Oregon's Willamette Valley produces more than 300,000 acres of grass seed crops each year. Since field burning of residual straw is limited by statute to only a fraction of the total acreage, many grass seed growers bale the straw and pile it at the borders of the fields. High cash value vegetable crops can be grown on straw bales and most grass seed production in Oregon is on poorly drained soils not well-adapted to row crop production. Utilization of straw bales for crop production would provide a use for wasted straw bales and allow production of alternative crops in areas not now suited for their production.
Highly perforated polyethylene (HPP) row covers have increased yield and earliness of several vegetable crops. In addition to increasing air and soil temperatures, row covers might slow the escape of heat and CO2 generated by decomposing bales. The objective of this study was to evaluate the effect of HPP on the growth of tomato and lettuce on straw bales under two fertilizer regimes and with two types of straw.
Methods
Tall fescue and perennial ryegrass straw, 64 bales each, were lined out in the field on March 12, 1985, with four bales per plot. Fertilizers were applied the following day. Fertilizer rates (pounds per bale) were either 0.95 ammonium nitrate, 0.66 potassium sulfate, 0.40 concentrated superphosphate, 0.75 dolomite, and 0.20 Micromax trace element mix, or the above fertilizers at one-half these rates. Fertilizers were worked into the bales with a pitchfork and watered in. A 0.1 percent solution of X-77R spreader was applied at 13 ounces per bale to aid in the wetting process. Fermentation was underway by March 18.
One 'Pikred' tomato and two 'Buttercrunch' lettuce seedlings were transplanted to each bale on April 15. The appropriate plots were then covered with HPP (Vispore 5042). The resulting eight treatments consisted of a factorial combination of two types of straw, two fertilizer regimes, and the covered vs. bare, in randomized complete block design with three replications.
Diazinon and malathion were applied at biweekly intervals until one week before the lettuce harvest. Grass sprouting on the bales was suppressed with a wiper application of glyphosate and a directed spray of fluazifop. Additional N was applied as calcium nitrate on May 23. Rates were 0.16 or 0.08 pounds per bale with the higher rate applied to the bales which received the higher rate of preplant fertilizer. Lettuce was harvested on June 3; HPP was removed on June 10. Tomatoes were harvested weekly from August 9 to October 1. Tomatoes were graded into 3 categories: No. 1 (more than 150 g), No. 2 (100 to 150 g), and No. 3 (undersized, misshapen, or slug-damaged).
Results
Lettuce. The crop suffered considerable damage from insects and slugs, but HPP very effectively decreased foliar injury (Table 1). Lettuce yield was greater on ryegrass than on fescue straw and head weight nearly doubled with the higher rate of fertilizer. Head weight increased 65 percent with HPP (Table 1). There were no significant interactions of cover, straw type, and fertilizer rate affecting lettuce yield. The increase in yield with HPP can be attributed to greatly reduced slug and insect damage, increased air and straw temperature, possible reduction in fertilizer leaching, and, possibly, increased CO2 levels.
Lettuce production on straw bales appears feasible but increased costs for pest control may be necessary. Fertilizer use will also be higher than in soil culture since the N needs for fermentation must be supplied in addition to crop requirement.
Tomato,pre-harvest. Almost all plants not protected by HPP were killed by a -1.5°C frost on May 11 and 12. Dead and injured plants were replaced on May 16. The HPP provided significant frost protection (Table 2) but all plants suffered at least slight leaf damage. At cover removal, plant vigor was greatest on ryegrass, with the higher rate of fertilizer, and with HPP (Table 2). The number of flowers present at cover removal increased with HPP but was not affected by straw type or rate of fertilizer.
