Solarization and Living Mulch to Optimize Low-Input Production Systems for Small Fruits (88-87-4)
Disease, insect and weed pressures can be major limiting factors to successful fruit production in the South. Production of most horticultural crops in the South is chemical and labor-intensive. Some fruit crops like blueberries and strawberries, however, may lend themselves to alternative farming systems. For blueberries, disease and insect pressures are minimal. The crop could be grown free of chemical inputs if suitable management alternatives to soil fertility and weed controls were available. One alternative is the use of living mulches. By proper selection of living mulch cover crops, weed competition could be eliminated through both a smothering of the weeds and an allelopathic effect. Nutrient inputs could also be supplied by the decomposing mulch.
Strawberry yield was not affected by soil solarization relative to the control or soil fumigated plots. Yields in all soil treatments were high with 29700 kg fresh berry/ha. Manured plots (44800 kg manure/ha) produced an additional 8000 kg fresh berry/ha compared to control plots. Use of green manure or chicken manure alone or in combination produced yields equivalent to the use of commercial N fertilization.
Solarization for Strawberry Production
With soil solarization, sustainable annual strawberry production in the South was obtained. If done correctly, solarization may be an adequate fumigation substitute for controlling soil-borne pests, such as weeds and nematodes. It is not, however, a fail-safe alternative to fumigation. Solarization will not be effective at sites that are plagued with extremely high populations of pathogenic nematodes or difficult to control perennial weeds, like nutsedge. Solarization plastic must be applied at the correct time of year to maximize solar heating. It is most effective during the hottest part of the summer with the longest day lengths. We have also encountered other problems with the use of solarization, such as obtaining the appropriate type of plastic. Under our solarization system, the plastic must last at least one year in the field. This allows for the plastic to be in the field 2 months for solarization, sprayed white and planted with strawberries and then replanted with a vegetable crop the following summer. Several of our initial attempts at solarization were not successful because the plastic lasted only 4 to 5 weeks. Obtaining clear plastic with sufficient UV protection to last a year is currently difficult on short notice.
To be completely sustainable, alternative inputs of nitrogen into the soil must be done prior to solarization. The use of either a combination of both winter and summer legume green manure, manuring followed by a nonlegume cover crop, or direct manure applications prior to solarization provided yields equivalent to use of commercial N fertilization at Overton. Adequate biomass must be produced by the cover crop or enough manure added to supply the nutrient requirements of the desired crop. Two successive, well established crops of legumes were able to satisfactorily meet the needs of the strawberry crop at Overton. In Lubbock and Poplarville cover crop use as a green manure was not as successful. Timing of planting after green manuring and inadequate cover crop production (single crop vs two crop rotation) contributed to the poor response at these locations.
The remaining limiting factor for a complete “organic” production system under a solarization/manure scenario would be the control of fruit rots. This last season, extremely heavy rains during harvest season (>16 inches) caused some cullage (10-15%) due to fruit rots. No sprays were used to control decay. We felt that this level of loss due to decay, although double the amount from the previous year, was acceptable. Decay levels were not significant enough to make fungicide applications an absolute necessity for the system.
Economics for using solarization appear comparable to that of fumigation without the environmental hazards, and significantly better than not treating the soil at all. The Economics of this system, could be improved by double cropping (following strawberries with cantaloupes on the same plastic). Cost for the low-input system will depend on which nutrient input option is used. Yields for each nutrient input options have not been evaluated yet. A solarization + manure system would cost $260 less per acre than fumigation + conventional fertilization, and only $75 more than the use of just black plastic alone. If conservative yield and price values are used and there is no differential in price received for fruit, our data for the last 2 years indicates that the conventional system is 25% more profitable than the low-input solarization system. At a 10% price differential between “organic” and conventional fruit there is no difference in net return between the systems; at a 20% differential the solarization system has a 20% greater return. The solarization system was always more profitable than the system which had no soil treatment. In the short run, the use of solarization would only be monetarily expedient for growers who could capitalize on the organic market niche or who did not have access to fumigation equipment. As with most low-input sustainable systems, however, the major monetary benefits are hidden in the long term increases in land productivity.
Blueberry Living Mulches
When the efficacy of living mulch systems for blueberries was evaluated by Kim Patten and his colleagues in growers’ fields in Texas and Georgia, rye and annual rye grass resulted in the highest mulch production and most consistent stands of mulch crops in the winter. In producing blueberries, it is absolutely essential to have a ground cover or a mulch, to protect the plants in the winter. This is a very expensive operation when farmers buy and distribute straw or some other kind of mulch in their blueberry fields.
Farmers in this project are growing their own mulch right in the fields. Pearl millet was the most successful cover in the summer. Crimson clover was the only legume tested that was found to be suitable for a living mulch crop. Several crops, especially pearl millet, exhibited allelopathic weed control. The estimated cost of using cover crops twice a year for living mulch is $130 per acre for blueberries, approximately the same cost encountered with the conventional blueberry fertilizer and herbicide program. However, the living mulch provides many advantages farmers don’t get from chemicals — advantages that are being tested over several years to protect growers against false “successes” that may fail after a year or two.
(1) Investigate the feasibility of eliminating fertilizer and herbicide input on blueberries grown in the South through the use of a combination of legumes and annual summer forage crops as living mulch systems.
(2) Evaluate solarization as a replacement for fumigation and cover crop production as a replacement for synthetic chemical herbicides and fertilizers in growing strawberries.