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The first waterworks for irrigation and other uses in California were built by Franciscan padres at Mission San Diego (1773) and Pueblo de Los Angeles (1781). The first large-scale irrigation developed in the mid 1800’s by gravity diversion of the Santa Ana River by the Mormon colony at San Bernardino (1851) and the San Joaquin River by Miller and Lux in western San Joaquin Valley (1850-1860). Since then, rapid expansion in irrigated agriculture occurred through the mid 1900’s through the establishment of major water projects by local water districts, and state and federal agencies. Subsequently, the late 1900’s presented itself with significant changes in agricultural water management, because of environmental and ecological constraints, competition for water quantity and water quality with other sectors of society, and growing water conservation measures. Most recently, this has led to the CALFED Bay-Delta Program and increasing public awareness of water quantity and water quality issues in the State.

The quality of soils, ground and surface waters is specifically vulnerable in climatic regions where agricultural production is possible only by irrigation such as in California (USA) and in many other (semi-) arid regions of the world. The regular excessive application of nitrogen fertilizers with irrigation water is likely responsible for the increase in nitrate concentrations of groundwater resources in these areas. Specifically, nonpoint source pollution of nitrate in groundwater is a major problem in many areas of California such as the Salinas Valley, Santa Maria Valley, and along the eastside of the San Joaquin Valley. As a result, nitrate concentrations in groundwater exceeds the drinking water standard in these areas. Therefore, alternative irrigation water and soil management practices are needed that tactically allocate water and fertilizers to maximize their application efficiency, by minimizing fertilizer losses through leaching towards the groundwater.

In addition, salinization affects about 20-30 million ha of the world’s current 260 million ha of irrigated land , and limits world food production. Salinity reduces water availability to plants by the accumulation of dissolved mineral salts in waters and soils due to evaporation, transpiration, and mineral dissolution. Subsequent salt leaching leads to salt buildup in shallow groundwater (near plant root-zone) and deeper groundwater bodies (aquifers).

A. Multi-dimensional simulation of irrigation and fertigation

B . Field and Regional Scale Salinity Processes

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A. Multi-dimensional simulation of irrigation and fertigation

The regular application of nitrogen fertilizers by irrigation is likely responsible for the increase in nitrate concentrations of groundwater in areas dominated by irrigated agriculture. Consequently, sustainable agricultural systems must include environmentally-sound irrigation practices. To reduce the harmful effects of irrigated agriculture on the environment, the evaluation of alternative irrigation water management practices is essential. Micro-irrigation offers a large degree of control, enabling accurate application according to crop water requirements, thereby minimize leaching. Furthermore, fertigation allows the controlled placement of nutrients near the plant roots, reducing fertilizer losses through leaching into the groundwater. The presented two-dimensional modeling approach using HYDRUS-2D provides information to improve fertigation practices. The specific objective of this project was to assess the effect of fertigation strategy and soil type on nitrate leaching potential for four different micro-irrigation systems.

Publications:

Gardenas, A., J.W. Hopmans, B.R. Hanson, and J. Šimunek. 2005. Two-dimensional modeling of Nitrate Leaching for Different Fertigation Strategies under Micro-Irrigation. Agric. Water Management 74:219-242. DOWNLOAD: PDF

Koumanov, K. S., J.W. Hopmans, L.J. Schwankl, L. Andreu, and A. Tuli. 1997. Application efficiency of micro-sprinkler irrigation of almond trees. Agricultural Water Management 34:247-263. DOWNLOAD: PDF

Andreu, L., J.W. Hopmans and L.J. Schwankl. 1997. Spatial and temporal distribution of soil water balance for a drip-irrigated almond tree. Agricultural Water Management 35:123- 146. DOWNLOAD: PDF

Koumanov, K., J.W. Hopmans and L.J. Schwankl. 2005. Soil water dynamics in the root zone of a micro-sprinkler irrigated almond tree. IN: Proceedings of the IVth International Symposum on Irrigation of Horticultural Crops (Ed. R. L. Snyder), Sept 1-6, 2003. Davis, CA. Acta Horticulturae, ISHS 664: 369-373.

Schwankl, L.J, J.Pl Edstrom, J.W. Hopmans, L. Andreu and K.S. Koumanov. 1999. Micro sprinklers wet larger soil volume; boost almond yield, tree growth. California Agriculture Vol. 53(2):39-43.

Vogel, T. and J. W. Hopmans. 1992. Two-dimensional analysis of furrow irrigation. J. of Irrigation and Drainage Eng. Amer. Soc. Civil. Eng. 118(5):791-806.

B. Field and Regional Scale Salinity Processes

Salinity.avi - This short movie shows the changes in soil
salinity in the western SJV since 1940. Download: Movie

Salinization affects about 20-30 million ha of the world’s current 260 million ha of irrigated land , and limits world food production. Salinity reduces water availability to plants by the accumulation of dissolved mineral salts in waters and soils due to evaporation, transpiration, and mineral dissolution. Subsequent salt leaching leads to salt buildup in shallow groundwater (near plant root-zone) and deeper groundwater bodies (aquifers). The San Joaquin Valley, which makes up the southern portion of California’s Central Valley, is among the most productive farming areas in the United States, however, salt buildup in the soils and groundwater are threatening its productivity and sustainability.

Currently, there is a good understanding of the fundamental soil hydrological and chemical processes that control soil and groundwater salinity. This was achieved by considering the hydrology and soil chemistry separately, assuming simplified steady state flow for spatial scales not larger than the field and only considering the root-zone. However, recent research has shown that soils must be fully coupled with the vadose zone and groundwater systems for regional-scale studies, especially in areas where groundwater tables are shallow or groundwater pumping is used. Innovative predictive tools are needed that can be applied at the basin scale and at the long term, so that the sustainability of alternative management strategies can be evaluated. We developed an integrated regional-scale hydro-salinity model that fully couples the hydrology and salt chemistry of the vadose zone with the groundwater so that historical changes in soil and groundwater salinization can be reconstructed in general and for the western San Joaquin Valley, CA, specifically.

Publications:
Schoups, G. J.W. Hopmans, and K.K. Tanji. 2004. Evaluation of model complexity and space-time resolution on the prediction of long-term soil salinity dynamics. In press. Hydrologic Processes. DOWNLOAD: PDF

Schoups, G.H. J.W. Hopmans, C.A. Young, J. Vrugt, W.W. Wallender, K.T. Tanji, and S. Pandy. Sustainability of irrigated agriculture in the San Joaquin Valley, California. Submitted

Related salinity research:

Corwin D.L., S. R. Kaffka, J.W. Hopmans, Y. Mori, J. W. van Groenigen, C. van Kessel, S. M. Lesch, and J.D. Oster. 2003. Assessment and Field-scale Mapping of Soil Quality Properties of a Saline-sodic Soil. Geoderma 1952:1-29. DOWNLOAD: PDF

Eching, S.O., J.W. Hopmans, W.W. Wallender, J.L. MacIntyre, and D. Peters. 1994. Estimation of local and regional components of drain flow from an irrigated field. Irrig. Sci. 15:153-157.

Childs, J. L., W. W. Wallender, and J. W. Hopmans. 1993. Spatial and seasonal variation of furrow infiltration. J. of Irrigation and Drainage Eng. Amer. Soc. Civil. Eng. 119(1):74-90.

Shepard, S.G., W.W. Wallender, and J.W. Hopmans. 1993. One-point method for estimating furrow infiltration. Trans. Amer. Soc. Agric. Eng. Vol 36(2):395-404.