Granular fertilizers are frequently utilized by golf course superintendents to maintain high quality putting greens throughout many regions of the world. Typically, granular fertilizers must be watered-in because the particles may cause tip-burn, be picked up by mowers, tracked by golfers feet, disturb ball roll, and the nutrients must be dissolved to be absorbed the plants. In recent years, however, golf course superintendents have increased pressure from golfers’ to maintain greens hard and dry. Hence, an important aspect of the use of granular fertilizers is to completely disperse the applied particles with the least amount of water and before mowing occurs. If the mowers mow over or pick-up and remove the granular, the chemical composition (if coated especially), release characteristics will change and most importantly the granular fertilizer is being under-utilized and lost from the desired target area.
Although the topic of granular fertilizer pick-up following application by mowers is extremely important to the management of putting greens, to my knowledge there has been very little research conducted or published on this topic. In a 1999 study, researchers at Penn State University (Mancino et al., 1999; 1) conducted two mower loss studies looking at the loss of potassium containing ‘green grades’ fertilizers. In that study, however, they did not mow the plots until two days after treatment (2 DAT). Mancino et al. 1999, continued to mow the plots every day for up to 9 DAT. Generally, they found that the most significant mower pick up occurred at 2 DAT and that the products did differ in there loss of potassium. In practical situations, a superintendent would apply a granular fertilizer early in the morning (either following mowing or skip mowing for a day) and irrigate the greens to disperse the granulars. Then on the following morning mow the greens. Furthermore, it has been suggested that superintendents should leave the buckets off of the greens mowers for the day following to give the granulars another day to completely disperse. This, however, can cause excess clippings to lie on the canopy and will disrupt ball roll and may cause other issues if golfers walk on particles that have not completely dispersed. Mancino and Horstein (2000) reported that the loss of Nitrogen (N) from greens grades fertilizers (SGN of 100 to 140) applied to putting green turf could range from 7.5 to > 30% of the total N applied and varied from product to product.. In a literature search for this article submitted to crop science, however, I have been unsuccessful finding the methodology used in that trial (http://crop.scijournals.org/search.dtl). It may be published, however, not present in any search engines.
Therefore, the purpose of this study was to assess mower pick-up with two products under ‘real-world’ putting green conditions. Also, due to the fact that the quantification of mower pick-up of granular fertilizer following application is fairly misunderstood and little information is available to researchers on the methods best suited for trials, the second purpose of this trial was to develop an effective method to quantify mower pick-up of granular fertilizers in an effective ‘real-world’ scenario.
Materials and Methods:
This trial was conducted on a 2004 autumn seeded mature stand of ‘L-93’ creeping bentgrass maintained at 0.125 inches (one eight of an inch). The green was constructed to United State Golf Association Specifications and is located in Doylestown, PA. The green was mowed five times a week prior to this trial. Treatments were Andersons 18-9-18 Contec DG and Lebanon Homogenous 18-3-18. Plots were 4 x 5 ft and arranged in a randomized complete block design with three replications. A 5 foot alleyway was placed between the rows to allow a mower to turn without touching or disturbing other plots. It is important to note that careful attention was taken as not to step on the plots following the application and watering. The first time the plots were touched was when they were mowed on 3 July 2007. Fertilizers were applied using a shaker bottle into a 20 ft2 shaker box on the afternoon of 2 July 2007.
No rainfall or more irrigation was supplied to the plots before the mowing. At 07:15 on 3 July, 2007 the mowing of the treated plots began. In order to best mow the plot area only, a ‘clean-up’ pass was made around the edges of the plots and alleyway. This would also alleviate the possibilities of removing leaf tissue from outside the plots. The mower was washed before mowing the first plot and in between every plot. Each plot was mowed one time over in two directions. After mowing each plot, the mower was brought over to the side of the green for a ‘superintendents view rating’ This was done by two people and was done on a 0 to 100% scale where 100 = entire sample was green leaf tissue and no fertilizer, 50= half of the clippings contained fertilizer granules and 0= sample was totally fertilizer. The data for this rating are shown in the table below. Originally, we had tried to use a hand to collect all of the clippings into a plastic collection bag. We found this task extremely difficult and did not want to disperse or possibly break up any of the fertilizer particles by doing a lot of brushing with our hands. The particles appeared to be soft and possible easy to break apart. Therefore, we took a paper towel and softly wiped out the clipping of the bucket. Then weigh the bag, paper towel and clippings. The paper towel was then placed in the dehydrator with any of the lose clippings in the bag. Therefore, using forceps any remaining particles or clippings were picked out of the bags. We then could get an accurate weight and number of fertilizer particles picked up by the mower. All data were subjected to analysis of variance (ANOVA) using the SAS mixed procedure and means were separated using Fishers LSD test (P=0.05).
Within one hour from the last mowed plot, the two dehydrators (Mr. Coffee FD 5 model) were used to dry down the first two samples. One clipping sample was done at a time. Each sample was dried for 2.5 hours which I had found to be the amount of time needed to dehydrate some clippings. Following the 2.5 hours, most of the clippings and fertilizer particles fell into the bottom of the dehydrator. Using filter paper (no static) the dried materials were scooped into a weigh boat from immediate weighing. If particles were present in the dried material, the numbers of fertilizer particles were counted. All of the sampled were dried and weighed on 3 July 2007.
