Response of soil phosphorus to fumigation in ginger production

Soil fumigation is effective to reduce ginger soil-borne diseases by killing harmful soil pathogens. However, due to their broad spectrum of killing, fumigants might also lead to detrimental effects on soil beneficial microorganisms that play critical roles in soil functions such as soil phosphorus (P) cycling. The effect of soil fumigation on soil P cycling remains largely unclear. Therefore, the purpose of this project was to study the effect of soil fumigation on soil P availability under different agricultural management practices, mainly including the combined application of fumigants and fungicides, as well as long-term repeated soil fumigation. The following research objectives will be addressed: 1). To study the response of soil phosphorus availability and ginger growth to the long-term continuous chloropicrin fumigation. 2). To determine the effects of the combined application of chloropicrin fumigant and azoxystrobin fungicide on ginger growth and phosphorus uptake. 3). To examine the variations of soil phosphorus fractions and related phosphorus enzyme activity under the combined application of chloropicrin fumigation and azoxystrobin fungicide. 4). To study research the changes in the soil microeukaryotic community and phosphorus solubilizing microorganisms caused by the combined application of chloropicrin fumigation and azoxystrobin fungicide. For objective 1, field observations were conducted in ginger fields with continuous chloropicrin (CP) fumigation for 0, 3, and 7 years to study the variation of ginger growth and soil P availability in real farmlands with different CP fumigation histories. Ginger yields, P uptake, soil P fractions, and two phosphatase (acid and alkaline phosphatase) activity were tested. After field observation, a greenhouse experiment was conducted under the control conditions for objectives 2 to 4 to study the effects of chloropicrin (CP) fumigate and (AZO) fungicide on ginger growth, soil P availability, and its microbial mechanisms. In the greenhouse experiment, CP and AZO were applied individually and in combination. We also used single and double applications of AZO to reveal the effects of the recurrent use of AZO on ginger growth and soil P availability. In this greenhouse experiment, we first wanted to understand ginger growth conditions and P uptake (Objective 2). We then went deep into the soil system to analyze soil phosphorus fractions and two different phosphatase activities (Objective 3). After clarifying the soil P availability in the soil system from objective 3, we further analyzed the soil microbial community structure, especially phosphorus solubilizing microorganisms in objective 4. We then used the soil chemical properties (such as pH and SOM) and soil microbiome (objective 4) to explain the variation of soil P availability (objective 3), and the changes in ginger growth and phosphorus uptake (objective 2).