Tomato, early harvests. For the first two harvests, yield of No. 1 fruit more than doubled with HPP, because of both increased number harvested and increased fruit size (Table 2). The yield of cull fruit increased more than five-fold with HPP and the yield of all grades of fruit more than four-fold. The percentage of marketable fruit (No. 1 plus No. 2) actually declined with HPP because of the greater number of cull fruit harvested from the HPP-covered bales. This high percentage of culls was related to earliness since the percentage of slug-damaged or soft-rotted fruit was unusually high early in the season but declined rapidly to more normal levels.
The total yield of early fruit increased 50 percent with the high rate of fertilizer but mean fruit weight decreased significantly, indicating excessive vegetative growth at the expense of fruit size. Greater numbers of fruit but slightly smaller fruit size occurred on ryegrass straw compared to fescue straw.
The unusually high degree of soft rot and slug damage at the early harvests appeared to be related to culture on straw bales, since concurrent plantings on bare ground and black mulch suffered very little damage. Bale fermentation temperatures (95° to 115°F) may have been insufficient to eliminate pathogens and eggs of slugs and other pests. In a similar trial in 1984, bale fermentation temperatures were much higher. Little slug damage was noted and grass sprouting on the bales was less than in 1985.
Tomato,sum of all harvests. For the entire season, straw type had no effect on fruit yield (Table 3). Mean fruit size and percentage of No. I fruit were reduced slightly by the high rate of fertilizer. The HPP cover had no effect on the number or weight of No. 1 fruit, but did increase the yield of No. 2 and No. 3 fruit, thus reducing the percentage of No. 1 fruit. The greatest total weight of marketable fruit occurred with the combination of HPP, fescue straw, and the low rate of fertilizer.
Economic analysis. Assuming a price to the grower of $5 per box of 24 heads of lettuce, the best treatment (ryegrass, high fertilizer rate, HPP) produced 1.67 marketable heads/bale for a gross of $33.50 for the plot area or $911/acre for the spacing used in the trial. A more practical bale spacing of solids beds with 3 feet between beds and four plants per bale would have produced a gross return of $4,100/acre.
Since it is difficult to compare costs and plant populations for straw bales with ground culture, it is more useful to express yields and costs on the basis of 100 bale production units. In the above example, assuming four plants/bale, the gross per 100 bales would be $70. Direct production costs for a 100 bale tomato-lettuce unit (Table 6) are estimated at $450. Thus, the return from lettuce at $5/box covered about 16 percent of production costs.
For the tomato crop, there is an additional cost of $0.10/pound for harvesting and grading. Price to the grower was assumed to be $0.40/pound for No. 1, $0.20/pound for No. 2, and no value for undersized or damaged fruit. The best treatment had a yield of 8.3 kilograms (18.3 pounds)/plant of No. I's and 2.6 kilograms (5.7 pounds)/plant of No. 2's, for a gross return of $8.44/plant. With 1 plant/bale, the return for a 100-bale unit would be $844, or $870, including the value of the lettuce for this treatment. Harvest costs for the 100-bale unit with this yield would be $240 and the total production cost, including harvest, $690. Thus, the net return would be $870 minus $690 or $180 for 100 bales. Assuming that 100 bales occupy 900 square feet, the net return would be $8,710/acre.
Without HPP, the highest yield would also have been obtained with fescue and the low rate of fertilizer for a gross return of $726/100 bales for tomatoes and no marketable lettuce. Eliminating the HPP and the reduced harvest costs would lower production costs to $635/100 bales. Net return would be $91/100 bale unit or only 51 percent of that with HPP.
Potential returns for straw bale culture are great and the technique appears to be well-suited for direct market producers. Addition of an HPP cover increased early yield and estimated return, reduced frost damage, and allowed production of a marketable crop of butterhead lettuce.
