High tunnels, though relatively new, have gained popularity over the past decade among specialty crop growers who want to extend their growing season. However, these environments can make crops vulnerable to the development of soil-borne diseases that reduce yield. This is particularly true for tomatoes, which are the most commonly grown high tunnel crop and can be highly susceptible to soil pathogens. For most field crops, rotation systems are already in place to combat a build-up of pests and pathogens. In field-grown tomatoes, for example, growers are advised to wait a period of 3 years before replanting tomato in a particular field to break the disease cycle. In high tunnels, rotation systems are more challenging to implement due to space limitations, which results in many growers employing a tomato-on-tomato system from one year to the next. This could be especially problematic for heirloom tomatoes, which are popular high tunnel tomato varieties, that are prone to accumulating species specific soil-borne pathogens.
Figure 1. Tomato fruit yield after being planted in clover vs. tomato the previous growing season.
Figure 1 shows an experiment conducted over the course of 2 growing seasons 2017/2018, where in the initial year (2017) a variety of crops were planted including clover and tomato, while in the subsequent year (2018) tomato was planted and yields were compared. As indicated in Fig. 1, when tomato is planted after tomato, yields are approximately 20% lower than if tomato is planted after clover. The increase in yield is most likely due to a change in the microbial community of the soil after being cultivated with clover. Clover, a legume, alters the physical and biological nature of the soil by recruiting rhizobacteria for nitrogen fixation as well as providing competition for other soil borne pathogens detrimental to tomato.
To combat yield decline in high tunnel tomatoes, our research at the Meigs Horticulture Farm is exploring potential crop rotations within high tunnels that allow growers to still use a high intensity tomato rotation while incorporating more plant diversity to the system. To do so, we are incorporating a companion crop within the growing season (white clover) between the rows, and a winter crop in the off-season (winter hardy kale). We are also experimenting with grafting heirloom tomatoes onto wild relatives of tomato, as well as commercial rootstocks, to increase resistance to soil pathogens and stress. The reasoning behind these treatments is to alleviate the negative effects of growing tomato year in and year out, while still maintaining yield quality and quantity. This is an ongoing experiment that will span 3 growing seasons. We will update the research results of the project in the future issue of the Vegetable Crops Hotline newsletter.
For more information, please contact wghanem@purdue.edu