Introduction

In numerous publications world-wide, planting hole recommendations for avocado and other subtropical crops are made for large holes from 2 feet by 2 by 2 to as much as a cubic yard.  These recommendations also include incorporation of manures or composts comprising 25% by volume with the native soil.  I have noted the use of large holes and amendments in several countries, including New Zealand, Guatemala, Brazil, Costa Rica, Mexico and the United States.

The various reasons given for making these large holes are to disrupt any compaction or limiting soil layers and to create a more conducive environment for root growth.  In the case of replanting deciduous orchards, McKenry found it to be beneficial in actually replacing the native soil in the hole with pathogen free soil. In many cases, research has shown that holes much larger than the planting ball and using organic amendments can cause problems for many tree species.  Improper mixing of the organic amendment can cause anaerobic conditions and settling due to amendment decomposition.  Soil that has not been properly firmed in the hole can also lead to plant settling and stems can drop below grade leading to crown rot.

Nonetheless, on the basis of recommendations made in many countries there could be some value in these planting practices, especially in the light of the effect organic matter has on avocado root rot. Numerous studies have shown organic matter suppresses the causal agent of root rot.  This study evaluated the effect of hole size and amendments on avocado growth in an ideal environment with excellent soil conditions and in a more harsh one with heavy soil texture and the presence of the root rot pathogen.

Materials and methods

On the north island of New Zealand in the Bay of Plenty, 20 trees each were planted to one of four treatments: a) small holes (12 by 18 inches) without amendment; b) small holes with 25% by volume compost; c) big holes (60 deep by 30 wide by 24 wide inches) without amendment and d) big holes with 25% by volume compost.  Big holes were dug with a backhoe, while small holes were dug by shovel.  Trees were approximately 2 feet tall at planting.  Soil was a deep sandy loam at both sites.  Trees were irrigated by drip irrigation.  Trees were ‘Hass’ on ‘Zutano’ seedling rootstock.  Trees were planted the second week of spring 2000.  Tree height, trunk caliper and canopy volume were measured on a monthly basis for eight months and then twice a year for the next year.  In Carpinteria, California a similar trial was established using ‘Hass’ on ‘Toro Canyon’ rootstock.  Trees were approximately 2 feet tall at planting.  The grove had a heavy clay loam soil and a history of root rot.  The trees were on drip irrigation.  The trees were planted summer 2001 and monitored for 18 months after planting.

Results and discussion

Figures 1and 2 show the results of the different planting treatments at sites in New Zealand on ideal soils and on the heavy soil infected with root rot in California.  Only tree height is shown; trunk girth and canopy volume followed similar patterns.  From planting onwards, there were no differences in tree growth in any of the treatments at any of the sites.  This would lead one to the conclusion that there is no value in and a great expense in making big holes and incorporating amendment.  This is especially so in hillside situations where moving equipment and amendments on steep slopes would be very difficult.

The trees at the Carpinteria site, although infested with root rot, all looked good.  The addition of organic matter in conjunction with the clonal rootstocks did not apparently provide any greater disease resistance.  This is in accordance with work done by John Menge which shows that the greatest benefit derived from mulching are seedling rootstocks.  The effect of mulch on disease suppression diminishes with the rootstock’s resistance to root rot.

Figure 1.  Tree height (meters) at site 1 in New Zealand 20 months after planting.  No differences were found at the 5% level of significance.

Figure 1

Figure 2.  Tree height (meters) in California 18 months after planting.  No differences were found at the 5% level of significance.

Figure 2

Avocados planted on steep slopes.

