Abstract
Tillage operation and fertilizer type play important roles in soil properties as far as soil microbial condition is concerned. Information regarding the simultaneous evaluation of the effect of long-term tillage and fertilization on the soil microbial traits of soybean farms is not available. Accordingly, it was hypothesized that, the microbial biomass and enzyme activity, more often than not, respond quickly to changes in soil tillage and fertilization. Therefore, the experiments were aimed at analyzing the responses of soil microbial traits to tillage and fertilization in a soybean field in Kurdistan University, Iran. The field soil is categorized into coarse Loamy, mixed, superactive, calcareous, and mesic Typic Xerorthents. The experiments were arranged in split plot, based on randomized complete block design with three replications. Main plots consisted of long-term (since 2002) tillage systems including conventional tillage (CT), minimum tillage (MT), and no-tillage (NT). Eight fertilization methods were employed in the sub-plots, including (F1): farmyard manure (FYM); (F2): compost; (F3): chemical fertilizers; (F4): FYM + compost; (F5): FYM + chemical fertilizers; (F6): compost + chemical fertilizers; (F7): FYM + compost + chemical fertilizers and (F8): Control (without fertilizer). The highest microbial biomass carbon (385.1 μg) was observed in NT-F4 treatment. The NT treatment comparatively recorded higher values of acid phosphatase (189.1 μg PNP g−1 h−1), alkaline phosphatase (2879.6 μg PNP g−1 h−1) and dehydrogenase activity (68.1 μg PNP g−1 h−1). The soil treated with a mixture of compost and FYM inputs had the maximum urease activity of all tillage treatments. Organically manured treatment (F4) showed more activity in dehydrogenase (85.7 μg PNP g−1 h−1), acid phosphatase (199.1 μg PNP g−1 h−1), and alkaline phosphatase (3183.6 μg PNP g−1 h−1) compared to those treated with chemical fertilizers. In NT-F4 treatment, using on-farm inputs is most suitable for sustainable management and improvement in soil biological activities in soybean cultivation. We concluded that applying organic manures and employing reduced tillage systems increased soil microbial biomass and enzyme activities.
Highlights
Tillage operations, which use moldboard plowing and disking to prepare soil for sowing, can decrease soil microbial activity and organic matter (Gupta and Germida, 1988; Mohammadi et al, 2012)
The size of the main plots was 15 × 20 m while the space between them was three meters. They consisted of long-term tillage systems including moldboard plowing with an average depth of 30 cm + two shallow disks, and chisel plowing with an average depth of 15 cm + one shallow disk, and no-tillage (NT) where crop residues cut by the combine were chopped and spread evenly with a combine-attached chopper
Applying organic fertilizers in the absence of tillage system resulted in an increase in the Microbial biomass carbon (MBC), while chemical fertilizers and minimum and conventional tillage systems did not bring about any changes (Figure 1)
Summary
Tillage operations, which use moldboard plowing and disking to prepare soil for sowing, can decrease soil microbial activity and organic matter (Gupta and Germida, 1988; Mohammadi et al, 2012). Continuous use of conventional tillage (CT) system, changes the physical, chemical, and biological properties of the soil (Lupwayi et al, 2012), the need is seen for alternative systems that reduce soil degradation and improve agricultural sustainability (Balota et al, 2004). Using minimum tillage practices for instance, can improve such physical, chemical and biological properties as macro-pore structure, aggregate stability, nutrients availability, and the diversity of microbial populations while reducing soil disturbance. In addition to providing necessary nutrients for crops and improving soil physico-chemical properties, organic fertilizer is able to enhance soil microbial activity of soil, such as improving activity of soil enzymes and increasing soil microbial biomass (Sun et al, 2003; Lv et al, 2005; Mao et al, 2008). Co-application of organic manure and chemical fertilizers is a significant approach to maintain and improve soil fertility, and increase fertilizer use efficiency (Ming-gang et al, 2008)
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