Thirty‐Year Crop Rotations and Management Practices Effects on Soil and Amino Nitrogen

Abstract

AbstractMethods of assessing how agronomic practices influence soil productivity and sustainability are required. The effects of various agronomic practices on soil organic N and hydrolyzable amino N in a Udic Haploboroll were determined in a long‐term (30‐yr) crop rotation study at Indian Head, Saskatchewan. Practices assessed included fertilization, fallowing frequency, green manuring, and inclusion of a grass‐legume forage crop in predominantly spring wheat (Triticum aestivum L.) systems. Fertilization, green manuring, or inclusion of a grass‐legume hay crop significantly (P < 0.10) increased soil and amino N (amino acid N plus amino sugar N), particularly as fallowing frequency was reduced. When the relative molar distribution of the amino acids was used to assess changes in soil organic‐N quality, significant and consistent increases in aspartic acid and decreases in arginine and leucine were observed; however, the differences were mainly associated with the 6‐yr mixed and fertilized continuous wheat (Cont W) rotations. Comparison of our N‐concentration results with an estimate of the initial (1958) N concentration suggests that all fallow‐containing monoculture wheat rotations and unfertilized Cont W have failed to maintain soil N, the unfertilized 3‐yr legume green manure‐wheat‐wheat system has maintained soil N, while the 6‐yr fallow‐cereal‐hay (grass‐legume) and fertilized Cont W systems have increased soil N. Hydrolyzable amino N was only marginally more effective than Kjeldahl N for describing changes in soil organic‐matter quality.