University of California (UC) researchers and private industry consultants have invested much effort in correlating optimal citrus tree growth, fruit quality and yield to concentrations of necessary plant nutrients in citrus (especially orange) leaf tissue. The grower can remove much of the guesswork of fertilization by adhering to UC recommendations of critical levels of nutrients in the tissues of appropriately sampled leaves.  Optimal values for elements important in plant nutrition are presented on a dry-weight basis in Table 1.  Adding them in appropriate rates by broadcasting to the soil, fertigating through the irrigation system or spraying them foliarly may correct concentrations of nutrients in the deficient or low range.  Compared to the cost of fertilizers, and the loss of fruit yield and quality that can occur as a result of nutrient deficiencies or excesses, leaf tissue analysis is a bargain.   At a minimum, the grower should monitor the nitrogen status of the grove through tissue sampling on an annual basis.

Leaves of the spring flush are sampled during the time period from about August 15 through October 15.  Pick healthy, undamaged leaves that are 4-6 months old on non-fruiting branches.  Select leaves that reflect the average size leaf for the spring flush and do not pick the terminal leaf of a branch.  Typically 75 to 100 leaves from a uniform 20- acre block of citrus are sufficient for testing. Generally, the sampler will walk diagonally across the area to be sampled, and randomly pick leaves, one per tree.  Leaves should be taken so that the final sample includes roughly the same number of leaves from each of the four quadrants of the tree canopy.  Values in Table 1 will not reflect the nutritional status of the orchard if these sampling guidelines are not followed. Typically, citrus is able to store considerable quantities of nutrients in the tree.  Sampling leaves from trees more frequently than once a year in the fall is usually unnecessary.  A single annual sample in the fall provides ample time for detecting and correcting developing deficiencies.

Table 1.  Mineral nutrition standards for leaves from mature orange trees based on dry-weight concentration of elements in 4 to 7 month old spring flush leaves from non-fruiting branch terminals.

*California and Florida recommendations for K are sufficiently different that they are presented separately.  The California standards are based on production of table navels and Valencias, and those for Florida were developed primarily for juice oranges like Valencia.

The sampled leaves should be placed in a paper bag, and protected from excessive heat (like in a hot trunk or cab) during the day.  If possible, find a laboratory that will wash the leaves as part of their procedure instead of requiring the sampler to do this.  Leaf samples can be held in the refrigerator (not the freezer) overnight.  Leaves should be taken to the lab for washing and analysis as quickly as is feasible.

Often separate samples are taken  within a block if areas exist that appear to have special nutrient problems.  The temptation encountered in sampling areas with weak trees is to take the worst looking, most severely chlorotic or necrotic leaves on the tree.  Selecting this type of leaf may be counter-productive in that the tree may have already reabsorbed most of the nutrients from these leaves before they were sampled. A leaf-tissue analysis based on leaves like this often results in a report of general starvation, and the true cause of the tree decline if the result of a single nutritional deficiency may not be obvious.  Often in weak areas, it is beneficial to sample normal appearing or slightly affected leaves.  If the problem is a deficiency, the nutrient will, generally, be deficient in the healthy-looking tissue as well.

Groves of early navels that are not normally treated with copper and lime as a fungicide should include an analysis for copper. Copper deficiency is a real possibility on trees growing in sandy, organic, or calcareous soils.  For later harvested varieties, leaves should be sampled before fall fungicidal or nutritional sprays are applied because nutrients adhering to the exterior of leaves will give an inaccurate picture of the actual nutritional status of the tree.

Usually leaf samples taken from trees deficient in nitrogen will overestimate the true quantity of nitrogen storage in the trees. Trees deficient in nitrogen typically rob nitrogen from older leaves to use in the production of new leaves.  Frequently, by the time fall leaf samples are collected in nitrogen deficient groves, these spent spring flush leaves have already fallen.  Nitrogen deficient trees typically have thin-looking canopies as a result of this physiological response.  Since the spring flush leaves are no longer present on the tree in the fall when leaves are sampled, younger leaves are often taken by mistake for analysis. These leaves are higher in nitrogen than the now missing spring flush leaves would have been and provide an inaccurately higher nitrogen status in the grove than actually exists.

