Plant and Soil (2006) 279:307–325 DOI 10.1007/s11104-005-2155-1
Ó Springer 2006
Soil carbon, nitrogen and phosphorus dynamics as affected by solarization alone or combined with organic amendment Antonio Gelsomino1,4, Luigi Badalucco2, Loretta Landi3 & Giovanni Cacco1 1
Dipartimento di Biotecnologie per il Monitoraggio Agroalimentare ed Ambientale (BIOMAA), Universita` Mediterranea di Reggio Calabria, Feo di Vito, I-89060, Reggio Calabria, Italy. 2Dipartimento di Ingegneria e Tecnologie Agro-Forestali, Universita` di Palermo, Viale delle Scienze 13, I-90128, Palermo, Italy. 3Dipartimento di Scienza del Suolo e Nutrizione della Pianta, Universita` di Firenze, Piazzale delle Cascine 28, I-50144, Firenze, Italy. 4Corresponding author* Received 14 April 2005. Accepted in revised form 12 August 2005
Key words: chloroform fumigation–extraction, labile N, microbial biomass, organic amendment, soil organic matter, soil solarization, water-soluble P
Abstract Soil solarization, alone or combined with organic amendment, is an increasingly attractive approach for managing soil-borne plant pathogens in agricultural soils. Even though it consists in a relatively mild heating treatment, the increased soil temperature may strongly affect soil microbial processes and nutrients dynamics. This study aimed to investigate the impact of solarization, either with or without addition of farmyard manure, in soil dynamics of various C, N and P pools. Changes in total C, N and P contents and in some functionally-related labile pools (soil microbial biomass C and N, K2SO4-extractable C and N, basal respiration, KCl-exchangeable ammonium and nitrate, and water-soluble P) were followed across a 72-day field soil solarization experiment carried out during a summer period on a clay loam soil in Southern Italy. Soil physico-chemical properties (temperature, moisture content and pH) were also monitored. The average soil temperature at 8-cm depth in solarized soils approached 55 °C as compared to 35 °C found in nonsolarized soil. Two-way ANOVA (solarizationorganic amendment) showed that both factors significantly affected most of the above variables, being the highest influence exerted by the organic amendment. With no manure addition, solarization did not significantly affect soil total C, N and P pools. Whereas soil pH, microbial biomass and, at a greater extent, K2SO4-extractable N and KCl-exchangeable ammonium were greatly affected. An increased release of water-soluble P was also found in solarized soils. Yet, solarization altered the quality of soluble organic residues released in soil as it lowered the C-to-N ratio of both soil microbial biomass and K2SO4-extractable organic substrates. Additionally, in solarized soils the metabolic quotient (qCO2) significantly increased while the microbial biomass C-to-total organic C ratio (microbial quotient) decreased over the whole time course. We argued that soil solarization promoted the mineralization of readily decomposable pools of the native soil organic matter (e.g. the microbial biomass) thus rendering larger, at least over a short-term, the available fraction of some soil mineral nutrients, namely N and P forms. However, over a longer prospective solarization may lead to an over-exploitation of labile organic resources in agricultural soils. Manure addition greatly increased the levels of both total and labile C, N and P pools. Thus, addition of organic amendments could represent an important strategy to protect agricultural lands from excessive soil resources exploitation and to maintain soil fertility while enhancing pest control.
* FAX No: +39 0965 311092. E-mail:
[email protected]
308 Introduction Solarization is a common agricultural practice for disinfesting soil that is accomplished by passive solar heating of moist soil covered with plastic sheeting (Katan et al., 1976). The principles of soil solarization and its multiple mechanisms of action for managing plant pathogens have been well defined (DeVay and Katan, 1991). The most obvious and known action mechanism involves the reduction of soil-borne inoculum of crop pests including fungal, bacterial and nematode pathogens, as well as insects and weeds by direct thermal inactivation (Hasing et al., 2004; Lalitha et al., 2003; Stapleton, 1996; Stevens et al., 1990), which is achieved at soil temperatures ranging from 40 °C to more than 60 °C (Stapleton, 2000). In fact, even though thermal sensitivity of target pests may vary widely among species, temperatures above 50 °C for at least four weeks have been frequently reported in solarized soils (Arora, 1998; Streck et al., 1996). Additional effects induced by soil solarization regard shifts in microbial population and activity, along with changes in soil physical and chemical properties (Chen et al., 1991). All these factors may provide a potentially active form of biological control of plant pathogens through the establishment of soil suppressiveness – defined as the capacity of soils to restrict the survival and activity of plant pathogens – (Alabouvette et al., 1996). Yet, the efficiency of soil solarization can sometimes be greatly improved by combining it with the incorporation of various organic amendments such as composts, crop residues, green and animal manures (Gamliel and Stapleton, 1993a; Gamliel et al., 2000; Haidar and Sidahmed, 2000; Harender, 2004; Ozores-Hampton et al., 2005; Stevens et al., 2003). Beneficial effects of organic amendments are related to an altered composition of the soil microbiota that would favour biological control over a broad spectrum of soilborne plant pathogens (Hoitink and Boehm, 1999; Spadaro and Gullino, 2005), and to an increased release of toxic volatile compounds originating from the decomposing organic materials when heated (Gamliel and Stapleton, 1993b; Gamliel et al., 2000). At the present soil solarization is agriculturally practiced mainly in warm locations such as California and many Mediterranean countries,
