What soil ecosystem services and economic benefits does 50 years of no-till provide in contrast to other tillage practices in Southern Illinois?

No-till increased large aggregates in size 1-2 mm (Fig. 1), whereas CD did so below 0.5 mm. No-till also increased aggregate associated C and N (Fig. 2) relative to all other treatments in small and large aggregate sizes, and additionally increased C, N and POXC (Fig. 3) relative to all other tillage treatments at the 5 cm depth. We concluded that NT provides a more stable soil system (Fig. 4) and was able to maintain or increase aggregate associated C, N and POXC given environmental stresses such as intense rainfall that could cause erosion, nutrient runoff, soil crusting, drought stress, etc.

Additionally, long-term NT practices increased SOC and POXC greatly at 0-5 cm soil depth and total soil C percentage in the top 15 cm (Fig. 5). At depths from 15-90 cm, 50 years of NT did not build total soil C. Therefore, additional practices to incorporate or deepen soil C could be beneficial (specific practices are discussed below).

After long-term maintenance of NT and CD, soil moisture and temperature only differed early in the growing season (~1.5 months after planting). Soil temperature was only lowered by 6% in the NT plots compared to the soil warming effects of CD. However, the soil volumetric water content (VWC%) was increased by 38% in the NT plots. Although these differences become insignificant later in the growing season, there is an advantage of early planting when using CD in overly wet conditions. Conversely, global warming trends are causing the common issue of extremes of both wet and dry, cold and hot. In these conditions NT having a higher VWC could be an advantage during sudden drought early in the season, or a disadvantage when early rains are too abundant.

Moreover, NT reduced both wet and oven dry bulk density by 8% compared to MP and CD on the surface, compaction at 10 cm was the lowest under the influence of a moldboard plow, with the greatest compaction under NT. This pattern continued at 20 cm, but at 30 cm NT was 30% less compacted. Our infiltration measurements were not affected by tillage. Therefore, even after 50 years without tilling, the physical benefits below the soil surface are limited and could be improved. To further build SOC and total C over depth, while reducing bulk density and improving infiltration, integrated management practices including over-wintering cover crops with extensive root systems such as annual rye grass (Lolium perenne L. spp. multiflorum) or winter cereal rye (Secale cereal L.) is needed (with caution for herbicide resistance problems). Our recommendation of building SOC over depth through overwintering cover crops is in agreement with previous recommendations from different climatic conditions: in Illinois under Aquic Argiudolls (Villamil et al., 2006), in Georgia under Orthic Luvisols (Sainju et al., 2002) and Rhodic Kandiudults (Sainju et al., 2003), and in central Italy under Typic Xerofluvents (Mazzoncini et al., 2011).

Over the course of three years (2018-2020) cumulative nitrous oxide gas emissions, a greenhouse gas that is 300x times more polluting per lb than carbon dioxide, were dramatically increased by fertilization and minutely increased by CD compared to NT. However, when those emissions were scaled with yield (g N₂O-N Mg^-1 grain yield), long-term no-till practices almost half the amount of nitrous oxide emissions compared to CD. Therefore, farmers can reduce their greenhouse gas emissions by maintaining NT rather than CD, despite fertility practices.  Additionally, in N0₃-N and moisture (Fig. 6) were the main drivers of nitrous oxide emissions while the presence of gram negative bacteria and the Summed Maturity Index (ΣMI) were negatively related to emissions. Gram negative bacteria are known to be nitrogen fixing and in turn reduce emissions and a high summed MI (1-5) indicates a more stable soil system rather than a boom and bust soil system.

Year had a greater influence on N balances then tillage did. Although we had an idea that as root surface area increased with a reduction in compaction caused by tillage effect, yield and therefore N balances would increase nutrient availability, balances were unchanged statistically by long-term tillage in both soy and corn. Additionally, after 50 years of tillage effects, yield was unchanged from tillage to tillage.

Soil ammonium (NH₄-N) was unchanged by tillage treatments. However, soil nitrate (NO₃-N) under CD was increased by 360% in NT during one warm and wet sampling in August due to an increase in nitrification. Other than this change, it appears that NT and CD, after fertilization and planting, do not have an overall effect on N-release in the soil.

After forty-nine years of different tillage treatments, soil properties had also differed enough that nematode assemblages (total community analysis) had separated into distinct populations, but still remained statistically insignificant. Surprisingly, MP and NT had significantly higher nematode structure index (SI) than AT. This suggests that these tillage treatments, by the fall, had a food web state that was least affected by stress or disturbance. It appears as though the continuous maintenance of NT, aggregate stability and organic matter accumulation that is associated with NT was identified with a high SI; however, the yearly aeration of CT seems to have benefited the food web after an entire growing season to allow the stress effect of tillage to reduce (fall nematode soil sampling).

Phospholipid fatty acid analysis concluded that NT promoted gram positive bacteria. These bacteria are commonly encouraged by complexity of soil C and a higher level of microbial active carbon in the soil; thus, we can assume these attributes are occurring most in the NT treatment. Additionally, enzymatic activity was stimulated by NT, specifically arylsulfatase. This enzyme is commonly found in soils with consistent soil moisture and accounts for more than 50% of the total activity of soil microbial biomass.

Overall, NT had the greatest positive effect on physical, chemical, and biological characteristics in the soil over the long term. Tillage, even periodically like in AT, appears to retard the development of positive effects seen by reducing tillage intensity in NT. Alternate tillage (2-yr of NT followed by a MP) offered some improvements in aggregation size and stability compared to continuous MP, but did not significantly increase yield compared to NT. Therefore, practicing NT and periodically deep-tilling, when it is deemed necessary by the producer, can be as detrimental to soil physical properties as yearly reduced tillage, but not biological. Added benefits of NT also include a large reduction in greenhouse gas emissions and reduction of farm time and labor in addition to soil biological health from even CD. However, the differences in soil physical, chemical, and biological properties do not necessarily translate to higher corn yield in any given year due to variability in soil moisture and temperature early in the growing season. Thus, we can conclude that if farmers would like to continuously NT there will be more soil and ecological benefits than economical drawbacks.