 Hello, I'm Dennis Delaney, Extension Specialist for Soybeans and Conservation Cropping Systems with Extension Systems at Auburn University. And I'm going to talk a little today about when to terminate cover crops to maximize soil moisture and soil residue levels at planting time. Can YUs cover crops? Of course, everybody can remember back in the Dust Bowl days or the history of it where we didn't use any cover crops, had a lot of wind and soil erosion. So erosion control, soil water quality improvement, if we get enough organic matter back in the soil, increased water infiltration, minimized nutrient losses through this erosion, all this expensive fertilizer we put out there we wanted to stay in place. And if we use legumes as a cover crop, we can get some extra nitrogen from them. But it's always a balancing act. Cover crop management and cost in time and money versus cover crop benefits. Again, the objective is not necessarily maximizing the cover crop but maximizing the benefits from the cash crop that's been followed. We just need to get the best balance of that. It's always nice to have a really deep cover crop with a lot of biomass out there. If we're going to go through all this expense of planting, it's good to get as much back out as we can. We spend a lot of money for soil fertility, adjustment of pH, seeding costs, inoculation of legumes, again, planting costs, machinery and so on. Again, we want to terminate that as late as possible to get the maximum dollar benefits back out of the cover crop after we spend all this money to get it established. I want to remember that surface soil effects are the most critical. Those are the ones that really cushion the soil surface, help capture the rainfall that's what we're planting the seed into and what often moisture and organic matter there. So the more we can leave those cover crops on top of the surface, the better off we are. There's a lot of influences that might, when we might want to terminate the cover crop, again, that would be soil temperature. Again, going back to the cash crop that we want to plant, what the soil temperature might be. The soil moisture status. It's important to remember these cover crops are living plants. A lot of them are deep rooted, particularly the grasses, and there's a whole lot of soil moisture out that won't be available to the cash crop that we want to plant into them. Weed suppression. There's some of the cover crops of olivopathy compounds. We want to manage those as much as we can. We have a cash crop that's sensitive to these olivopathy compounds. You might have to allow at least two or three weeks before planting in order for those to dissipate out. And sometimes, if we're using them again, we want to synchronize the nitrogen release from the residues according to when the crop needs it. If the crop is needed early, we may need to terminate the cover crop early. If it doesn't need it until late, we may be able to let the cover crop grow a little bit longer. And also the pest potential. We want to make sure that we don't leave a green bridge out there between the cover crop being green and then the new green seedlings coming up and things like cutworms and diseases and all kinds of other pathogens to just jump from one from the cover crop into our cash crop and destroy it. So we want to make sure we cut that green bridge at some point and have a dry residue for people to plant. We have to kind of manage these constraints too. Normally, one big advantage of the cover crop is that it keeps soil temperatures cooler in the summertime, and also it can keep it cooler in the spring. We don't necessarily want that. You just have to be patient, understand that it's going to keep soil temperatures a little cooler, but an example of cotton is waiting until it's at least 65 degrees Fahrenheit for several days at 8 o'clock in the morning in low temperatures with continued warm temperatures forecast. So again, it just pays to be patient and just know that it's going to be a little bit cooler under these cover crops. Another thing I already mentioned is these cover crops are green and growing. We've seen soil moisture depletion down to two or three feet under a good weak cover crop. So as a quote here, the title of termination is more critical as probably the expected precipitation decreases if no rain is in the forecast for the next week or two. And we haven't had rain recently. So we have an idea to go ahead and terminate that cover crop maybe a little bit earlier. And the chances are while the cover crop is dying or melting down that in the next two or three weeks we probably will get a rainfall to replace at least some of that cover crop with soil moisture usage. If it doesn't rain, then we probably wouldn't want to plant the cash crop anyway. But again, normally here in the southeast it would rain within two or three weeks. But that would plant some of that soil moisture. I'm going to mention here that as far as timing and terminating the cover crop, there's several bar graphs here. This is some of the USDA data from Kipp-Valcom. But you can see that the ride week, the amount of biomass we can get before corn planting versus the amount of biomass we can get before corn planting is simply a matter we can wait for a month or so longer to terminate that cover crop before cotton than we can before corn. Normally I like to see at least 4,000 pounds of biomass out there to consider being a good cover crop. There will be a lot of benefit to concert soil moisture later in the season. And you see before corn a lot of times it's really difficult to get that, even with wheat. It's hard to get the maximum benefit back out. Whereas with cotton, you've got another month or so where you let the cover crop grow in the spring and really maximize those benefits. I also mentioned the maximizing the nitrogen benefits, synchronizing the nitrogen release compared to when the crop needs it. And to know that the difference between some of the crops that may immobilize nitrogen like most of the grass cover crops, rye and wheat and so on will tie it up in the legumes that will tend to release it a lot easier. So if you have a crop that needs nitrogen early and the legumes will release it fairly quickly if you have a crop that needs a lot of nitrogen early the grass cover crops may need to kill them a little early than you ordinarily want to just to start that mobilization process of nitrogen. As far as the optimum kill time for the cover crop it's just like cash crops it's important to use growth stages to go by instead of just calendar date. Most of the time we want to kill these cover crops at about the bloom stage that's usually, as a general rule, the maximum biomass that we get out of them. So with grass cover crops we want to wait until they're all up into the boot stage and they're beginning to head to get that maximum biomass. Anything beyond that we're just getting the stiffening, the stem, the seed field and so on but we're really not getting much biomass beyond that stage. But if you kill too early by the calendar date you may not get that maximum biomass out either your cover crop. Again, for most annual cover crops full bloom is a maximum biomass if you want maximum residue longevity the mid-seed field usually with these cover crops particularly grass is a unit with a stiffer stem and a lot slower decay so it lasts out there a lot longer but as always you have to take into account the planting need dates of the cash crop. You don't want to delay too long and hurt the cash crop yields that's the whole idea of the system the cover crop and the cash crop system. What we find out over the years working a lot with the USDA unit here on campus and others across southeast but we find that soil carbon and crop residues are the real key to making constellation tillage work it's not just the lack of tillage but producing and conserving the cover crop residues that offers the most benefit to productivity particularly here in the southeast where there are higher soil temperatures and rainfall or getting matter breaks down pretty quickly so if you just go back into crop residues or have a minimal cover crop and kill it too early we're just not going to build up soil again matter and build up soil productivity we need to go ahead and maximize that cover crop out there to have the most benefits. As you can see in the bottom slide this has been pretty typical a lot of producers particularly 10 or 15 years ago they want to go ahead and make sure they've got the cover crop killed soil temperature warmed up but in about a month or two that leafy material is just going to break down almost completely and you will be able to see any of it left at all it's not going to be shading the soil surface as compared to an upper left it's going to be a good heavy rye cover crop it's going to be there a while all the way through the fall so we can kind of maximize the benefits of it rather than just throw money down the hole but as always mentioned in the beginning it's always a balance to add the cover crop management particularly thanks to cash crop versus the cover crop benefits thank you