小白菜的贮藏.doc

小白菜的贮藏
更新时间：2003-9-19 　　来源：中国蔬菜网

最适储存温度：0℃

相对湿度：98%RH以上。

采收后应尽快预冷。其最佳的储存条件为冰点以上，0℃左右、98～100%RH，约可存放两周。储存温度高，菜叶易黄化及腐烂，储存寿命较短。

储存温度（℃） 0 5 10 15 常温（20℃）
储存期限（天） 15-25 8-10 6-8 3-5 1
大白菜的贮藏
更新时间：2003-9-19 　　来源：中国蔬菜网

最适储存温度：0℃

相对湿度：98%RH以上

结球白菜最佳的储存条件为0℃，95-100%RH，约可储存1.5-2个月。采收时受伤的白菜及病叶必须去除，储存环境中不可有乙烯存在。1%的低氧储存可以延长其储存期限。

储存温度（℃） 0 5 10 15 常温（25℃）
储存期限（天） 40-70 30-50 15-30 10-20 4-10
大白菜采后处理
更新时间：2003-9-12 　　来源：edis

Handling Florida Vegetables: Cabbage 1

Steve Sargent2

Cabbage is grown in Florida under a wide variety of conditions but best quality is obtained during the cooler season of fall/winter/spring. Cabbage production in Florida is intended for the fresh market in those areas of the U.S. unable to produce cabbage during the late fall/winter/spring. This publication is intended to assist the vegetable-handling industry to provide high quality fresh cabbage that is available, desirable, and nutritious for the consuming public.

Preplant Fertilizer
Starter fertilizer. Current recommendations are only a fraction of the total seasonal fertilizer requirement, either liquid or dry, be applied in the bed as a starter fertilizer for drip irrigated crops. This starter fertilizer would contain all of the phosphorus (P) and micronutrients and up to 40% of the nitrogen (N) and potassium (K). On soils testing very low in P and K, the starter can be broadcast or banded in the bed. If only small amounts of P and micronutirents are required, then it is normally better to band these materials. Bands should be placed below the bed surface 2 to 4 inches and to the side of the plant row, but not between the drip tube and row. In most cropping situations, approximately 30-40 lb/acre of N and K would be sufficient in the starter fertilizer mixture. The amounts of P and micronutrients should be determined by a calibrated soil test. In situations where the soil test index for P is high to very high, then no P is required in the fertilizer.
Phosphorus and micronutrients. In general, P and micronutrients are not recommended for simultaneous application in drip irrigation systems in Florida. This is because of the possibility of precipitation of P and micronutrients or the P and calcium or magnesium in the well water. Research has shown that P can be successfully applied through drip irrigation systems with certain precautions (Rolston et al., 1981; Mikkelsen, 1989). However, if application of P is required during the season (such as during cold periods), it should be injected alone. Acidification of the irrigation water to pH 4.0 to 5.0 might be needed to keep the P in solution during application, especially when using the high pH water from the Floridan aquifer. Acidification can be achieved by using phosphoric, sulfuric, hydrochloric, or other acids to reduce the pH of the water. In summary, injection of P is possible and can be an efficient method of P application, however injection must be done with careful attention to water pH and is generally not recommended for Florida vegetables.

Caution: When acids must be diluted with water, always pour the acid into the container of water. Never pour water into acid because it will splatter when it contacts the acid.

Micronutrient injection can present problems similar to those experienced with P injection. The key is to avoid precipitation events. Potential problems with micronutrients are less severe compared to P because rates of application are normally much less with micronutrients than P. If micronutrients must be injected, then soluble forms, less subject to precipitation, such as chelates, should be used. Like P, micronutrients should be injected alone to avoid potential precipitation problems.

Although there are serious problems and considerations with injecting P and micronutrients, there are several potential benefits from proper injection where water chemistry is suitable. Phosphorus and most micronutrients are relatively immobile in the soil so that generally only one or two applications are needed in a growing season. Also, in most Florida vegetable soils, only small amounts are needed. Research has shown that plant recovery of these nutrients can be increased when they are applied through the drip system (Rolston et al., 1981; Mikkelsen, 1989). This is probably due to resulting "band-like" application in the drip-irrigated zone where the nutrients are not widely mixed with the soil where fixation can occur. Although only a portion of the root zone would be exposed to the nutrients, research shows that not all of the root system needs to absorb the nutrient to benefit the plant.