Table 1. Main effects of straw type, fertilizer rate and HPP cover on head weight and insect and slug damage of 'Buttercrunch' lettuce Treatment Mean head wt.(g) Insect/slug damageZ Fescue 246 2.7 Ryegrass 393 2.5 **Y NS Fertilizer, low 206 2.5 high 414 2.7 ** NS Bare 242 3.9 HPP 399 1.2 ** ** Z5-point scale with 0 = no damage, 4 = severe damage. Y**, NS: means differ significantly at 1% level and do not differ significantly, respectively. Table 2. Main effects of straw type, fertilizer rate, and HPP cover on frost damage, development, and early yield of 'Pikred' tomato FrostZ PlantY Flowers Weight (kg/plant) of Fruit No. 1's Treatment damage size blooming 1s 2s TotalX wt. (g) (%) _______________________________________________________________________________ Fescue 3.8 2.3 3.2 0.17 0.08 0.87 129 17.7 Ryegrass 3.6 3.3 5.0 0.21 0.11 1.27 113 10.7 NSW ** NS NS NS NS NS NS Fert., low 3.7 2.5 3.4 0.15 0.05 0.85 139 17.9 high 3.6 3.1 4.8 0.22 0.14 1.28 104 10.6 NS * NS NS NS * ** NS Bare 4.5 2.3 3.0 0.11 0.07 0.42 112 19.3 HPP 2.8 3.3 5.2 0.26 0.12 1.70 131 9.2 ** ** * ** NS ** NS * Z5 = dead plant, 3 = partial stem kill, 1 = no damage. Y5 = most vigorous, 1 = least. XIncludes undersized and damaged fruit. WNS, *, **: means do not differ significantly, and differ at 5% and 1% levels, respectively. Table 3. Effects of straw type, fertilizer rate, and HPP on yield of 'Pikred' tomato, all harvests Treatment No./plant of Yield (kg/plant) of Fruit % by number 1s 2s TotalZ 1s 2s Total wt. (g) 1s 1s+2s _____________________________________________________________________________________ Straw Fert. Cover Fescue Low Bare 33.8 13.8 63.7 7.5 1.5 11.9 188 53.5 74.0 HPP 39.0 23.4 90.7 8.3 2.6 14.8 163 42.3 67.8 High Bare 27.4 19.8 71.5 6.2 2.2 11.6 152 34.2 66.4 HPP 21.8 18.2 73.4 4.7 2.1 10.7 146 29.9 54.7 Ryegrass Low Bare 30.9 11.9 66.1 6.9 1.4 11.5 175 45.7 64.2 HPP 30.1 18.8 94.7 6.2 2.2 14.5 152 30.6 50.9 High Bare 27.4 17.3 64.0 5.7 2.0 10.1 156 42.8 69.1 HPP 24.3 24.8 88.6 5.2 2.6 12.4 138 27.4 55.8 NSY * * NS * NS * * ** Main effects Fescue 30.5 18.8 74.8 6.7 2.1 12.3 162 40.0 65.7 Ryegrass 28.2 18.1 78.4 6.0 2.0 12.1 155 36.6 60.0 NS NS NS NS NS NS NS NS NS Fert. low 33.5 16.9 78.8 7.3 1.9 13.3 170 43.0 64.2 high 25.2 20.0 74.5 5.4 2.2 11.1 148 33.6 61.5 NS NS NS NS NS NS * * NS Bare 29.9 5.7 66.6 6.6 1.8 11.4 168 44.0 68.4 HPP 28.8 21.3 86.9 6.1 2.4 13.1 150 32.5 57.3 NS ** ** NS * NS NS * ** ZIncludes undersized and damaged fruit. YNS, *, **: means do not differ significantly, and significant differences among means at 5% and 1% levels, respectively. Table 4. Estimated production costs for a 100-bale production unit on 900 square feet of ground Bale culture Ground culture Straw bales $300 $ 0 Fertilizer 60 40 Row covers 15 15 TransplantsZ 20 20 Other fixed costsY 55 75 Total $450 $150 ZAssumes 1 tomato and 4 lettuce plants/bale. YIncludes land rental, irrigation, labor other than harvests, pesticides, and ground preparation (not necessary with straw bales).