODS

Conventional Tillage (CT): area used in an experiment for 24 years (since 1976) with a 2-year crop-rotation with wheat (Triticum aestivum L.) during winter and soybean rotation with maize each year as summer crop. The experiment consisted of plots (8 × 25 m), separated by 2 m rows, with three replications. Tillage consisted of one disk plowing and two diskings with a light

Sites and soil description The study was conducted at the Experimental Station of the Agronomic Institute of Paraná State (IAPAR), district of Londrina, State of Paraná, in southern Brazil (23° 22’ S, 51° 10’ W and 585 m altitude). The soil is an Oxisol, Latossolo

Table 1. Initial values of soil physical and chemical properties Horizon

Layer

Sand

cm

Silt

Clay

OC

pH(H2O)

-1

%

g kg

CEC cmolc dm

P -3

mg kg-1

CT - NT(1) Ap1

0-8

11.0

13.0

76.0

16.0

5.9

14.2

3.2

Ap2

8-20

8.0

13.0

79.0

16.0

5.1

11.7

2.4

Coffee(2) Ap1

0-14

3.2

12.0

84.8

19.4

4.4

9.70

5.9

Ap2

14-24

2.5

11.0

86.5

8.2

4.4

9.01

1.6

A1

0-16

5.2

11.0

83.8

21.3

4.2

12.82

2.3

A3

16-40

3.4

12.0

84.6

14.3

4.1

10.61

1.5

Forest

(1)

Samples were collected after preparing the area for establishment of the experiment (1976). (2) Samples were collected after 10 years of coffee production (1986). CT: conventional tillage; NT: no-tillage; OC: organic carbon; CEC: cation exchange capacity.

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harrow to level the soil and prepare the seedbed. Crop stubble is tilled conventionally (plowed to a depth of 20 cm) after harvest, in fall and spring every year. Fertilizers were regularly distributed in the tillage treatments before each crop cycle, consisting of: N 95, P 55, and K 42 kg ha-1 yr-1, for the last 24 years. Nitrogen fertilizer was never applied to soybean. No-Tillage (NT): same experimental area described for the CT site. No-tillage consisted of sowing on undisturbed soil into a narrow opened trench. Crop stubble was mostly left on the surface after harvest in fall and spring every year. Coffee (CO): coffee plantation (about 4,500 m2) of cultivar “Mundo Novo”, with 2200 trees ha-1 (spacing 4.0 × 2.0 m), since 1976. Fertilization according to soil analysis before/during the growth season (Nov-Feb), on average 150 kg ha-1 yr-1 N, 40 kg ha-1 yr-1 P2O5, and 80 kg ha-1 yr-1 K2O for the last 24 years. Before planting and every three years, dolomitic lime was applied to the whole area. Forest (FO): The forest site (4.5 ha) is a remnant of primary tropical semi-deciduous forest that used to cover the north of Parana State. Leguminosae, Myrtaceae, Euphorbiaceae and Lauraceae are the main families of flowering plants at the site and the forest canopy height can reach 15 m. Soil sampling Composite soil samples (consisting of five sub-samples each) were taken from each replicate of the NT and CT sites from three layers (0-5, 5-10 and 10-20 cm) in March 2000, at the end of the summer growing season (maize). The FO and CO sites were divided into three parts according to slope (high, medium and low). From each part, a central area (50 × 70 m for FO and 20 × 60 m for CO) was considered a sampling unit from which 10 soil sub-samples (about 150 g each) were taken in a zigzag pattern, at 10 m intervals, to compose one replicate composite for each layer (0-5, 5-10 and 10-20 cm depth). In the CO site the sub-samples were evenly divided between samples taken near the edge of the tree canopy, in the planting row, and in the inter row. The fresh soil samples were sieved (