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Late-season Fertilizer Increases Return Crop in Pecans
By Bill Goff, Monte Nesbitt, and Cathy Browne
Following some favorable reports from growers and other researchers regarding application of fertilizer in late-season, we began a series of experiments in 1999 with the following purposes:
·
To determine if
supplemental fertilizer in late season (July-October) in on-crop years would
improve quality and next year's crop. All of the experiments were done in commercial grower's orchards. We have conducted six experiments so far. Four of the experiments were in irrigated orchards, and 2 were in unirrigated orchards. Cultivars were Cape Fear and Kiowa in the irrigated orchards, and Elliott and Jubilee in the unirrigated. In most cases, the treatments were applied to trees with moderate to heavy crops in on-years. Usually, the trees had received a spring application of 75-100 lbs. N. plus other nutrients as indicated by leaf and soil sample results, and had sufficient (>2.7%) N initially and throughout the trial. Treatments were additional fertilizer in late season, at various timings and rates. Usually, a balanced fertilizer was applied, with the ratio determined by leaf and soil sample recommendations. A 16-16-16 fertilizer with 5% sulfur, 0.5 % zinc, 0.15% manganese, 0.03% boron, 0.03% iron, and 0.02 percent copper was used in most of the studies. The rate of fertilizer was determined from the N component of the fertilizer. Rates varied from 0 to 200 lbs. of late-season N, with a corresponding application of the additional nutrients provided from the mixed fertilizer. Dates of application ranged from July 1 to October 1 in the initial experiments. Since the initial experiments showed poor response to the July 1 treatments, July dates were dropped for the later experiments. In each of the experiments we harvested the nuts from individual trees to determine yield, and took a 1 pound sample from each tree to evaluate quality. From the sample we determined % #1, % #2, % #3, % reject and total % edible kernel. We also rated foliage condition and estimated percent foliage remaining on the tree in October in several experiments. Since we were concerned with potential harmful effects of the unconventional timing of the fertilizer application, we observed the trees for signs of cold damage and for delayed shuck opening. I will provide a general summary of the most important results. The first result is the effect of the treatments on nut weight, as measured by the number of nuts per pound. None of the treatments had any effect on this variable. This was as we expected since most of the applications were done late enough in the season that nut sizing was already complete before the fertilizer was applied. If the nuts had filled appreciably better in the treatments receiving late fertilizer then nut weight could have been increased in that way. But as I'll mention later effect on kernel fill was generally small and nut weight was not increased in this manner either. Effects on current season nut quality were generally small and statistically not significant, although the trend in treatment means was generally in favor of nut quality being improved by late fertilizer (Tables 1 and 2). Application of fertilizer in July resulted in a percentage of #1 kernels of only 8%, compared to almost double that percentage when the same fertilizer was applied in August, September, or October (Table 1). This result, however, was not quite statistically significant (P=.08). Since nut weight and nut quality were not appreciably affected by late-season fertilizer applications, it follows that current season yield would not be affected. The nuts are already on the trees before the applications took place, nut size was unaffected, and quality was only marginally affected. Changes in nut abortion due to treatment might change yield. We did not measure nut drop directly, but the lack of changes in yield suggest that nut drop was not appreciably affected. Generally, as with quality, current season yield was unaffected by treatments, but the means were higher in the treatments receiving late fertilizer. The major and most important effect was an increase in yield the season after the fertilizer was applied. We had a total of 8 instances where we had applied late fertilizer under controlled conditions in replicated trials the season before and measured yield the next year. In four of these 8 instances, the next season's yield was statistically higher when the late fertilizer had been applied. In the other four instances, the yield was unchanged. In some cases, the yield the following season was almost double following late fertilizer (Table 3). In an experiment where we followed yield on Cape Fear trees for three seasons, the average yield for the three years was significantly higher in the treatments receiving late fertilizer (Table 4). The condition of the foliage was significantly improved in some cases by the late fertilizer (Table 5). Perhaps improved foliage condition partially explains the increased yield the following season as better foliage should result in increased carbohydrate reserves. Regarding date of application, our results suggested that July application appeared worse regarding both nut quality and return crop than later dates. Hunter and Lewis (1942) also showed reduced nut quality from June application. June-July appears to be a poor time to apply fertilizer in pecan orchards, compared to later dates. We generally did not show any consistent or significant difference among dates of fertilizer between Aug. 1 and Oct. 1 with all showing either equal or statistically better yield the next season. Harmful effects from late fertilizer application were not seen in our experiments. No cold injury symptoms were observed on trees receiving late fertilizer. The absence of cold damage is supported by the increased yields the year following late fertilizer application. There were no differences apparent in shuck opening time or percentage. There was no increased nut drop observed, nor any other harmful effects. Any harmful effects we might have missed, if there were possibly any, were offset by beneficial effects, since yields were generally higher and quality was the same when trees received late fertilizer. Our research would support the following guidelines for growers to follow:
This approach should temper alternate bearing, and save money on unneeded fertilizer in off-crop years.
We would like to express our appreciation to Griffin L.L.C., especially to Hilton Segler, and to the Southeastern Pecan Growers Association for their support of this research through the Partners in Production program. Without that support, this research would not have been done. |
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