COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 2016, VOL. 47, NO. 21, 2396–2404 http://dx.doi.org/10.1080/00103624.2016.1243706
Soil pH and Exchangeable Cation Responses to Tillage and Fertilizer in Dryland Cropping Systems Justin L. Reeves and Mark A. Liebig USDA-ARS, Northern Great Plains Research Laboratory, Mandan, North Dakota, USA ABSTRACT
ARTICLE HISTORY
Long-term use of nitrogen (N) fertilizers can lead to fertility-lowering soil chemical changes. To examine this in geologically young soils in the northern Great Plains of North America, we present near-surface (0–7.6 cm) soil chemistry data from 16 years of two crop rotations: continuous crop (CC; spring wheat [Triticum aestivum L.]—winter wheat [T. aestivum]—sunflower [Helianthus annuus L.]) and crop-fallow (C-F; spring wheat—fallow) that underwent factorial tillage (none, minimum, conventional) and N rate (low, medium, high) treatments. For CC, the N rate (but not tillage) had a significant effect on pH, with the high N rate leading to the largest pH decline (−0.76). The nitrogen rate also had a significant effect on cation exchange capacity (CEC) for CC, whereby CEC increased with the N rate. Managers utilizing high N rates should be aware of the potential for soil acidification, even in the northern Great Plains of North America.
Received 29 January 2016 Accepted 17 May 2016 KEYWORDS
Acidification; cation exchange capacity; nitrogen (N) rate; no-tillage
Introduction Crop rotation, tillage, and fertilizer regimes are well-known to have a variety of effects on the functioning of agroecosystems. For instance, beyond productivity (e.g., Peterson and Varvel 1989; Sindelar et al. 2015; Triplett and Dick 2008), soil microbial activity and nutrient cycling can be highly influenced by management (reviewed by Alvarez 2005; Dick 1992). Important soil chemistry changes over time can also vary with management and are thus important to consider when evaluating longterm outcomes associated with cropping systems. One particularly important management-affected soil chemistry characteristic is pH. Changes in soil pH can lead to reduced plant nutrient availability and iron or aluminum toxicity, both of which can have detrimental effects on crop production (Mahler and McDole 1987; Smith and Doran 1996). Both management and environmental factors can contribute to soil acidification. In particular, nitrogen (N) fertilization can cause acidification via nitrification in near-surface soils, with increased acidification at higher levels of N application (e.g., Barak et al. 1997; Bouman et al. 1995; Darusman et al. 1991; Heenan and Taylor 1995; Schroder et al. 2011). Along with the N rate, no-tillage management has also been shown to increase soil acidification in some cases (Blevins, Thomas, and Cornelius 1977; Dick 1983; Tarkalson, Hergert, and Cassman 2006). Beyond fertilizer and tillage effects, soil water can increase or suppress near-surface acidification, with soils undergoing wet-dry cycles having suppressed acidification as compared to continuously moist soils (Paul, Black, and Conyers 1999). Crop residue removal can also facilitate acidification (Paul, Black, and Conyers 2001). Dynamics in soil pH and exchangeable base cations calcium, magnesium, potassium, and sodium (Ca+2, Mg+2, K+, and Na+) may be interrelated, as uptake or loss of such cations can lead to increased acidification rates (Bolan, Hedley, and White 1991). Previous studies have shown decreases in soil Ca+2 CONTACT Mark A. Liebig Mandan, ND 58554, USA.
[email protected]
This article not subject to US copyright law.
