COELHO, A. M.

DORAN, J. W.

SCHEPERS, J. S.

WATTS, D. G.

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Symposium no. 23 Paper no. 1372 Presentation: posterAssessing degradation of soils cultivated to irrigated coro inNebraskaCOELHO Antonio M. (1), DORAN John W. (2), WATTS Darrel G. (3) and SCHEPERSJames S. (2)(I) Ernbrapa-Maize and Sorghum Research Center, Cx. Postal 151, Sete Lagoas - Minas Gerais,Brazil(2) USDA-ARS, Univ. ofNebraska, Lincoln, Nebraska, USA(3) Dept. ofBiological Systems Engineering, Univ. ofNebraska, Lincoln, Nebraska, USAKnowledge of cause and effect relationships on crop yield variability is helpful to recommendprecision agriculture technologies. Understanding spatial variability of soil properties is importantin identifying the effects of management on soil degradation and productivity and to suggestmanagement options for enhanced sustainability. Research was conducted on two farm fields in thePlatte River Valley of south central Nebraska to determine the utility of spatial variability of soilphysical, chemical and biological properties to assess field soil degradation and crop productivitypotential. The research sites have been cultivated for over twenty-five years, under intensive soiland crop management; initially moldboard plowing and most recently using a ridge tillagemanagement system, center-pivot irrigation, and agrochemical inputs. The presence ofuncultivatedareas in close proximity to the experimental fields and on similar soil types and landscape positionswere used as reference points. The reference area for the site with a silty clay loam soil (Gibbon)has been under alfalfa (Medicago saliva L.), and at the second site (Shelton) with a sandy soil thereference area has been under perennial reed canarygrass (Pharlaris arundinacea L.). Because ofthe great difference in soil management, the reIative difference between soil properties measured inthese two reference are as and those in adjacent cropped land could be used as an indicator of soiland environmental degradation. The soil properties selected for this propose were: pH as anindicator of acidification; electrical conductivity indicating soil osmotic conditions for biologicalactivity and salinization; bulk density indicating compaction; and soil organic matter and particulateorganic matter indicating the effects of tillage and water erosion on reduction of soil organic matter.Loss of organic matter due to soil tillage, acidification associated with application of ammoniacalfertilizer, and subsoi! compaction were indicators of soi! and environmental degradation. AIso,differences in com (Zea mays L.) grain yield of 4 to 5 Mg ha-1 observed under uniform managementacross the field landscape areas indicated soi! degradation and apparent inefficiency of agriculturalproduction as indicated by loss of plant available N and associated soil acidification. Soilproperties measured in the field indicate that the systems of soi! and cropmanagement used byfarmers resulted in reduced soil quality and increased soil degradation in parts of the field whereerosion was most intense. In some lower Iying areas of the fields soil aggradation occurred due toerosional deposition of soil and associated organic matter. Additional inputs of fossil fuel-derivedenergy in irrigation and fertilizers wilI be necessary to sustain high levels of com production, whichwilllikely lead to further soil and environmental degradation.Keywords: spatial variability, soil degradation, soil quality, irrigated com872

Assessing degradation of soils cultivated to irrigated corn in Nebraska.

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