In the last blog we showed some pictures showing the difference in poor soil quality and good soil quality and its effect on water infiltration.

After 1 day of sun the ponding decreased, however an additional 0.5” resulted in ponding again, the garden did not pond.

Poor infiltration leads to in-season water stress. Water stress limits the development of young plants and reduces grain fill and development fruiting plants. Water stress also raises leaf temperature, which increases the likelihood of severe spider mite infestations.

Slow water intake reduces irrigation efficiency since a greater portion of the water applied is lost to evaporation. Finally, slow water intake increases the potential for compaction since planting and harvesting are often performed before the soil is sufficiently dry.

Slow water intake can result in prolonged standing water, which reduces the needed oxygen required for proper soil health. Standing water can cause N loss by waterlogging soil bacteria. The bacteria starving for oxygen, will scavenge oxygen from soil nitrate. As a side effect, these scavenging bacteria break down the nitrate molecules, causing de-nitrification.

The Common causes of poor infiltration are:
1. Compaction of surface soil from traffic.
2. High sodium content (Na) causes soil particles to be forced apart chemically (called deflocculation). This can result in surface sealing by reducing pore size.
3. Inadequate salt content of the surface soil is just as big a factor in slow infiltration as high content. Irrigating with low salt water (less than 250ppm) or excessive rainfall, which is very low in salt content eventually, leaches enough salts from the surface soil to reduce its structure. This creates smaller pore spaces, which have higher surface tension, and less permeability.
4. Subsurface soils with distinctly different texture are often overlooked as a water related problem. It does not cause slow infiltration at the soil surface; rather it limits downward movement of water into the lower root zone. Soils of different texture vary greatly in the number and size of air spaces through which water travels. When downward moving water encounters a zone of different soil texture, it must overcome the surface tension created by the different pore size. Saturated soil conditions occur above the layer until sufficient pressure (head) builds up to overcome this.

Suggestions for improving the infiltration rate:
1. After harvest, dig in several locations to test for compacted soils 8-10 inches below the surface. If you can stand on the shovel without it penetrating, consider chiseling the soil after harvest when the soil is dry. Chiseling can correct surface soil compaction from traffic and can markedly improve water infiltration. However depending upon the soil type, some growers find discover chiseling lasts for only two or three irrigations. Soil analysis, amendments and winter cover cropping are need for longer-term management.
2. Soil sample. Include only the first inch from several locations. Sample areas with good and bad intake rates separately. Request a basic salinity analysis including a SAR (sodium adsorption ratio) or ESP (exchangeable sodium percentage). Also ask that the gypsum requirement be calculated. Soils with total salt content (EC) less than about 1.0 mmho/cm often benefit from gypsum application. This raises the beneficial salt content of the surface soil and improves structure. Soils with SAR or ESP values greater than about 7 can also benefit from SuperCal SO4 application by displacing sodium salts with calcium from the gypsum. If you do not understand the results of your soil analysis, let us know we can help you understand it.
3. Sample your main water source. Irrigation water can be either low or high in salts, depending on your location. Continual use of low salt water causes soil to loose structure. Use of high salt water causes the soil surface to seal shut. SuperCal SO4 application on the soil in the spring will restore or remove the salts and improve water intake.
4. Soils not showing compaction of salt problems require investigation at greater depths with a backhoe. Have an individual knowledgeable about soils and roots present to assist you in their evaluation. Soil layering creates resistance to water movement and root development. Such conditions are difficult to impossible to correct. Deep ripping with the intent of modifying subsoils lacking a hardpan will not solve a soil stratification problem. The benefit of deep ripping is usually gone by the next season as the soil reassumes its original structure. Adjustments in irrigation management or investment in a low volume system allowing more precise water application is usually of greatest benefit.
5. Cover cropping often improves poor surface structure. Cover crops can produce many tons of dry matter per planted acre if allowed to grow until almost mature. As it decomposes, it creates humus, which is important to improving soil structure. Great numbers of pores are also created from the decayed roots. This is not a quick fix! Research and grower testing, show three years of regular cover cropping is needed before improvements were noticeable.

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