Soil Health Under Annual Vs. Perennial Crops in Central Iowa.

Biofuels derived from crops serve as potential substitutes for fossil fuels in the US and around the world. In 2008, Iowa State University established a long-term, large-scale, randomized complete block design experiment to compare biofuel cropping systems: continuous corn (CC), continuous corn with rye cover crop (CCW), unfertilized reconstructed prairie (P), and fertilized reconstructed prairie (PF). In this presentation, we describe the impacts of these annual and perennial crops on soil health parameters as assessed in 2016.

We collected surface horizon (0-15 cm) composite soil samples before planting (in April) and after harvest (in November), and we measured several soil health indices: Potential soil CO₂ respiration using the Solvita technique, water-extractable organic carbon (WEOC) and organic nitrogen (WEON), and key nutrients (P, K, and Ca) extracted with both a mixture of weak acid salts (H3A extractant) and the Mehlich-3 extractant.

Among the cropping systems, potential soil CO₂ respiration ranged from ~80 to ~155 mg CO₂-C kg^-1, and potential respiration was greater in the perennial systems than in the annual systems. Compared with its concentration under the annual crops, WEOC was also greater in the perennial PF and P cropping systems than in the annual systems.

Phosphorus extractable by the H3A solution was typically about 2/3 that extractable by the Mehlich 3 solution. The H3A-extractable P was the lowest under PF and P both before planting and after harvest, and this was similar to the pattern for Mehlich 3-extractable P. For all of the cropping systems, the H3A solution extracted ~8-9 times less Ca and 5 – 8 times less K than the Mehlich 3 extractant.

The Haney soil health index values (an index that combined CO₂ respiration, WEOC, and WEON measurements) of the perennial cropping systems (PF and P) were larger than those of the annual cropping systems (CC and CCW). There was no consistent pattern to the soil health index values before and after planting in these Iowa Mollisols.