Soil Organic Carbon and Nitrogen Dynamics Under Dryland Sorghum in New Mexico

R. Ghimire, S. Salehin
New Mexico State University
Introduction
  • Sorghum is primarily grown in the semi-arid regions of the world
  • Dryland farmers in semiarid Southern High Plains typically apply 20–50 kg N ha-1 to sorghum
  • The response to applied N fertilizer on soil properties and crop production varies with soil condition, climate, and growing season precipitation in a particular year
  • We evaluated the effects of compost and four different rates of N fertilizers on soil C and N pools and crop yield in dryland sorghum production
Materials and Methods
Study site: NMSU Agricultural Science Center (ASC) Clovis, NM (34⁰35’ N, 103⁰12’ W, 1348 m elevation)
Climate and soil type: Annual rainfall: 470 mm; maximum and minimum temperatures: 22º C and 6.56º C; soil type: Olton Clay Loam (Fine, mixed, super active, thermic Aridic Paleustolls)
Treatments: Four liquid UAN rates (0, 22.4, 44.8, and 67.3 kg ha-1 (0, 20, 40, and 60 lbs acre-1) and dairy compost at 13.5 Mg ha-1 (6 tons acre-1)
Experimental design: Randomized complete block design (RCBD) with 4 replications
Study years: 2018 & 2019
Measurements: Soil inorganic N, potential carbon mineralization (PCM) and potential nitrogen mineralization (PNM) in 72 h of aerobic incubation; SOC, and total soil nitrogen (TSN) in both years. Labile organic nitrogen (LON) was also measured in soil samples collected in 2019.  
Results
 
Table 1. Inorganic N, potential nitrogen mineralization (PNM), labile organic nitrogen (LON), and total soil nitrogen (TSN) as influenced by treatments in 0–10 cm and 10–20 cm depths of soil.
 
Results
Fig. 1. Potential carbon mineralization (PCM) under different treatments in 0-10 and 10-20 cm depths of soil. The N fertilizer rates under N0, N20, N40 and N60 were 0, 22.4, 44.8, and 67.3 kg ha-1 (0, 20, 40, and 60 lbs/a), respectively.
Fig. 1. Potential carbon mineralization (PCM) under different treatments in 0-10 and 10-20 cm depths of soil. The N fertilizer rates under N0, N20, N40 and N60 were 0, 22.4, 44.8, and 67.3 kg ha-1 (0, 20, 40, and 60 lbs/a), respectively.
Discussion and Conclusion
  • The results from this two-year study show no significant improvements in soil C and N pools with an increase in N fertilizer
  • Applied fertilizers don’t contribute to grain or biomass N content directly, but an increase in mineralizable N with the higher rate of N fertilizer was positively correlated with greater grain and biomass N
  • Compost and N40 treatments provided the best response when both yield and quality components are compared
  • Because of the slow release of nutrients in dry-soils, long-term studies will reveal the benefits of compost application on soil C and N storage

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