J. Agr. Sci. Tech. (2017) Vol. 19: 245-257 Mollisol: Biological Characterization under Zero Tillage with Different Crops Sequences L. B. Silvestro1, F. Biganzoli2, H. Forjan3, A. Albanesi4, A. M. Arambarri5, L. Manso3, and M. V. Moreno1, 6* ABSTRACT Zero tillage practices have a direct effect on soil microbial communities modifying soil productivity and sustainability. The crop sequences used can change the aforementioned properties, too. In this study, we evaluated the effect of crop sequences under zero tillage management on soil biological and chemical properties including vertical distribution of soil organic carbon, soil basal respiration, and dehydrogenase, acid phosphatase, and urease activity along a seasonal year and at different soil depths. The sequences included in this study were: (I) Single crop per year (sunflower-wheat-sorghum-soybean); (II) Mixed agriculture/livestock with pastures, without using winter or summer forages (wheat sorghum/soybean-canola-pasture); (III) Winter management (wheat-canola- barley-late soybean); (IV) Mixed with annual feed crop (wheat-oat/Vicia sativa- soybean or sunflower), and (V) Intensive management (wheat-barley-canola, with alternation of soybean or late soybean). Soil organic carbon decreased with increasing depth, depending on sequences (Pseq×depth= 0.0173). Soil basal respiration was higher in the 0-5 cm layer than in the 10-20 cm layer of the topsoil irrespective of the crop sequences (Pdepth= 0.0062). Dehydrogenase, acid phosphatase and urease activity were affected by crop sequences, sampling season, and depth. Mixed sequences (sequences II and IV), including perennial pastures or annual feed crop could favor dehydrogenase and phosphatase activity. Sequences with cover crops (sequences II and IV) could favor microbial activity and, therefore, improve soil quality. Keywords: Basal respiration, Enzyme activities, Microbial activity, Soil organic carbon. INTRODUCTION intended to increase soil Organic Carbon (OC) as compared to conventional tillage Crop management practices can change (Mishra et al., 2010) and the effect on soil chemical and physical properties productivity and conservation of soil affecting the activity of microbial resources is known (Apezteguía et al., communities, the activity of soil enzymes 2009). Rotation practices under zero tillage and, as a consequence, the sustainability of systems have a beneficial effect on the soil the overall system. Zero tillage systems were and could favor conservation of soil _____________________________________________________________________________ 1 Laboratory of Functional Biology and Biotechnology (BIOLAB-INBIOTEC-CONICET-CIC), National University of the Center of the Province of Buenos Aires, Argentina. * Corresponding author; e-mail: [email protected] 2 Department of Quantitative Methods and Information Systems, Faculty of Agronomy, University of Buenos Aires, Argentina. 3 Barrow-INTA Experimental Station, Tres Arroyos, Province of Buenos Aires, Argentina. 4 Chair in Microbiology and Ecology, Agricultural Faya National University of Santiago del Estero, Argentina. 5 Spegazzini Institute, FCNyM, National University of La Plata, Argentina. 6 Agricultural Microbiology, Faculty of Agronomy, National University of the Center of the Province of Buenos Aires, Argentina. 245 ______________________________________________________________________ Silvestro et al. moisture, increase soil enzymatic and The aim of this study was to evaluate biological activities and reduce the use of short-term changes due the crop rotation fertilizer (Franzluebbers, 2007). On the other practices under zero tillage and sampling hand, application of continuous cropping procedures (season and depth) on OC, BR without use of pastures for many years and enzymatic activities. decreases both OC and the total soil N concentration (Plaza-Bonilla et al., 2016). MATERIALS AND METHODS Several works showed the relationship among enzymatic activities, soil basal respiration, and OC with different Location and Management of the management of crops and sampling depths, System all concluding that tillage systems and crops had effects on soil basal respiration and We sampled a field experiment enzyme activities in the upper portion of soil established in 1997 in the Barrow (Melero et al., 2008; 2009; Paz-Ferreiro et Experimental Station (38° 19’ 25’’ S; 60° al., 2010; Wang et al., 2008). Also, climatic 14’ 33’’ W), Tres Arroyos, Buenos Aires and seasonal conditions in cultivated areas Province, Argentina. The experimental site are a limiting factor for accumulation of OC had a slope of 2-3 %, and the top soil had in the top layer of soil and enzymatic a sandy clay loam texture (259 g kg-1 of activities (Melero et al., 2009). clay, 269 g kg-1 of silt and 472 g kg-1 of Crop management has a direct effect on sand) (USDA, 2006). The soil was the microbial community and could be classified as a Petrocalcic Argiudoll (depth evaluated using soil biological and/or of the petrocalcic horizon is 50 cm) (SSS, chemical properties (Melero et al., 2011). 