Water and nitrogen use efficiencies of sub-surface drip irrigated and fertilized forage corn and sorghum in the San Joaquin Valley

Summary:

During the recent drought, interest in forage sorghums increased as it could be a more drought-tolerant alternative to corn. Forage sorghum cultivar responses to a range of water application levels have been tested in recent trials in the San Joaquin Valley, but peak irrigation and fertilizer application rates in these trials were matched to what were thought to be optimal levels for forage sorghums. They did not include treatments where corn was grown at optimal irrigation levels and nitrogen applications. If demonstrated to be practical and economically feasible, these practices may present dairy forage growers with viable options to conserve limited water resources and meet recently enacted regulatory nitrogen management mandates.

Investigator:

Nicholas Clark
Assistant Cooperative Extension Advisor
UC Agriculture and Natural Resources

Project description:

This project continues ongoing research on water and nitrogen use efficiencies of corn and sorghum grown for dairy forage in the southern San Joaquin Valley under sub-surface drip irrigation and fertilization. This irrigation, fertilization, and cropping combination is a mix of innovative and traditional practices. If demonstrated to be practical, economically feasible, and conservative of water and nitrogen from fertilizer, these practices may present dairy forage growers with viable options to conserve limited water resources and meet recently enacted regulatory nitrogen management mandates.

Waste discharge requirements have set an enforceable ratio of applied nitrogen to harvest removed nitrogen. This is presumed to be protective of groundwater quality by minimizing nitrate-nitrogen pollution via leaching. Additionally, the Sustainable Groundwater Management Act requires that by 2040, groundwater levels not be depleted by over-extraction. These two challenges are of critical importance because the region’s groundwater has been identified in several areas as highly vulnerable to both depletion and pollution in connection with intensive irrigated agriculture and dairy operations.

We are completing a small-plot field trial which continued for two years at two sites: the Kearney Agricultural Research and Extension Center and the West Side Research and Extension Center. These two sites were chosen on the basis of comparing two typical soil types with different water holding capacities that are expected to affect different rooting depths of the crops. At each site irrigation treatments were 50, 75, and 100% of corn optimum evapotranspiration, or crop water use, and fertilization treatments were 0, 100, and 250-300 lbs N/acre. Several corn and sorghum varieties were factored into the study. The main effects estimated were yield, forage quality, and various traits important to crop vitality, such as lodging, plant population, and disease or insect pest incidence.

The anticipated outcomes of this research are 1) a more detailed understanding of the relative nitrogen and water use efficiencies between forage corn and sorghum, 2) a demonstration of the practicality of corn and sorghum in two typical soils, and 3) more information on the economic feasibility of fertilized forage corn and sorghum. The impact on water resources in California will likely be beneficial to conservation efforts of ground and surface water reserves as well as to ground water quality with respect to risks of nitrate pollution.