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ARS Home » Pacific West Area » Logan, Utah » Forage and Range Research » Research » Publications at this Location » Publication #377538

Research Project: Improved Plant Genetic Resources and Methodologies for Rangelands, Pastures, and Turf Landscapes in the Semiarid Western U.S.

Location: Forage and Range Research

Title: Forage quantity and quality dynamics due to weathering over the dry season on California annual rangelands

item LARSEN, ROYCE - University Of California
item SHAPERO, MATTHEW - University Of California
item STRIBY, KARL - US Department Of Agriculture (USDA)
item ALTHOUSE, LYNNEDEE - Althouse And Meade, Inc
item MEADE, DANIEL - Althouse And Meade, Inc
item BROWN, KATIE - Althouse And Meade, Inc
item HORNEY, MARC - California Polytechnic State University
item RAO, DEVII - University Of California
item DAVY, JOSH - University Of California
item Rigby, Craig
item Jensen, Kevin
item DAHLGREN, RANDY - University Of California

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2021
Publication Date: 3/10/2021
Citation: Larsen, R.E., Shapero, M., Striby, K., Althouse, L., Meade, D.E., Brown, K., Horney, M.R., Rao, D.R., Davy, J.S., Rigby, C.W., Jensen, K.B., Dahlgren, R.A. 2021. Forage quantity and quality dynamics due to weathering over the dry season on California annual rangelands. Rangeland Ecology and Management. 76:150-156.

Interpretive Summary: There are an estimated 23 million ha of grazed rangelands in California. These rangelands support ~660,000 head of beef cattle and over 650,000 sheep and goats making these rangelands an important economic resource. California’s Mediterranean climate, with cool-moist winters and hot-dry summers. This paper describes biomass and forage nutritional losses of above-ground biomass production through the dry season, May through October, on the Central Coast of California. This study describes biomass and nutritional losses across a large rainfall gradient and spanning three contrasting rainfall years. Overall, our results showed an average above-ground biomass loss of ~50% over the summer that can be used as a general guideline; however, considerations are also required to account for greater losses in years with lower peak biomass production. Changes in forage nutritional quality observed in this study over the summer weathering period have direct implications to management.

Technical Abstract: We examined the loss of above-ground standing biomass throughout the dormant summer period on California annual rangelands. Twenty-five sites spanning a rainfall gradient (183 – 492 mm) were examined over three contrasting rainfall years (20152017; 58 - 157% of average precipitation). Overall fractional biomass loss was ~50% (range = 42.9 – 60.5%) with greater fractional losses occurring in dry years. Biomass losses were related to the amount of peak standing crop and plant composition which were both a function of annual precipitation. The peak standing crop and fractional seasonal losses were 2015 = 1323 kg/ha with 60.5% (9.6% monthly), 2016 = 1742 kg/ha with 51.8% (8.2% monthly) and 2017 = 2296 kg/ha with 42.9% (6.8% monthly). Forage quality metrics were strongly affected by summer weathering processes. Crude protein concentrations decreased by 19.7 to 33.6% with the largest reductions occurring in dry years. In contrast, concentrations of acid detergent fiber (ADF = cellulose + lignin) and lignin in the weathered biomass showed increases of 23.9 to 44.2% and 5.6 to 27.8%, respectively, with greater increases in wetter years. While ADF and lignin concentrations increased during the weathering process, the standing stock (weathered biomass, kg/ha) of these constituents decreased by 39.9% (ADF) and 45.5% (lignin), compared to an overall weathered biomass loss of 51.8%. We attribute the overall loss of biomass, crude protein, ADF and lignin standing stocks in weathered biomass primarily to degradation (physical and photodegradation) following senescence, and to seed shattering and fragmentation of the weathered biomass. Overall, we found a significant loss of above-ground biomass and forage quality as weathering processes occurred throughout the dry summer period, which affects livestock grazing strategies and residual dry matter (RDM) guidelines for erosion control and nutrient cycling prior to the onset of the winter rainy season.