Critical levels for leaf-nitrogen for some varieties of citrus, like the grapefruits, pummelos, pummelo x grapefruit hybrids and the mandarins, have not been investigated as well as those for oranges.  However, the mineral nutrient requirements of most citrus varieties are probably similar to those for sweet oranges presented in Table 1, except for lemons, where the recommended nitrogen dry-weight percentage is in the range of 2.2- 2.4%.

A complete soil sample in conjunction with the leaf sample can provide valuable information on the native fertility of the soil with respect to some mineral nutrients and information on how best to amend the soil if necessary to improve uptake of fertilizers and improve water infiltration.

Iron deficiency of citrus

(Table 1. Broadleaf (pigweed and black nightshade) weed control (% control at 15 days a   er treatment), when treated  12, 19, or 26 days after emergence.

Table 2. Grass (Barnyardgrass and crabgrass) weed control (% control at 15 days after treatment), when treated 12, 19, or 26 days after emergence.

*  Values for comparing any two means.  Pigweed and mustard were each analyzed separately.

Organic weed control.

Go directly to resources.

Some growers are reconsidering avocado production.

A question from San Luis Obispo County – “Should I pull out my wine grapes and plant avocados?”  Maybe these growers can consider a swap! It’s more likely that they need to research the resources needed to grow each of these crops and the market history and potential for the product.

Locating information on resource needs and markets for new crop enterprises can be challenging.  In an article,  ‘Considerations In Enterprise Selection’, Karen Klonsky, Extension Specialist Department of Ag Economics UC Davis, and Patricia Allen, Agroecology Program UC Santa Cruz provide insight into the process of evaluating existing crops and selecting new crops.  Much of the following discussion is excerpted from their 2001 article.

Klonsky and Allen discuss the importance of setting goals for the enterprise – know where you’re going.  A careful inventory of available physical, financial and management resources lets you know what you already have to help yourself get there.  An understanding of the resource needs of potential new enterprises will outline the physical, financial and management resources you need to acquire to make the new enterprise successful.  Finally, a thorough knowledge of the market you will need to access is critical.

INVENTORY YOUR RESOURCES

The availability of resources will ultimately direct your choice of enterprises simply because the resource requirements among enterprises vary.  Resources typically include land, labor and capital, but also include climate, management skills, and access to information and markets.

Carefully evaluate the potential for each of the crops you are considering. Systematically compare the resource needs for each crop to the resources available. Talk to other growers in your area or elsewhere about their experience with the crop you are considering.

Cost estimates of resources needed for establishment and production are often not easily obtained, particularly for crops new to an area.  Cost and return studies for some crops in California are available for download from the UC Department of Agriculture and Resource Economics at   http://coststudies.ucdavis.edu/.

These cost and return studies offer a way of comparing your current enterprise costs with a potential new enterprise.  They can give you a picture of the cultural operations, labor, and equipment needs and costs for a new enterprise.    There may not be a cost and return study for your location for the crop of interest.  Reviewing the information for several areas can help provide some general information.  For instance, there are current cost and return studies for wine grapes for Lake, Sonoma, and Napa Counties, and the Sacramento/San Joaquin areas.  Certainly costs might differ for wine grapes in Southern California, but many of the cultural practices, labor, and equipment needs will be similar. Review each item carefully since costs may vary widely.  In 2007, studies for blueberry production in Ventura/Santa Barbara and San Obispo County and guavas in San Diego County showed a $385/acre-foot difference in irrigation water cost between the two areas.

MARKET ACCESS AND INFORMATION

Access to markets is the most commonly overlooked factor in the enterprise selection process. But in fact it can be your most limiting constraint. Simply because you can grow something does not mean you can sell it. And just because you can sell a product does not mean that it will be profitable. A third possibility is that you will be able to sell a product at a money making price but that you will only be able to sell a limited amount of the product; that is, less than the total amount that you are able to produce.

Developed in partnership with the UC Small Farm Program and co-authored by UC Farm Advisor Ramiro Lobo in 2008, the  Market-Driven Enterprise Screening Guide provides an organized tool for goal setting and inventory.  This guide provides a series of questions to help farmers self-evaluate their knowledge of potential new crops or products and the potential for to their farming business.