2014). The agro-climatic conditions of the Soil basal respiration and enzymatic experimental site are shown in Table 1. activities allow the evaluation of microbial Additional detailed soil characterization at status and soil physicochemical conditions. the experimental site can be found in Soil basal respiration gives evidence of the Table 2 and Silvestro et al. (2013). The soil carbon availability to microorganisms plots were arranged in a randomized and was used as a measure of the total complete block design and the treatments microbial activity (Ananyeva et al., 2008). (crop sequences) randomized, using three Additionally, the activity of several enzymes replicates of 420 m2 plot area (14×30 m). has been related to the organic matter The crops used in the sequences were concentration and provides early indication wheat (Triticum aestivum L.), sorghum of change in soil properties associated with (Sorghum vulgare Pers.), soybean cropping practices (Qin et al., 2010). (Glycine max L.), canola (Brassica napus Enzymatic activities have also been used as L.), barley (Hordeum vulgare L.), oat soil quality indicators in agricultural soils (Avena sativa L.), sunflower (Helianthus because they show sensitive responses to annuus L.), and vicia sativa (Vicia sativa soil changes and are related to the cycle of L.). Sequences consisted of five different nutrients in soil (C, N, P, S) (Geisseler and crop rotations: (I) Single crop per year Horwath, 2009; Qin et al., 2010). (sunflower-wheat-sorghum-soybean); (II) Therefore, different crop sequences Mixed agriculture/livestock with pastures, produce different changes in soils under zero without using winter or summer forages tillage systems. Soil chemical and biological (wheat sorghum/soybean-canola-pastures); properties are commonly used as early (III) Winter management (wheat-canola- indicators of such changes. However, these barley-late soybean); (IV) Mixed with changes can be influenced by sampling annual feed crop (wheat-oat/Vicia sativa- procedures. soybean or sunflower), and (V) Intensive management (wheat-barley-canola, with 246 Mollisol and Biological Characterization ________________________________________ alternation of soybean or late soybean). The cultivars used were Quilmes Ayelen (barley); SW 2836 (canola); A 4613 RG (soybean); A 3726 RG (late soybean); Bonaerense Maja (oat); DK 61 T (sorghum); BIOINTA 2001 (wheat) and DK 3920 (sunflower). Cropping practices involved seeding crops with herbicide application (glyphosate, metsulfuron- methyl, dicamba and 2,4-D) pesticides and simultaneous application of inorganic fertilizers (PDA- diammonium phosphate and urea) (Table 3). Sequence II had a period of three years with pasture and sequence IV had a period with pasture every two years during the 13 years of experiment. The two mixed sequences, i.e. II and IV, had a grazing period while the three remaining sequences I, III, and V were exclusively agricultural. Sequence I was associated with the “traditional” farming in the region with one crop per year. Sequence V was related to management applied by big companies, with the intensification of crop rotation (double annual cropping). Sequence III started with a sequence of one crop per year during six years and then soybean was included as a double crop on the basis of winter crops. Soil Sampling Procedure The samples were taken at 3 different times: in summer (December 2009) when the wheat was harvested; during autumn (April 2010) when sequence II had pastures established, whereas sequence IV was covered with oats; at this particular sampling time, sequences I, III, and V were in fallow; and during winter (August 2010), at the fallow period for all the studied sequences. Soil samples (roughly 2 kg) were taken with a hydraulic borer and each cylinder was divided at 0-5, 5-10, and 10-20 cm depth intervals. Soil pH was determined by potentiometric method in a soil:water ratio of 1: 2.5, according to USDA-NRCS (2004). 247 ______________________________________________________________________ Silvestro et al. Table 2. Soil pH values in the 1997, 2004, and 1982). 2010 years. Dehydrogenase and acid phosphatase activities were determined according to Soil pHa Sequenceb Tabatabai (1994), while urease activity was 1997 2004 2010 determined according to Nannipieri et al. I 6.6 6.0 5.5 II 6.6 6.0 5.2 (1980). III 6.6 5.8 5.7 IV 6.6 6.1 5.9 Statistical Analysis V 6.6 5.9 6.0 a pH: Potentiometric method (1:2,5; Soil: Water) To compare