There have been some serious clogging problems in Florida from improperly managed P and micronutrient injections. This is why injecting P and micronutrients is not often practiced. If injections are required, proper procedures should be followed.

Zero in-bed (preplant fertilizer). In some production systems where soils are relatively high in organic matter, micronutrients, P, and K, it is possible to grow successful crops with no in-bed fertilizer ( i.e. all fertilizer (nitrogen) applied through the drip-irrigation system). This is particularly attractive for areas in the state where growers experience soluble salt problems in the soils. Reducing the amount of dry fertilizer applied in the bed could potentially reduce soluble salt injury to young seedlings or transplants. The use of soluble N and P starter solutions with the transplants might still be advantageous but these amounts of N and P are very small.

Slow-release. For some crops such as strawberries, tomatoes, and peppers, benefit can be achieved from using slow-release fertilizers in the in-bed starter fertilizer mixture to provide an early season N supply. Slow-release fertilizers are less subject to leaching during the early part of the season when the beds are wetted with subirrigation. Also, slow-release fertilizers have a lower salt index so they are less likely to damage young seedlings and transplants early in the season (Everett, 1977). Supplying 30-40 lb/acre of N from slow-release fertilizer, although more expensive, might be beneficial for these crops. It is important to select a slow-release fertilizer with a nutrient-release pattern appropriate for supplying N to the young crop. This practice is more important for fall crops when frequent rain reduces the need for irrigation, yet fertilizer is still required by the young crop.

Preplant fertilizer. Since preplant fertilizer is applied in small amounts, the most efficient application method is to band the fertilizer near the plant row. The fertilizer can be banded in the bed as dry or liquid material as the bed is formed and pressed. Incorporation of fertilizer by mixing it throughout the bed is acceptable if it will not be exposed to leaching or drying out.

Any fertilizer placed in the bed before planting should be placed so that it will be least likely to leach, either from rain coming through the holes in the plastic or from water applied with the drip irrigation tubing. This means that fertilizer applied in bands should be applied to the area of the bed outside of the tubing placement. The band should not be placed on the surface between the tubing and the row because irrigation water from the tubing would have a tendency to move the fertilizer salts toward the plant where soluble salt injury could occur.

Fertilizer bands should not be placed on the surface of the bed because they may dry out as the surface of the bed dries when the water table is lowered. Banded fertilizer should be placed 2 to 4 inches deep in the bed where it will remain in contact with moist soil, dissolve, and be available to the plants. In-bed fertilizer materials can use many fertilizer sources. Materials such as triple-superphosphate, ammonium nitrate, potassium chloride, and potassium nitrate have worked well as starter fertilizers.

After preplant fertilization, the remaining 60 to 80% of the N and K is applied in increments through the cropping season via the drip irrigation system. In some cases, growers apply some of this N and K in bands ("hot-mix") on the surface of the bed. These growers feel they need a certain amount of fertilizer in the bands for rainy periods when they do not need to irrigate with the drip irrigation system. In most situations, hot-bands are not needed, and most often the fertilizer material in the hot-bands is not fully utilized by the crop (Figure 8) . This is because, in many cases, the hot-bands dry out after the water table is lowered, especially in the shoulder area. A significant amount of the N and K fertilizer in these hot-bands is then not available to the crop. If drip irrigation is being used for the injection of fertilizer materials, it is best to use the system to its fullest extent. This means injecting 60 to 80% of the N and K through the system.

(Figure 8) .

Injected Fertilizer
Rates. On typical Florida sandy soils, in most situations injected fertilizers will consist only of N and K. The amount of N to use is determined by the crop nutrient requirement for N for that particular crop. This amount of N is recommended for each crop for each season. Specific recommendations for each crop are presented in SP 177 (Hochmuth and Hanlon, 1995) and in this publication for drip-irrigated crops. Recommendations are under continual revision as more research results become available.
The K amount to be injected is based on the soil test predicted amount of K required for the crop minus the amount that is applied in the bed preplant. For example, if the soil tested medium in K, perhaps only 100 lb of K 2 O fertilizer would be required for the season. If 20% of this K 2 O ( i.e. 20 lb) were applied in the bed as starter fertilizer, then 80 lb would be injected through the season.

