Preventing orchard establishment and management pitfalls with online tools
Originally in West Coast Nut
Mae Culumber University of California Cooperative Extension Nut Crop Advisor, Fresno County
Nut crop commodity growth has been explosive in California’s San Joaquin Valley in recent years, requiring new and expanding operations to develop on increasingly marginal soils. Much of the available acreage has been in long-term grape or cotton production, crops that are generally tolerant of these soil conditions. Perennial tree crops by contrast can have the greatest yield and quality potential when established on deep uniform productive soils. The probable tradeoffs of orchard establishment in areas characterized by poor uniformity, fertility, drainage, high salinity, and structural problems requires careful consideration. A thorough evaluation before planting can help identify the appropriate pre-plant modifications and help guide long term management actions that may improve substandard growing conditions and increase long-term profitable production and return on investment. Proper site evaluation can be a daunting task, especially for growers for which tree crops are a new venture. There are several online tools and phone applications that can facilitate the process of site evaluation and planning for a new orchard.
Soil evaluation
A proper site assessment should focus on the physical and chemical soil characteristics likely to present challenges in tree growth and yield potential. Identifying latent soil issues is an important first step in determining what modifications are necessary to maximize tree root development and water drainage. Online soil survey tools can be used to understand the general characteristics of a location. The University of California Davis Soil Resources Lab casoilresouce.lawr.ucdavis.edu has developed several free products designed to allow easy access and interpretation of USDA-NCSS soil survey data. Soil Web tools are accessible on desktop PCs, tablets, and smartphones. The website provides searchable maps with soil classification layers, which can be used to identify soil type variability across the field with depth (Figure 1).
Commonly occurring soil series in the San Joaquin Valley vary from “clay-rich” to "beach sand’ in texture. Although it is easy to assume what type of soil you have based on what you can see on the surface, many areas are characterized stratified, restrictive, claypan and hardpan soil layers in the subsoil. Understanding these physical impediments is important for the selection of the most effective and economical soil modification approaches. Understanding the soil type you are working with is also very beneficial for choosing the most suitable rootstocks, orchard layout design, irrigation system and scheduling. Soil sampling at 1’ depth intervals to 5’ is an important first step to understanding the uniformity of soil type and chemistry before establishing a new orchard. If not already familiar with the orchard site, it may be difficult to know which areas are most representative of field variability. This information can be used to identify the best locations for backhoe pits and additional composite soil samples for chemical analyses. More information about the most important aspects of proper sampling equipment, choosing the proper locations and timing as well as demonstrations of proper sampling techniques are available to view in a four part series offered by the UC Fruit and Nut Research and Information Center. http://fruitsandnuts.ucdavis.edu/photogallery/Soil_Sampling_Video_series/
Figure 1. The SoilWeb Earth tool allows you to view maps in a 3-D display. You must have Google Earth or some other means of viewing KML files installed on your desktop computer, tablet, or smartphone.
Salinity management
Soil chemical analyses can provide a broad indication of soil fertility, identify soil reclamation requirements, and can be used to calculate which amendments are most suitable to reduce toxic salt levels and improve drainage before establishing a new orchard. Pre-planting soil analyses can help guide decisions about which crop, rootstock and variety is most suitable for a site. Soil pH, cation exchange capacity (CEC), saturation percentage, electrical conductivity (EC), and sodium absorption ratio (SAR) are the main factors used to calculate amendment rates and leaching fractions. The Kern County UCCE website cekern.ucanr.edu/Irrigation_Management/ provides downloadable fillable excel spreadsheets to assist orchard managers in making amendment rate and leaching fraction determinations based on soil and water analytical reports (Figure 2).
Figure 2. UCCE Kern fillable spreadsheets are designed for farm managers to input information from soil chemical analyses to make leaching fraction and amendment determinations.
Fertility Management
With the recent implementation of the Nutrient Management Plan, an increasing number of online guidelines are available to facilitate the efficient use of fertilizers for young and established orchard trees. Nutrient applications often exceed what is required by a young developing tree. Applications more than 4 ounces per tree (the equivalent of 20-45 lbs/N acre) in the first year have not shown a benefit in terms of increased growth (Doll, 2012). A collaboration between the California Department Food and Agriculture (CDFA), the Fertilizer Research and Education Program (FREP), and the UC Davis Department of Plant Sciences have developed a mobile friendly app that outlines orchard nitrogen (N), phosphorus (P), and potassium (K) needs, timing, application rates, and fertilizer types and for young and bearing aged trees. https://apps1.cdfa.ca.gov/fertilizerresearch/docs/Almonds.html (Figure 3).
The Almond Nitrogen Calculator https://www.sustinablealmondgrowing.org/ is another online and mobile app resource developed by Sureharvest, the Almond Board of California, and UC Davis Department of Plant and Sciences, which generates a Nitrogen Management Plan as required by the Irrigated Lands Regulatory Program (ILRP). Users can input N contributions from non-fertilizer sources including groundwater, compost, and cover crops. The site provides fertilizer calculators to help managers more accurately determine application rates. The in-season nutrient management plan can be modified when nutrient values from April collected leaf samples and crop load estimates are inputted.
Figure 3 Fertilization guidelines on this CDFA-FREP sponsored website are based on results from orchard studies conducted by University of California researchers and Cooperative Extension advisors.
Irrigation scheduling
Knowing when and how much water young trees need can seemingly require a lot of guess work. Intuitively most of us look to the soil moisture to determine when to irrigate. However, the appropriate frequency of irrigation is not just a function of the moisture content of the soil, but also the water requirements of the tree. Direct relationships have been observed between plant water stress levels, growth, and productivity. As trees deplete water resources in the root zone, water movement becomes more difficult as tension increases within plant cell walls. The level of tension can be observed with an instrument commonly known as a “pressure bomb”. Plant water stress is a function of available soil moisture, temperature and humidity. These relationships have been used to establish guidelines for irrigation scheduling in numerous crops. An interactive website is available to compare field observed plant water status readings to baseline measurements for a well-watered tree. Users can select the closest CIMIS weather station and the time readings were taken to generate baseline tables for several different tree crops (Figure 4). Generally, if observed readings are more than two bars below the threshold for a well-watered tree, it is time to irrigate.
Orchard management can be a daunting task. Researchers recognize that many orchard managers would benefit from readily accessible, fast, easy to use online tools. This article has outlined a few resources currently available to growers, with the anticipation that the development of many more web based tools are on the near horizon.