Results:
Data from this trial are shown in the table above. The ‘superintendents visual rating’ was done to assess the amount of particles as compared to clippings just as a superintendent would do following the application of a granular fertilizer. The Lebanon 18-3-18 Homogenous (56.7% green tissue) had significantly more fertilizer particles in the clippings, when compared to the Anderson 18-9-18 Contec DG (98.3% green tissue) and the untreated control plots (99.3% green tissue). The mean weight of dried material also indicated that the Lebanon 18-3-18 particles were picked up by the mower. The weight of the dehydrated clippings/fertilizer of the untreated control (0.1833 g) and Andersons 18-9-18 Contec DG (0.236 g) was significantly less, when compared to the Lebanon Homogenous 18-3-18 (0.688 g). It is important to note, that these amounts were extremely small due to the fact that we mowed off very little tissue due to the double mowing the day prior. Following the drying and weighing process some of the samples had visible intact granulars and were counted. There were no particles found in the samples from the untreated control and plots treated with Andersons 18-9-18 Contec DG, when compared to plots treated with Lebanon Homogenous 18-3-18 (123.7 particles).
Conclusions
This trial indicated that it is possible to subjectively and quantitatively compare fertilizers for their potential to be picked up by a mower the morning after application. Future use of this method would be useful to researchers evaluating the loss of various fertilizers and plant protection materials. This was the first time this method using the food dehydrators has been reported for the quantification of fertilizer pick-up and future work should focus on ways to improve the process.
In this study, it is important to note that the treated plots received only 0.185 inches (4.57 mm) of water from irrigation following the application of the fertilizers. That was six total turns of these Toro heads. In the Macino et al.(1) trial, the plots were irrigated with 0.25 inches (6.4 mm) from irrigation and fertilizer particles were still picked up to 9 DAT. In this trial, we did not consider the amount of water to be significant, due to the fact that on a typical day throughout many regions up to 0.20 inches of moisture may be lost from the turfgrass canopy through evapotranspiration. In this trial we also allowed for a 10 minute break between syringe cycles. There was no mention of this practice in the previous research (1). This is a common practice of golf course superintendents following an application of a granular product as it reduces the likelihood for pooling, movement of product and run-off. These multiple run irrigation cycles may also help to better disperse granular fertilizers due to the wetting and drying cycle.
In this trial, the Andersons 18-9-18 Contec DG was not picked-up by the mower on the following day, while minor amounts of the applied Lebanon Homogenous 18-3-18 was picked up in the bucket and found on the front roller, reel and bed knife upon inspection following the mowing of the plots. Differences in the fertilizer release were not observed, however, this difference may have led to an agronomic difference. In my opinion it is extremely difficult to extrapolate the amount picked up into a percentage of total pick up for numerous reasons. First, the granulars that were picked up were noticeably smaller than the average size of the ones applied, therefore, would not give an accurate assessment of the nutrient content. Secondly, the superintendents rating indicated that numerous (probably greater than 150 per plot for Lebanon Homogenous 18-3-18) particles were lodged on the front roller, bed knife and reel.
It would be impossible to quantify these particles in the early morning. One could try to replicate this study on a dry canopy, however, there are few superintendents who can afford the time of mowing a dry canopy. Therefore, it would be extremely difficult to accurately and practically determine the percent of fertilizer pick-up. One method, however, could be to assess the turfgrass response to the fertilizer (release curve) following application and determine if differences in the quality, color, growth, clipping yield and tissue test(s).
The superintendents rating, however, indicated that there were not even small pieces of the Andersons 18-9-18 Contec DG granulars in the bucket, on the front roller, reel and bed knife following the mowing of those plots. Therefore, it is highly likely that those (Andersons 18-9-18 Contec DG) particles were completely dispersed prior to the mowing on the morning following the application. Even if the particles were slightly smaller and not completely disperse, the mower would have still picked up the ones remaining in the upper canopy. This information would be extremely useful to a superintendent using granular fertilizers in warmer temperatures (due to wet-wilt and other soil physical problems with saturated greens soils), or in times of the season in which they would like to apply a light amount of water in combination with the fertilizer application.
Acknowledgements: Turfgrass Disease Solutions, LLC wishes to express appreciation to Douglas T. Linde, Ph.D for technical assistance with this project and The Andersons Inc. for support of this research.
Specifications and is located in Doylestown, PA. The green was mowed five times a week prior to this trial. Treatments were 
edges of the plots and alleyway. This would also alleviate the possibilities of removing leaf tissue from outside the plots. The mower was washed before mowing the first plot and in between every plot. Each plot was mowed one time over in two directions. After mowing each plot, the mower was brought over to the side of the green for a ‘superintendents view rating’ This was done by two people and was done on a 0 to 100% scale where 100 = entire sample was green leaf tissue and no fertilizer, 50= half of the clippings contained fertilizer granules and 0= sample was totally fertilizer. The data for this rating are shown in the table below. Originally, we had tried to use a hand to collect all of the clippings into a plastic collection bag. We found this task extremely difficult and did not want to disperse or possibly break up any of the fertilizer particles by doing a lot of brushing with our hands. The particles appeared to be soft and possible easy to break apart. Therefore, we took a paper towel and softly wiped out the clipping of the bucket. Then weigh the bag, paper towel and clippings. The paper towel was then placed in the dehydrator with any of the lose clippings in the bag. Therefore, using forceps any remaining particles or clippings were picked out of the bags. We then could get an accurate weight and number of fertilizer particles picked up by the mower. All data were subjected to analysis of variance (ANOVA) using the SAS mixed procedure and means were separated using Fishers LSD test (P=0.05).
