Carbon and Nitrogen Pools of Southern High Plains Cropland and Grassland Soils

Abstract

Soil C and N have long been recognized as important indicators of soil productivity. The current low levels of soil C and N of cropland soils have led to interest in sequestering C with reduced tillage cropping systems and the Conservation Reserve Program (CRP). Our objective was to assess agroecosystem effects on soil C and N pools in the Southern High Plains. The agroecosystems included three cotton ( Gossypium hirsutum L.) cropping systems, CRP land, and native rangeland (NR). We sampled 0‐ to 5‐, 5‐ to 10‐, 10‐ to 15‐, and 15‐ to 30‐cm soil depths at 12 farm sites in five counties in West Texas. Total soil C and N, particulate organic matter (POM) C and N, natural abundance of carbon‐13 isotope (δ 13 C) of POM and of whole soil, potentially mineralizable C and N, water‐extractable carbon (WEC), and extractable ammonium (NH + 4 ) and nitrate (NO − 3 ) were determined. Total C and N in the 0‐ to 30‐cm soil profile were 34 Mg C ha −1 and 2.5 Mg N ha −1 for NR, and 23 Mg C ha −1 and 1.9 Mg N ha −1 for cropland systems, respectively. Total soil C and N in CRP land were greater in cropland soils only in the 0‐ to 5‐cm layer, and were 24 Mg C ha −1 and 2.1 Mg N ha −1 in 0 to 30 cm. Labile C and N pools were positively correlated with each other and with total soil C and N. Low soil test P may have limited C and N sequestration in CRP land and NR. Improved management practices are needed to sequester C and N in CRP and conservation‐tillage cotton systems in the Southern High Plains.