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Title: INFLUENCE OF SUMMER MANAGEMENT PRACTICES OF GRAZED WHEAT PASTURES ON RUNOFF AND NUTRIENTS

Author
item Daniel, John
item Phillips, William
item Northup, Brian

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2006
Publication Date: 5/1/2006
Citation: Daniel, J.A., Phillips, W.A., Northup, B.K. 2006. Influence of summer management practices of grazed wheat pastures on runoff and nutrients. Transactions of the ASABE. 40(2):349-355.

Interpretive Summary: The agricultural economy of southern Great Plains relies on stocker cattle that graze winter wheat. However, different summer management practices used with grazed winter wheat may influence surface runoff and downstream water quality. While downstream water quality information exists, there is limited data about summer managment practices and the potential impact on downstream water resources. This study examined the surface runoff, and runoff water quality from grazed-ungrazed winter wheat pastures with summer fallow or with grazed-ungrazed summer legumes during 1999 through 2002. Using a rainfall-simulator set to simulate high intensity summer storms, surface runoff and the length of time to acheive runoff was measured. Runoff samples were analyzed for nutrients (nitrate-N, bioavailable and water-soluble phosphorus, and sediment yield. Results indicate summer management practices and grazing can impact surface water resources and potential downstream water quality. The summer fallow practice had greater runoff, higher sediment and nutrient yields then the summer legume. Likewise, grazing produced greater runoff, sediment and nutrients than ungrazed plots. The worst case scenario was grazing winter wheat followed by summer fallow in which 70% of precipitation was lost as runoff, and the largest loss of sediment (284 kg/ha), NO3-N (124 kg/ha), BAP (380 g/ha), and WSP (38 g/ha). Movement of nutrient and sediment can create downstream water quality problems while runoff water is not available for plant establishment and utilization. However, water catchments designed to capture eroded sediment can also capture runoff, restricting the movement of runoff from a watershed. Such catchments can provide immediate relief to livestock and wildlife. Natural depressions and micro depressions can be used to reduce offsite movement of runoff, sediments, and nutrients and provide a mechanism to promote infiltration and allow recharge and storage as ground water.

Technical Abstract: The agricultural system in the southern Great Plains includes practices that incorporate grazed winter wheat. While information exists about the impact of these practices on water quality, data are limited about their potential impact on downstream water resources. This study examined the partitioning of rainfall into infiltration, runoff, and runoff water quality from two pastures replicated (n=2) agricultural management strategies; winter wheat with summer fallow (WWF) and winter-wheat with summer legumes (WWSL), and two grazing treatments (grazed and ungrazed) during 1999 through 2002. Pastures were planted in no-till winter wheat and grazed from November to May. Summer legumes were direct seeded in two pastures in March and grazed mid-July to September. Surface runoff from the plots was measured utilizing a rainfall-simulator which replicated short duration (15 minute), high intensity (10 cm/hour) summer storms. Runoff samples were analyzed for nitrate-N, bioavailable and water-soluble phosphorus (BAP and WSP, respectively), and sediment yield. Results indicate summer management practices and grazing can impact surface water resources and potential downstream water quality. The WWF practice had greater runoff, higher sediment yields, and nutrient yields then the WWSL strategy. Likewise, grazing produced greater runoff, sediment and nutrients than ungrazed plots. The worst case scenario was grazing of the WWF pastures with 70% of precipitation lost as runoff, and the largest loss of sediment (284 kg/ha), NO3-N (124 kg/ha), BAP (380 g/ha), and WSP (38 g/ha). Loss of rainfall as runoff is considered undesirable in agriculture because such water is not available for plant utilization, and nutrient and sediment movement can create downstream water quality problems. However, catchments designed to capture eroded sediment can capture runoff, limiting the removal of runoff from a watershed, and providing immediate relief to livestock and wildlife. Depressions and micro depressions can be utilized to reduce offsite movement of runoff, sediments, and nutrients and provide a mechanism to allow recharge and storage as ground water.