"You can't come back from wet, you can come back from dry, but not wet." A very good agronomist and trusted consultant, Joel Simmons, gave me this advice last fall. Not only do I believe in this principle, but I think it may be the most important principle with respect to managing low-cut bent-grass through hot/humid conditions.
USGA greens are built on sand so that the green will: (1) drain well; (2) resist compaction and (3) provide a nice balance between air and water porosity. In other words, USGA greens are designed o hold just enough water to achieve field capacity, but not enough water to remain saturated for extended periods.
Saturated soil adversely affects grass by increasing heat retention, reducing gas exchange and most importantly, by minimizing the amount of oxygen that otherwise may reside in the pore space of the profile.
Heat retention occurs because water is denser than air so when it heats up, it stays hotter longer. When wet soil stays hot for an extended period of time, scald occurs. In putting greens, you typically do not see the scald damage at the canopy/crown level because infiltration rates help water get past the surface. However, in profiles that hold moisture, or in areas of greens that remain wet (low-lying areas), the scald occurs within the root-zone. Once the roots go, the leafy tissue above ground is sure to follow suit.
Although scald is a major concern, the deprivation of oxygen may be tantamount to a green's failure/survival during hot/humid stretches of the summer. Oxygen assists the plant in metabolizing food. For example, in the absence of oxygen, the plant struggles to trans-locate magnesium. As an essential component of chlorophyll, the reduction in usable magnesium leads to a decrease in photosynthesis which in turn results in a reduction of structural carbohydrates. Without carbohydrates, the plant can't build parts and decline ensues.
So, between heat retention and the deprivation of oxygen, water management becomes extremely important to the success of bent grass putting greens. Although, irrigation systems have become even more sophisticated, they remain fairly indiscriminate in terms of where water is or is not applied. For example, say that I have a green that stays very dry on the front crown, but very wet in a low-lying swale. Over-head irrigation may be ideal for the dry crown area, but may lead to over-saturation in the back of the green. Going back to the opening quote, "we can always come back from dry." In other words, in this situation, we choose to manage the green with daily hand-watering so that the crown stays hydrated while the low-lying area can dry down properly. In this way, we micro-manage the surface so that no area stays too wet.
This management style is widely adopted by the turf industry and although strides have been made in areas like wetting agents, irrigation control, fans and sub-air, I am not sure we will ever see the day that hand-watering is not an integral part of any successful turf management program.
Typically, we spend the morning checking the moisture levels of the greens. We have established thresholds and if the moisture is below those thresholds, we water those specific areas. We prefer the morning hours because the heat of the day isn't on top of us and by mid-afternoon, the applied water has had a chance to drain off. In the afternoon, we check the greens for active wilt and apply water where obvious wilt symptoms are occurring.
The last sentence brings us to the main point of this post. We recognize that employees hand-watering in the middle of the day can be a nuisance. As such, we try very hard to stay out of the way, work in backwards rotations and appreciate the golf experience of every member and guest. However, to maintain the greens as dry as possible, in an attempt to enhance play ability and practice good agronomy, we must hand water throughout the day. It is a necessary evil for the summer months.