BY GLEN HARRIS TIFTON, GA.
The fertilizer spreader truck rolls across the field spitting out a custom blend of N-P-K, secondary and micronutrients based on grid soil sampling, followed later by the sidedress rig equipped with sensors to measure plant height and greenness and apply the exact amount of additional N (and other nutrients that may be needed). Just before peak bloom, a UAV (unmanned aerial vehicle, some call them “drones”) is used to detect areas in the field that need additional N, K or P that can be variable rate and foliar fed. Sound far-fetched? Well, in Georgia, we are not quite to this point yet. However, we are a lot closer and have come a lot further than I ever thought we would since I started working with cotton 20 years ago.
It was 1995, and we were fresh off boll weevil eradication in Georgia (I still remember all the green traps, spaced close together when we had an outbreak). GMOs were something new, first Bt then Roundup Ready. We (University of Georgia) had one fertilizer recommendation on the books for a 750-pound lint per-acre yield goal. Reports of three-bale or 1,500 pound yields, which were previously unheard of, started to come in. By the year 2000, we completed research to justify increasing nitrogen rates on cotton from 60 pounds of N per acre for 750 pound per-acre yield goals to 105 pounds of N per acre for 1,500 pound per-acre yields.
Then potassium started becoming an issue. Was it because these new varieties were higher yielding? Faster fruiting? Or both? Turns out, probably both. Plus, it was discovered that potassium deficiency causes a secondary leafspot disease, which turned out to be a good indicator. Potassium rates and the effectiveness of split applications and foliar applications of K were all studied.
For the next 10 years (2000-2010), we seemed to settle in. Grid soil sampling was popular but not as much variablerate fertilizer application seemed to be happening. New fertilizer formulations and additives were introduced and tested. Urease and nitrification inhibitors for nitrogen sidedress fertilizers became popular with a number of different products competing for market share.
Then, about five years ago, things seemed to change again. This might have been due in part to a resurgence in corn and interest in making high-yielding corn in Georgia. Questions arose about using in-furrow starter fertilizers and the need for micronutrient and split applications of fertilizers. All of a sudden, it seemed like we were doing more grid soil sampling and variable-rate applications of fertilizer. This is likely due to the cost of variable-rate spreading equipment coming down and more precision ag equipment becoming standard on all new equipment. But regardless of the situation, there is no doubt there is more lime, phosphorous and potassium fertilizer being variable-rate spread on Georgia cotton. Unmanned Aerial Vehicle (UAV) projects have started, and we found that the Normalized Difference Vegetation Index (NDVI) can pick up nitrogen and potash deficiency very well but can’t tell the difference between the two at this point. Also, right now there is a serious issue of processing and interpreting the data from the UAV fast enough to make timely in-season adjustments that will put money in the producer’s pocket.
For the first time this winter during producer meetings, I received the question, “how much fertilizer does it take to make four-bale cotton?” My first thought was once four-bale yields become more common, we will look at that. Then, I realized that I said the same thing about three-bale cotton at some point in the past, so apparently the future is here, and the time is now!
We have come a long way in 20 years, and it will be exciting to see how far we’ll advance in the next 20 years.
Contact Glen Harris in Tifton, Ga., at gharris@uga.edu.