How does soil organic matter affect potato productivity on sandy soil?

While many studies note the positive effects of soil organic matter (SOM) on crop yields, there is limited quantitative information on the influence of increased SOM on potato (Solanum tuberosum) productivity in sandy soil. This study estimated the impact of varying SOM on potato productivity in sandy soils and explored whether nitrogen (N) mineralization served as a primary mediator. Soil from nine fields in Wisconsin (SOM range of 1.1%-3.8%) was collected for a greenhouse study. Both NH4-N and NO3-N extracted from ion strips and potentially mineralizable nitrogen (PMN) were used as the proxies for N mineralization. Linear mixed effect models indicated that fresh matter whole biomass and dry matter vine biomass were 0.45 and 0.54 times greater at 3.8% SOM compared to 1.1% SOM at an optimal soil pH of 5.2, respectively. Similarly, total N uptake in the whole and vine biomass was 0.51 and 1.0 times higher at 3.8% SOM than 1.1% SOM, respectively. While PMN demonstrated a positive correlation with SOM, it only partially mediated the effect of SOM on productivity, specifically in N uptake in the vines. However, for most productivity measures, including PMN with SOM in the models did not substantially reduce the estimated SOM effect on productivity, indicating that SOM affected productivity mostly through mechanisms other than N acquisition by plants available through mineralization of OM. The study underscored the complex interplay between SOM and potato productivity, urging further research into the multifaceted roles of SOM in sandy soils. Increasing soil organic matter (from 1.1% to 3.8%) enhanced aboveground biomass with limited impact on tuber yield. Mostly, soil pH confounded the effect of soil organic matter (SOM) on various productivity components. Potentially mineralizable nitrogen (PMN) partially mediated the relationship between SOM and N uptake in the vines. SOM increased tuber yield without PMN mediation, indicating multifaceted influences on belowground production. SOM's benefits on productivity may allow for the reduction of inputs broadly while achieving the same yield targets.