which are characterized by high air temperature during summer periods. In Southern Italy, for instance, soil solarization is commonly practiced against a wide range of plant pathogens and pests (Cartia, 1998). Indeed, in the near future its use is expected to greatly increase as methyl bromide, a synthetic chemical toxicant, which is nowadays considered the best chemical soil fumigant, will be phased out due to its ozone-depleting properties (Bell et al., 1996). The increasing popularity of soil solarization as an alternative non-chemical approach for managing soil-borne pathogens has led to plenty of studies in last decades both on the efficacy and feasibility of the technique in various agricultural productive systems (Stapleton, 2000; Stevens et al., 2003), and on qualitatite and quantitative alterations induced in soil microbial ecology (Chen et al., 1991; Stapleton and DeVay, 1984). Nevertheless, an increased release of soluble nutrients (inorganic N forms, extractable P and K, available cations and dissolved organic matter) due to soil solar heating, and related improved plant growth and yield increase were shown either under field-scale (Chen et al., 2000; Ghini et al., 2003; Salerno et al., 2000; Stapleton et al., 1985; Stevens et al., 1991a) or growthchamber simulated solarization (Gru¨nzweig et al., 1999). Similarly, other field studies relating the impact of solar heating on soil microbial activity and nutrient processes showed that N transformations (ammonification, nitrification) and P mineralization were higher in solarized soils as compared to nonsolarized soils (Stevens et al., 1991b). Nevertheless, in solarized soils direct effects on biota (shifts in populations of beneficial and harmful microorganisms) and indirect effects mediated by biota (release of mineral nutrients, turnover of soil organic matter) are probably interrelated (Gamliel and Katan, 1991; Kaewruang et al., 1989). Hence, a more integrated understanding of dynamics between gross and labile pools of major soil nutrients (C, N, P) may further contribute to the knowledge of functional relationships in solarized soils, and this constituted the aim of the present work. In the present study, we investigated across the whole time course the impact of 72-day soil solarization, alone or combined with organic amendment, on the dynamics of the following
309 soil C, N and P pools: total organic C, total N, total P and total organic P, active and/or labile C, N, and P (microbial biomass C and N, K2SO4-extractable C and N, basal respired CO2C, KCl-exchangeable ammonium and nitrate, and water-soluble P). Additionally, other physico-chemical soil variables (temperature, moisture content and pH) were monitored as well.
Materials and methods Experimental design and soil sampling A field soil solarization study was conducted for 72 days using 1.51.5 m field plots located at the Agricultural Experimental Station of the Mediterranean University of Reggio Calabria (Southern Italy) on a clay loam agricultural soil (sand 34.1%, silt 32.2 %, clay 33.7%, pHH2 O 7.2±0.1, pHKCl 6.4±0.2, total organic C 14.9±1.5 g kg)1 dw soil, total N 1.72±0.1 g kg)1 dw soil, CEC 20.9±1.3 cmol(+) kg)1 dw soil, total CaCO3 10.0±0.5 g kg)1 dw soil, EC1:1 (25 °C) 271 ±18 lS cm)1, bulk density 1.23±0.04 kg dm)3). The experimental field had been cultivated (durum wheat-legumes rotation) for almost 20 years and then kept fallow for five consecutive years. The soil was ploughed few weeks before starting the experiment. The used experimental design was a randomized complete block with three replications for single treatment. Four soil treatments were set up: nonsolarized control soil (NS), solarized soil (S), manured nonsolarized soil (MNS), manure-amended and solarized soil (MS). Commercially pelleted farmyard manure (Bio-Rex, Italpollina SpA, Italy) ( pHH2 O 8.12, EC1:10 (25 °C) 7.90 dS m)1, total organic C 36%, total N 2.8%, C:N ratio of 13:1, P2O5 3%, K2O 2%, MgO 0.8%, microelements 1.5%, moisture 16%) was applied as organic amendment at 3.75 kg m)2 rate and surface (0–10 cm) incorporated into the soil before starting the trial. All plots were moistened by sprinkler irrigation to a ca 60% water-filled pore space (WFPS) the night before the experiment started. Solarization was carried out by mulching S and MS soils with transparent polyethylene (PE) sheets (70 lm thick) in June–August for 72 days. Control (NS and MNS) soils were left uncovered. Because of dry weather, plots were
irrigated, when needed, with sprinkler water in order to keep the soil moisture content around 50% WFPS. From each plot, three composite soil samples each consisting of three different soil cores pooled together (sub-replicates) were randomly collected from the upper 20-cm layer (after removing the top 2–3 cm) after 0, 1, 2, 4, 8, 16, 36 and 72 days from the beginning of the solarization experiment. Samples were taken from the middle of each plot in order to minimize the border effect of soil solarization (Grinstein et al., 1995). After short air-drying (1 day) soil samples were sieved (
