Nitrogen Fertilization Effects on Soil Carbon and Nitrogen in a Dryland Cropping System

Abstract

No‐till (NT) increases the potential to crop more frequently in the Great Plains than with the conventional‐till (CT) crop–fallow farming system. More frequent cropping requires N input to maintain economical yields. We evaluated the effects of N fertilization on crop residue production and its subsequent effects on soil organic C (SOC) and total soil N (TSN) in a dryland NT annual cropping system. Six N rates (0, 22, 45, 67, 90, and 134 kg N ha−1) were applied to the same plots from 1984 through 1994, except 1988 when rates were reduced 50%, on a Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). Spring barley (Hordeum vulgare L.), corn (Zea mays L.), winter wheat (Triticum aestivum L.), and oat (Avena sativa L.)–pea (Lathyrus tingitanus L.) hay were grown in rotation. Crop residue production varied with crop and year. Estimated average annual aboveground residue returned to the soil (excluding hay years) was 2925, 3845, 4354, 4365, 4371, and 4615 kg ha−1, while estimated annual contributions to belowground (root) residue C were 1060, 1397, 1729, 1992, 1952, and 2031 kg C ha−1 for the above N rates, respectively. The increased amount of crop residue returned to the soil with increasing N rate resulted in increased SOC and TSN levels in the 0‐ to 7.5‐cm soil depth after 11 crops. The fraction of applied N fertilizer in the crop residue decreased with increasing N rate. Soil bulk density (Db) in the 0‐ to 7.5‐cm soil depth decreased as SOC increased. The increase in SOC with N fertilization contributes to improved soil quality and productivity, and increased efficiency of C sequestration into the soil. Carbon sequestration can be enhanced by increasing crop residue production through adequate N fertility.

Comparison of Net Global Warming Potential and Greenhouse Gas Intensity Affected by Management Practices in Two Dryland Cropping Sites

“…Our values of C sequestration rates for dryland cropping systems were within the range reported by Halvorson et al [26]. Nitrogen fertilization has been known to increase soil C sequestration compared with no N fertilization [27]. Increased C mineralization due to soil disturbance as a result of tillage, followed by reduced or absence of crop residue returned to the soil due to no N fertilization or fallow were probably the reasons for negative C sequestration rates in CTB/N1, CTB/N0, NTB/N0, and CTB-F/N0 [11] [27].…”

“…Nitrogen fertilization has been known to increase soil C sequestration compared with no N fertilization [27]. Increased C mineralization due to soil disturbance as a result of tillage, followed by reduced or absence of crop residue returned to the soil due to no N fertilization or fallow were probably the reasons for negative C sequestration rates in CTB/N1, CTB/N0, NTB/N0, and CTB-F/N0 [11] [27]. Increased C mineralization due to higher precipitation and coarser soil texture also were the possible reasons for lower C sequestration rates in Nesson Valley than Sidney, since increased CO 2 emissions in the former than the latter site have been known [17] [20].…”

Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality

“…Humus is especially rich in N, which comprises 4%-6% of soil organic matter mass. Hence, C sequestration in soil humus requires input of both N and C that exceeds the output of these elements from an ecosystem.Thus, in many cropping systems, the application of N fertilizer increases soil C sequestration through augmented plant productivity and increased return of crop residues (114,115).…”

Changes in soil carbon and nitrogen pools after shifting from conventional cereal to greenhouse vegetable production

“…Storage of soil organic carbon (SOC) and carbonate carbon (IC) in agricultural land can be influenced by management practices such as tillage, fertilizer N inputs and crop rotations (Halvorson et al, 2002;Russell et al, 2005). Optimizing fertilizer N inputs, for instance, may increase SOC content by increasing crop yields and hence the amount of residues returned to soils (Janzen et al, 1998;Halvorson et al, 1999;Huang and Sun, 2005). Excessive fertilizer N may block SOC sequestration through suppression of the microbial population or stimulation of mineralization of old native organic C (McCarty and Meisinger, 1997).…”