David Doll3 CommentsDecember 15, 2017Irrigation

Is Winter Irrigation Needed?

The reduced late fall rains have led to relatively dry conditions throughout the State. Within the San Joaquin Valley, limited amounts of rain have fallen, with recorded precipitation around one inch in Merced. The lack of rain has led to a series of questions about winter irrigation requirements in which answers are included. Question (Q). Do I need to irrigate now? Answer (A). Evapotranspiration rates are very low and almond water use is even lower. A table has been included that has utilized the real-time evapotranspiration data (ETo), the corresponding crop coefficients (Kc), almond evapotranspiration (ETc) and rainfall for the MERCED CIMIS station. The need to irrigate should be based on almond water use, the amount of water that has been applied in the Late October through early December period, and rainfall. Week Starting: ETo Kc ETc (in) Rain (in) Nov 5th 0.48 0.69 0.3312   Nov 12th 0.38 0.69 0.2622 0.71 Nov 19th 0.34 0.6 0.204   Nov 26th 0.32 0.6 0.192 0.27 Dec 3rd 0.3 0.4 0.12   Total: 1.82   1.1094 0.98 Based on this example, ETc for the month of November and first week of December has been 1.11” with roughly 0.98” of rainfall. This suggests that an irrigation may be needed. If, however, any irrigation was applied in late October or November, most likely the water needs have been met. Water demands and rainfall are site specific. Determining the situation for the orchard location will be needed to determine localized water needs. When in doubt, checking soil moisture status may assist with the decision making. Q. I didn’t irrigate in Late October – December and rainfall has been limited, how do I apply the water? A. Irrigation sets should be shorter than 24 hours to reduce saturated soil conditions and the risk of Phytophthora. If

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David Doll11 CommentsOctober 10, 2015Salinity

Salinity Management for Sandy Soils

AUTHORS NOTE: The following article discusses salinity management considerations for SANDY SOILS (e.g. sands, loamy sands). A follow up post will be made for finer texture soils (loams, silts, and clays). For the most part, this article describes issues with the EAST SIDE of the San Joaquin Valley. NOT ALL SOILS ARE THE SAME. Please note that the following guidelines may need site-specific adjustments. During low rainfall years, salt burn often shows up in sandy soils. This salt burn is a combination of accumulation of sodium within the soil, the use of well water, and the low exchange capacity of the soil. Starting with the soil, we often use the term cation exchange capacity (CEC) which is the amount of cations (positive charged ions like sodium, magnesium, calcium, potassium, etc.) that can bind to the soil particle surface. In the sandier areas on the east side of the San Joaquin Valley, CEC values can be quite low, with values less than 10 meq/100 g of soil. To put that in perspective, sandy loams are in the teens through 20s, silts and clays are in the 30s to 40s. This value is important as it indicates the amount of cations the soil particles can hold. The higher the CEC, the more cations that stick to the soil, preventing them from entering the soil water (soil water is the amount of water that is held between soil particles – it is what the tree drinks), reducing exposure to the roots of the tree. Regardless of the CEC, once the soil is saturated with cations, the excess will stay within the soil water. As the soil salinity increases, the tree’s roots have a greater exposure impacting them by affecting the osmotic movement of water (e.g. essentially making the tree work harder for water) and  eventual toxicity.

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