Sources. There are several sources of N and K that can be used for drip irrigation injection (Locascio et al., 1978; Locascio and Fiskell, 1979; Locascio et al., 1981a; Locascio et al., 1982; Fiskell and Locascio, 1983; Locascio et al., 1984; Locascio and Martin, 1985). All sources must be highly water soluble to be effective for drip irrigation injection. Nitrogen sources including ammonium nitrate, calcium nitrate, various nitrogen solutions, and potassium nitrate can be used to supply the N. Potassium sources include potassium nitrate, potassium sulfate, or potassium chloride. Chlorides from potassium chloride should not be a problem where soil-test recommended amounts of K are not exceeded.

The ratio of N to K is not important for vegetables. As long as the soil test predicted amounts of N and K are added, then the crop nutrient requirements will be satisfied. If some sort of ratio theory such as 2 K to 1 N ratio is practiced, then overfertilization with K is likely. For example, if 175 lb of N is required by a tomato crop, then 350 lb of K 2 O would be applied by using this 2:1 K:N ratio theory. Recent research with tomatoes and peppers has shown that equal crop yields and equal crop quality are achieved with various ratios of K to N ranging from 1 N to 3 K through 3 N to 1 K. It should be noted that as the ratios change, so do the rates. Therefore it is impossible to separate a rate effect from a ratio effect. Furthermore, in situations where the soil tests medium or above in K, specific ratio of K to N fertilizer would have little impact once that fertilizer is mixed with the soil which already contains large amounts of K.

A portion, approximately 25 to 50% of the N, should be applied in the nitrate form, especially for crops planted in cool soil conditions. For crops planted in warm seasons, the bulk of the N (75%) can be supplied from the ammoniacal form. Plants can absorb and utilize appreciable quantities of ammoniacal N. In addition, under warm soil conditions, the ammoniacal form of N is rapidly converted by nitrification to the nitrate form. The ammoniacal form of fertilizer is less expensive than nitrate forms and, in most situations, would be suitable for supplying at least part of the N to the crop. If recommended levels of N are applied, then the ammoniacal form should have no effect on the availability of other nutrients, such as K and calcium, to the plant.

Some growers become concerned about relative salt indices of fertilizer materials. This concern is generally not that important if soil-test-predicted and crop nutrient requirement amounts of N and K are applied to the crop. In situations where soluble salt injury has been a problem and where well water with high soluble salt content is used, it is even more important to refrain from overfertilization.

Commercial liquid fertilizer materials for injection into drip irrigation systems are often mixtures of N and K. These typically range from solutions that have an analysis of 6-0-6 up to an analysis of 10-0-10. These mixed solutions should be formulated with several factors in mind, including crop nutrient requirement, the soil-test-predicted amount of fertilizers to be applied, and the pumping capacity of the injection system.

Concentrated materials are easier to inject because shorter injection cycles are required to inject the same amount of nutrient as compared to a more dilute fertilizer solution. In cropping situations where the soils test very low in K (so that the total crop nutrient requirement of K is supplied from fertilizer), fertilizer materials such as 7-0-7, 8-0-8, or 10-0-10 are satisfactory for most vegetable crops. Growers should purchase as high an analysis of liquid fertilizer as possible to avoid purchasing large amounts of water. In some situations, particularly those where the soil already contains large amounts of K, it might be possible to inject single-nutrient solutions such as 19% or 28% N solution. These N solutions are usually mixtures of ammonium nitrate and urea in various proportions.

Weather conditions have a great effect on the solubility of fertilizer solutions. Higher concentrations of N and K can be maintained in solution under warm weather conditions compared to cooler temperatures. For example, fertilizer solutions used in the early fall or late spring might be as high as 10 or 12% N and K. However, in the winter under cooler temperatures, lower concentrations will be required to avoid precipitation or "salting-out" of fertilizer elements. This "salting-out" potential must be taken into consideration when fertilizer solutions are purchased. Growers may want to purchase smaller amounts more frequently for injection during winter conditions so that the solution does not sit in a field tank too long.

Some growers may want to investigate the possibility of formulating their own liquid nutrient solutions. This approach might be especially feasible for growers with extensive acreage of drip-irrigated vegetables or for small growers who use only very