Adverse effects of soil compaction on crop production have been recognized for many years. The objectives of this report were to briefly review the early literature, review the contributions of Dr. Howard M. Taylor (1924–1991) and co‐workers, examine the current status of soil compaction and root growth research, and identify research needs related to soil compaction and root growth. Early in his career, Dr. Taylor and co‐workers established relationships among soil strength, soil water content, and seedling emergence and root growth. These studies showed that root growth and distribution were altered to the point that water and nutrient uptake, and, hence, plant growth and yield, were reduced when soil strength reached critical levels due to natural or induced compaction. That research formed the basis for our current knowledge concerning the effects of compaction on root growth and the alleviation of compaction through soil and tillage management. Usually, not all parts of a root system are equally exposed to compaction under field conditions. Hence, because of compensatory growth by unimpeded parts of the system, only the distribution and not the total length of roots may be altered. Even if compaction limits root growth, weather events sometimes enhance or diminish the effect of root limitation on crop growth. To reduce risks in dry years and to use applied nutrients efficiently, managing soils through the use of tillage and related practices and growing of deep‐rooted crops in rotations will help avoid or alleviate compaction, thus improving root distribution and increasing rooting depth.

those methods as they have been used from the Canadian Prairie Provinces to the southern Great Plains of Successful dryland crop production in the semiarid Great Plains the United States and the resultant effects on system of North America must make efficient use of precipitation that is often limited and erratic in spatial and temporal distribution. The purpose WUE. Additionally, differences in precipitation use effiof this paper is to review research on water use efficiency and precipita-ciency (PUE) between cropping systems across the Great tion use efficiency (PUE) as affected by cropping system and manage-Plains region are identified. ment in the Great Plains. Water use efficiency and PUE increase with residue management practices that increase precipitation storage METHODS FOR INCREASING PSE, efficiency, soil surface alterations that reduce runoff, cropping se-WUE, AND PUE quences that minimize fallow periods, and use of appropriate management practices for the selected crop. Precipitation use efficiency on Tillage Effects on PSE a mass-produced basis is highest for systems producing forage (14.5 kg ha Ϫ1 mm Ϫ1 ) and lowest for rotations with a high frequency of oilseed Precipitation storage efficiency increases as tillage incrops (4.2 kg ha Ϫ1 mm Ϫ1 ) or continuous small-grain production in the tensity is reduced during the summer fallow period. The southern plains (2.8 kg ha Ϫ1 mm Ϫ1 ). Precipitation use efficiency when increased soil water storage is a result of both maintaincalculated on a price-received basis ranges from $1.20 ha Ϫ1 mm Ϫ1 (for ing crop residues on the soil surface and reducing the an opportunity-cropped system with 4 of 5 yr in forage production number of times that moist soil is brought to the surface in the southern plains) to $0.30 ha Ϫ1 mm Ϫ1 {for a wheat (Triticum as tillage intensity is reduced. Data from winter wheataestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]-fallow fallow systems at North Platte, NE (Smika and Wicks, system in the southern plains}. Throughout the Great Plains region, 1968), and Sidney, MT (Tanaka and Aase, 1987), show PUE decreases with more southern latitudes for rotations of similar fallow PSE increasing from under 25% to around 40% makeup of cereals, pulses, oilseeds, and forages. Forage systems inas tillage intensity decreased from moldboard plow to the southern Great Plains appear to be highly efficient when PUE is computed on a price-received basis. In general across the Great no-till (Fig. 1, top). Data collected at Bushland, TX, fol-Plains, increasing intensity of cropping increases PUE on both a mass-lowed a similar trend with PSE increasing from 15% with produced basis and on a price-received basis.

Understanding environmental and residue influences on decomposition and nutrient dynamics under diverse conditions is critical for efficient resource management. Our objective was to evaluate the influence of water on decomposition and N dynamics for surface and buried residues. Decomposition of alfalfa (Medicago sativa L.), grain sorghum (Sorghum bicolor [L.] Moench), and winter wheat (Triticum aestivum L. emend. Thell.) residues in fiberglass bags on the surface or buried at 129 mm in Pullman soil (fine, mixed, thermic Torrertic Paleustoll) at Bushland, TX, was measured from May 1990 to May 1991. A line-source sprinkler provided five water regimes (336, 287, 166, 60, and 5 mm) while precipitation provided 305 nun water. Decomposition coefficients (fc) were greater for alfalfa than for wheat or grain sorghum and were greater for buried than for surface residues. Rate coefficients increased linearly with water applied. The increase was greatei' for alfalfa than for sorghum and wheat. Net N mineralization occurred from alfalfa residues throughout the study. Net N immobilization was longer than 1 yr for surface wheat and sorghum and about 0.33 yr for buried residues. Both N™, (grams N immobilized per kilogram of original biomass) and Neq, (grams N immobilized per kilogram of biomass loss) were influenced by crop and placement but not water regime. The Nmax value was similar for surface wheat and sorghum residues but was 50% lower for buried wheat than for sorghum. The Neq, indicated the N requirement of microorganisms was less for buried than for surface residues. Water and residue quality interactions affecting decomposition and N dynamics should be considered in residue management strategies for soil protection and nutrient cycling.

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