# Assessment of the Effects of Garlic (Allium sativum L.) Stalk Incorporation on Soil Fertility and Bacterial Biodiversity

## TL;DR

Adding garlic stalks to soil with ammonium fertilizer improves soil nutrients and bacterial diversity, with 3% being the most effective.

## Contribution

This study evaluates the impact of garlic stalk incorporation on soil properties and bacterial communities when combined with ammonium fertilizer.

## Key findings

- Adding garlic stalks increased soil potassium, magnesium, and total nitrogen but decreased nitrate levels.
- Garlic stalks increased the relative abundance of r-strategist bacteria and the soil r/K ratio.
- The 3% garlic stalk treatment maximized soil bacterial alpha diversity and improved nutrient balance.

## Abstract

The lone application of ammonium fertilizer is one of the most commonly used measures to supplement soil nutrients. At the same time, it also causes soil acidification and leads to many environmental problems, such as soil degradation and eutrophication. Garlic (Allium sativum L.) stalk (RGS) returning has been widely researched for its benefits related to soil organic carbon (SOC) and crop yields. However, few have researched the effects of the incorporation of RGS mixed with ammonium fertilizer on soil physicochemical properties and the bacterial community composition. We incubated soil with the control (N0); ammonium sulfate (AS); and ammonium sulfate combined with 1%, 2%, 3%, and 5% (rate of the dry soil weight) garlic stalk at 25 °C and 60% water-filled pore spaces (WFPS) for 67 days. We measured the soil properties before and on the last day of the experiment. The results showed that adding RGS increased the contents of soil potassium (K), magnesium (Mg), and total nitrogen (TN), but it significantly decreased soil nitrate (NO3−). In addition, adding RGS increased the relative abundance of r-strategists and the soil r/K ratio. The α diversity of soil bacteria reached the highest value with 3% treatment. Compared to AS, RGS increased the relative abundance of Firmicutes and Actinobacteria but decreased that of Proteobacteria and Acidobacteria. The function genes of Replication_and_Repair and Cell_Motility were enhanced after adding AS, while the function genes of Metabolism_of_Other_Amino_Acids, Enzyme_Families, and Metabolism were enhanced with increased RGS rates. Although SOC increased, NO3− significantly decreased with the increase in the returning levels, which could be due to the strong decreases in nitrifying bacteria with increases in RGS rates from 3% to 5%. Therefore, adding RGS at 3% is suitable for soil bacterial biodiversity and nutrient balance.