Heavy rains are common in Missouri and the Midwest, in particular 2019 with record rainfall in May resulting in flooding that delayed planting for quite long. Last year was abnormal and Missouri's agriculture struggled to recover from the record rainfall (see J. Quinn's article in the "Missouri Produce Growers" bulletin, June 2019). A number of vegetable growers in low areas nearby rivers lost substantial fields of sweet corn, cantaloupes and watermelons including production in high tunnels. These loses were clearly attributed to river overflow and flooding. However, less noticeable are losses to flash flooding and soil saturation due to heavy rainfall in normal years in fields with poor drainage.
A large proportion of soil planted to fruits and vegetables in Missouri are silty clay to clay loam with relative poor drainage in comparison to deep sandy soil in other specialty crops growing areas. Excess soil moisture is conducive to soil saturation, that promote root asphyxia and rotting (damping off, root rots, etc.) where pathogens such as Pythium spp, Fusarium spp, Phytophthora spp, and others can cause serious loses (Figs. 1 and 2). Planting in shallow beds with excess moisture and poor drainage due to the soil type may exacerbate the problem since plant may not die, but they will perform poorly.
Tall planting beds (12 to 15 inches) are known to reduce the detrimental effects of excess moisture and/or flooding events in specialty crops. In most cases, tall beds improve drainage decreasing long periods of root zone saturation and maintaining good air exchange for root respiration and plant growth. Furthermore, soil conditions in tall beds are less prone to soil-borne diseases. Figure 3 shows a study with tomatoes where superior plant growth is evident in tall (12 inches) compact beds under excess soil moisture in comparison to conventional (6 inches) beds. This difference in growth was reflected in similar differences in yield between the two bed heights.
Essentially, there are two types of bed forming implements. The most common ones drag and pack the soil under the metal shaper forming a shallow bed prior to laying plastic mulch. The other type is a row hipper with two disc gangs (2-3 disc each) that throw soil up to the middle leaving a raised row (Figures 4A and 4B). The disc gangs in the hipper can be moved in two ways to adjust the positions and angles of the discs for shallow or tall rows. To form a tall bed, the rear-outer discs should be lower than the front-inner disc to make a deeper furrows. Therefore, the height of the bed depend on the angles and position of the disc gangs, and the number of discs. In figure 4A, the disc gangs are positioned to form a shallow bed. In figure 4B, the disc gangs are in angle to form a raised bed/row. Once the bed is formed, it may need a roller shaper with cones on the sides to pack the soil and shape the bed if plastic mulch were to be laid down. Roller shapers with cones can be custom made to the desired bed width and height. Some farmers raise the beds in the fall to plant cover crops and promote drainage during the winter.
Adopting tall beds is expected to improve drainage and reduce soil saturation, soil-borne diseases and the overall sustainability of specialty crops farmers and industry in Missouri.
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REVISED: February 12, 2020