This guide will help you to answer questions like the following about marketing your new crop:

• Do you have a preferred marketing method?  Broker, retailer, direct (roadside stand, farmers market, U-pick), cooperative, contract with processor?
• How much time are you willing to spend marketing your products?
• What is your proximity to various potential markets?
• Have you contacted potential markets for their advice on crop or variety selection?
• Are you familiar with market quality standards for the crops you are considering?
• Have you studied the market history and market trends of the crop?

Following are additional information sources to help answer these questions:

California Department of Food and Agriculture’s Agricultural Resource Directory can be downloaded for free. It provides commodity information summaries by county as well as extensive lists of many of the agencies and organizations included in this article.

Marketing orders and commissions are set up to aid in marketing some commodities and establishing standards for size, grade, and/or maturity.  There are federal and state marketing orders and commissions.  Some assess fees to growers to pay for research, advertising, or promotion.  Links to marketing orders and commissions for specific crops can be accessed by clicking here.

The USDA Agricultural Marketing Service (AMS) administers programs that facilitate marketing of U.S. agricultural products, including food, fiber, and specialty crops. AMS issued its first Market News report in 1915. Today, Fruit and Vegetable Market News disseminates detailed information on marketing conditions for hundreds of agricultural commodities at major domestic and international wholesale markets, production areas, and ports of entry. Using direct contacts with sales persons, suppliers, brokers, and buyers, Market News reporters collect, validate, analyze, and organize unbiased data on price, volume, quality and condition, making it available within hours of collection at no cost to you.  You can subscribe to Fruit and Vegetable Market News here.

Agricultural Marketing Service (AMS) provides a searchable database of Farmer’s Markets listings.  As of mid-2011, there were 7,175 farmers markets operating throughout the U.S. This is a 17 percent increase from 2010. AMS also provides information about the  National Organics Program.

Organic agricultural operations have special needs for production, planning, and management beyond those of conventional farms because of limitations imposed by the terms of organic registration and certification. At present, registration is a legal requirement and certification is a private process independent of government and used by growers and marketers to maintain the integrity of the organic product. Additional information about the certification process to produce organic foods, along with contacts for certifying groups, is available at http://anrcatalog.ucdavis.edu/pdf/7247.pdf

California Ag Statistics Service publishes reports of crops weather as well as field crop and fruit and nut reports weekly.  Data is submitted voluntarily by growers and agribusiness.

Researching new enterprise resource requirements and markets takes time.  Klonsky and Allen note in their article that playing ‘what if’ on paper is always less risky and less time consuming than experimenting in the field when you are not well prepared.

Additional Resources:

Information for specific commodities can also be found online.  Our San Diego and San Luis Obispo growers looking to change their enterprises might find useful information at the following sites.

Avocado Information http://ucavo.ucr.edu/ is a University of California link that contains information on varieties, irrigation, market standards, and links to additional avocado-related sites.

California Avocado Commission contains information on crop projection, yield and price, research  and weather.

California Association of Winegrape Growers was founded to represent the interests and concerns of wine and concentrate grape growers.

WineFiles is a project of the Sonoma County Wine Library.  It includes citations, abstracts and links to articles in the technical, academic, trade and consumer wine periodicals as well as newspaper articles, government documents, press releases, advertising brochures and other ephemera dealing with wine.

Grape Crush Report, produced by the California Ag Statistics Service, CDFA, provides details of the crushed tonnage, and weighted average prices reported by grape type and variety, as well as by grape pricing districts. The districts refer to the area in the state in which grapes are grown, for example San Diego = District 16 and San Luis Obispo = District 8.

Grape Acreage Reports, produced by the California Ag Statistics Service, CDFA, provide acreage statistics by grape type: acreage standing (bearing and non-bearing) by year planted, by county.

The data can be quite different from that reported by the county Agricultural Commissioner’s office. Click here for a summary of County Agricultural Commissioners reports.