Soil Organic Carbon Pools as Early Indicators for Soil Organic Matter Stock Changes under Different Tillage Practices in Inland Pacific Northwest

Abstract

Soil organic matter (SOM) is essential for sustaining soil health and crop productivity. However, changes in SOM stocks in response to agronomic practices are slow and show years later when it is too late for adjustments in management. Identifying early indicators of SOM dynamics will allow early management decisions and quick remedial action. The objectives of this study were to evaluate long-term effects of tillage intensity and timing on SOM pools and determine the most responsive SOM pools to tillage practice. Soil from a long-term (53 years) winter wheat (Triticum aestivum L.)-spring pea (Pisum sativum L.) rotation and undisturbed grass pasture (GP) in inland Pacific Northwest (iPNW) was sampled to evaluate the effect of four tillage systems [no-till (NT), disk/chisel (DT/CT), spring plow (SP), and fall plow (FP)] on soil organic carbon (SOC, proxy for SOM), total nitrogen (TN), particulate organic matter carbon (POM-C) and nitrogen (POM-N), permanganate oxidizable carbon (POXC), water extractable organic carbon (WEOC), total dissolved nitrogen (TDN), KCl-extractable nitrogen (KEN), microbial biomass carbon (MBC) and nitrogen (MBN), basal respiration (BR), carbon mineralization (Cmin), and metabolic quotient (qCO 2 ). GP had higher levels of SOC pools than cultivated treatments. On average, tillage significantly decreased SOC and TN by 28 and 26%, respectively, compared to GP. Among the cultivated soils, tillage had no significant effect on SOC and TN, except for DT/CT that had slightly higher SOC than FP (P = 0.08). On the contrary, NT and DT/CT significantly (P < 0.05) increased levels of POM-C, POM-N, POXC, WEOC, MBC, BR, Cmin, and qCO 2 over FP or SP. However, tillage did not affect TDN, MBN, and KEN. The C-pools (POM-C, POXC, MBC, WEOC, BR, and Cmin) were more strongly correlated with SOM than the N-pools (TDN, MBN, and KEN), with an exception to POM-N. Under wheat-pea rotation in the iPNW, reduced tillage systems (NT and DT/CT) have a potential to maintain or increase SOM, which can be assessed early through its physical (POM), chemical (POXC, WEOC), and microbiological (MBC, BR, Cmin) indicators. POXC and WEOC were the most sensitive indicators of tillage-induced changes in SOM dynamics.

Short-term legacy effects of feedlot manure amendments on water-extractable organic carbon in a clay loam soil profile

“…The range (0.1-3.5%) in WEOC as a fraction of total C in our soil was generally consistent with previous studies that reported that WEOC generally represents < 4% of the total C or total organic C in agricultural soils (McGill et al 1986;Zsolnay 1996;Angers et al 2006;Hamkalo and Bedernichek 2014;Benbi et al 2015;Awale et al 2017). The percentage values in our study may have been slightly underestimated at deeper depths because of increasing inorganic C. The percentage of WEOC (of total C) in SM and CM with ST bedding is 6 to 7% (Miller et al 2012), and in feedlot manure in southern Alberta it is 6% (Hao et al 2014).…”

“…Positive and significant correlations (r=0.76 to 0.80) have been reported between WEOC and total organic C in arable soils (Hamkalo and Bedernichek 2014;Haney et al 2014;Awale et al 2017). But some have reported poor correlations (r=0.24) in other arable soils (Benbi et al 2015).…”

Macronutrients in Soil and Wheat as Affected by a Long-Term Tillage and Nitrogen Fertilization in Winter Wheat–Fallow Rotation

“…Furthermore, Hedley et al [2] reported that conversion of perennial pasture over time accumulates more C in the soil than the annually cultivated pasture. The protected SOM becomes more accessible to the soil microbes, and the soil environment becomes more conducive to SOM mineralization under cropland than in undisturbed pasture, increasing the probability of C and N loses in cultivated soils [3]. The loss of nutrients becomes more severe in dryland wheat-fallow cropping systems of the PNW because fallowing keeps the soil moist in the summer which permits greater biological oxidation than would normally occur [1].…”

“…Tillage affects SOM [3], pH [4], and nutrient availability [5]. Conservation tillage, such as disc plow (DP) and sweep (SW), have shown positive effects on crop productivity.…”

Effects of Bt-cotton on biological properties of Vertisols in central India

“…Although intensive cultivation of Bt-cotton might add increased biomass to the soil, a negative C and N balance might occur due to rapid depletion of nutrients in such systems (Sarkar et al 2008;Beura & Rakshit 2011). Further, intensive cultivation under mechanized farming cause rapid changes in native ecosystems that might cause easy oxidation of soil organic C (Awale et al 2017).…”