Impact of Soil Health Practices in an Irrigated Agroecosystem
- Many farms in irrigated agroecosystems that rely on a two-crop rotation of sugarbeet and barley use field preparation for furrow irrigation, and its water delivery method, degrading soil through disturbance increasing the rate of SOM loss (Hurisso et al. 2013, 2014, 2015, Liebig et al. 2004, Norton 2011).
- Lack of rotation diversity and intensive tillage due to sugarbeet crop’s economic value creates soil loss from wind erosion decreasing soil resilience (Afshar et al. 2018).
- Planting sugarbeets using strip tillage can protect sugarbeets from wind damage and reduce soil loss (Overstreet and Cattanach 2010).
- Crop research has shown that increasing the time between sugarbeet rotations by adding another annual or even perennial crop and reducing tillage can improve soil health and retain SOM (Krupinsky 2006, Hurisso et al. 2015).
Research Questions: What are the differences in soil health indicators between the conventional (CT) and minimum (MT) tillage treatments? What are the differences in soil health indicators between the two irrigation levels (full and 75% of full)? Does the current rotation’s crop affect soil health indicators?
Approach: On-station collection of soil and lab analysis of soil health indicators in each of the 36 plots.
Hypothesis1: We expect long term crop rotation in MT plots will result in greater soil health indicators than in CT plots.
Hypothesis 2: We expect differences in yield between full and deficit irrigation to decrease due to improved soil health under MT.
Basic soil properties for the site analyzed after soil collection in August 2020 include pH, EC, soil texture, clay content, bulk density, calcium carbonate, and soil classification presented as site characteristics (Table 1.) At the time of soil collection, barley was in the dry-down phase ready for harvest, while sugarbeets and edible dry bean plots were still receiving irrigation. Results are consistent with values from previous years.
Results from the study looking at long term effects of soil health practices across two tillage treatments, two irrigation levels, and three crop rotations suggests a 33% increase in SOM over a six-year period (two full rotations) based on an increase in total nitrogen in MT compared to CT practices (Figure 1). We expect organic carbon will trend with nitrogen and represent 1/3 more SOM in MT plots, but machine analysis issues affected results and samples could not be rerun before this presentation. Irrigation is the primary effect on microbial mineralization of carbon for this irrigated system (Figure 2). Higher amounts in mineralizable carbon results suggest that in deficit irrigation plots less moisture inhibited mineralization. In Figure 3, although not significant, reduced tillage is trending towards more mineralizable carbon. Mineralizable nitrogen was not significant but the data show a similar pattern to mineralizable carbon. These initial results indicate that some soil health parameters are improving with long-term implementation of minimum tillage practices and crop rotations as we hypothesized. Subsequent yield data is still being compiled.
Figure 1. Total nitrogen percent by tillage level indicates a significant effect p < alpha = 0.05 of minimum tillage compared to conventional tillage practices.
Additional data including yield analysis for cash and cover crops along with other soil data is being compiled from August through October 2020 sampling. However, our preliminary findings suggest diversification in cash crop rotations and adding annual fall cover crops after barley harvest is improving soil health parameters in the short term. Additionally, these practices create forage opportunities for livestock integration into arid irrigated agroecosystems, and soil health management practices may affect dry bean variety choice when expanding to a third cash crop in a sugarbeet-barley rotation.
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