USDA-ARS, Northern Great Plains Research Laboratory, P.O. Box 459,
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and Mg+2 associated with increased N rates and acidification (Barak et al. 1997; Bouman et al. 1995; Darusman et al. 1991; Schroder et al. 2011). Total cation exchange capacity (CEC) can consequently be related to pH change, whereby CEC decreases with increased acidification (Barak et al. 1997). Few studies exist comparing various fertilizer and tillage treatments and how they interact to influence soil acidification (Blevins, Thomas, and Cornelius 1977; Jacobsen and Westerman 1991). Even rarer are studies that examine such interactions across multiple rotations (as did Heenan and Taylor 1995). Here, we report how near-surface (0–7.6 cm) soil pH, CEC, and exchangeable base cations (Ca+2, Mg+2, K+, and Na+) changed over 16 years in a factorial experiment consisting of three tillage and three fertilizer treatments under two different crop rotations. We focused upon nearsurface soil because multiple previous studies have shown soil chemistry changes related to management are most pronounced in the top 10 cm of the soil profile (e.g., Liebig et al. 2002a, 2002b; Liebig, Tanaka, and Weinhold 2004; Jacobsen and Westerman 1991; Rasmussen and Rohde 1989). In addition to the experimental context, this investigation offered the opportunity to explore soil responses to management in systems with geologically young, highly buffered soils typical of the northern Great Plains of North America (Soil Survey Staff 1999). As a guide to this investigation, we hypothesized soil acidification would be most pronounced in treatments with increased N fertilization, reduced soil disturbance, or continuous cropping. Additionally, we hypothesized that as soil pH decreased, so would the corresponding CEC and individual exchangeable cations.
Materials and methods The study began in 1984 (baseline data taken in 1983) near Mandan, ND, USA (46.7753, −100.9516; 592 m asl) and continued through 2001. See Halvorson, Weinhold, and Black (2002) for full site and study details. Mean annual temperature and precipitation at the study site are 4.0°C and 410 mm, respectively. The site is on gently rolling uplands (0–3% slope) with a silty loess mantle overlying Wisconsin age till, with soil pH values under native vegetation ranging from 6.4 to 6.7 in the surface 10 cm (Liebig et al. 2006). Soils at the study site were a mix of Temvik and Wilton silt loams (finesilty, mixed Typic, and Pachic Haploborolls) with inclusions of Belfield-Grail clay loams (Fine, smectitic, frigid Glossic Natrustolls, and Pachic Vertic Argiustolls). At the time of the baseline sampling, site means for sand, silt, and clay content and soil organic carbon (C) in the surface 7.6 cm were 285, 514, 201, and 21.4 g C kg−1, respectively (Black and Tanaka 1997). Prior to establishment of the study, the site had been managed under intensive tillage and cropping with spring wheat (Triticum aestivum L.) and corn (Zea Mays L.) or left fallow for approximately 30 years (Liebig et al. 2014). The study was a strip-split plot design with three replications. Two different crop rotations were used and both were included in each experimental replicate. The two crop rotations were (1) cropfallow (C–F: spring wheat—fallow) and (2) continuous crop (CC: spring wheat—winter wheat [T. aestivum]—sunflower [Helianthus annuus L.]). All phases of each rotation were present each year and were consolidated for statistical analyses. Experimental blocks were 9 × 9 factorial blocks of three tillage (no tillage [NT], minimum tillage [MT], and conventional tillage [CT]) and three fertilizer treatments (N rates) applied as a broadcast application of ammonium nitrate (NH4NO3) in the spring of each crop year prior to tillage. In NT, the soil surface was not disturbed except at planting. Minimum tillage utilized one or two tillage passes with a sweep plow in the fall and spring. Blade width and shank spacing for the sweep plow was 66 cm, and depth of disturbance was approximately 8 cm. Conventional tillage involved use of a tandem disk and chisel plow in the fall and spring to control weeds, incorporate crop residue, and prepare the seedbed. The disk possessed 46 cm blades, which were spaced apart by 22 cm. The chisel plow had 18 cm blades attached to curved spikes, which were separated by a distance of 18 cm. The maximum depth of soil disturbance by tillage in CT was approximately 15 cm. In the C–F sequence, plots were generally not tilled in the fall following spring wheat harvest.
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All crop residue was returned to the soil following harvest, and covered >60% under NT, 30–60% under MT, and
