Thirty-year amendment of horse manure and chemical fertilizer on the availability of micronutrients at the aggregate scale in black soil.

The research focuses on the impact of thirty years’ use of horse manure and chemical fertilizers on micronutrient content and availability in crops grown in black soil.

Introduction and Methodology

• The research involved an extensive study of seven different crop treatments. These treatments included three standard fertilization methods: application of nitrogen and phosphorus (NP), the application of horse manure (M), and a combination of NP and horse manure (NPM). Alongside these, there were three experimental treatments using the same fertilization types but at double the normal rate (N2P2, M2, and N2P2M2).
• A “CK” treatment was also included, which presumably was a control group.
• Soil samples were collected and divided into four different categories of aggregate size, the division process being carried out via a method known as wet-sieving.
• Corn crops were grown using each treatment, with samples gathered and analyzed.

Results

• Within the soil, the double rate fertilization NP treatment (N2P2) massively increased the detectable levels of Iron (Fe), Manganese (Mn), and Copper (Cu), with increases of 732%, 388%, and 42% respectively compared with the control group.
• Contrastingly, doubling the application of horse manure (M2) reduced the levels of the same elements by 26%, 22%, and 10% respectively compared to the control.
• Zinc (Zn) levels within the soil, and also within the corn crops, were found to be higher in both treatments that included horse manure (M and M2) than other treatments studied.
• The Zn levels in the soil were noted to have a significant relationship to soil organic carbon (SOC) levels in particular aggregate groupings.
• Manganese concentrations in corn stalks and grain demonstrated a clear correlation with the detectable Mn levels within the soil and specifically within the smaller microaggregates.
• Zn levels within the corn stalks appeared linked to the concentrations of the element detected within bulk soil, microaggregates, and larger macroaggregates.

Conclusions

• Long-term use of horse manure as a fertilizer could increase the availability of Zn within the soil and consequently its uptake by corn crops. The study postulates this could be due to the presence of soil organic carbon acting to ‘activate’ the Zn.
• Conversely, the application of chemical fertilizers appeared to increase detectable Fe, Mn, and Cu levels within the soil by reducing soil pH levels.
• The results also imply that Mn uptake by corn crops is most likely to originate from smaller microaggregates of soil, whereas Zn within the crops appears to come primarily from larger aggregates.