Summary Roots and soils from western Nebraska fields of native and planted grasslands, and winter wheat of varied fallow‐wheat cultivation duration, were evaluated for vesicular–arbuscular (VA) mycorrhizal root infection and spore numbers and types. Increased cultivation decreased percentage mycorrhizal infection in wheat and reduced spore numbers of Glomus fasciculatus, the dominant VA mycorrhizal fungus in these soils. Spore numbers of other VA mycorrhizal fungi did not change significantly with cultivation although mean numbers of G. mosseae increased with continued wheat production. Water relations and growth were determined for greenhouse‐grown non‐raycorrhizal, G. fasciculatus‐infected, and G. mosseae‐infected wheat in wet and dry soils. Stomatal conductances were higher in mycorrhizal than in non‐mycorrhizal plants in both wet and dry treatments. Stomatal closure in‐mycorrhizal plants occurred at lower leaf water potentials (Ψ1) and after greater desiccation than in non‐mycorrhizal plants, but some leaves of G. mosseae‐infected plants showed no stomatal response to drought and continued to transpire at Ψ as low as ‐4.1 MPa. Leaf osmotic adjustment was greatest for G. fasciculatus‐infected plants. Non‐mycorrhizal and G. fasciculatus‐infected plants had equal dry wts in both wet and dry conditions. Infection by G. fasciculatus appeared to increase wheat drought tolerance while infection by G. mosseae did not.

SUMNER, DOUPNIK & BOOSALIS Multiple cropping: The intensification of cropping in time and space such as growing two or more crops on the same fi eld in a year. Sequential cropping: Growing two or more crops in sequence on the same field per year where the succeeding crop is planted after the preceding crop is harvested (double cropping, triple cropping, and quadruple cropping). Intercropping: Growing two or more crops simultaneously on the same field. Monocropping: Growing one crop on a fi eld each year. Monoculture: The repetitive growing of the same crop in the same land. More detailed explanations of other terms used in multiple cropping are given in other papers (5, 7, 74, 75, 85). Tillage in agriculture is the changing of soil conditions for crop produc tion (2). Definitions used for tillage practices are as follows: Conventional tillage: Traditional tillage system, which typically begins with a primary deep tillage operation followed by some secondary tillage for seedbed preparation (7). Conservation tillage: Any tillage practice that reduces loss of soil or water compared to unridged [soil is not mounded into a specifi c confi guration (2)] or clean tillage (85). Minimum tillage: That minimum amount of tillage required to create the proper soil condition for seed germination and plant establishment (85). Notill age, zero tillage: A method of planting crops that involves no seedbed preparation other than opening the soil for the purpose of placing the seed at the intended depth. This usually involves opening a small slit or punching a hole into the soil. There is usually no cultivation during crop production. Chemical weed control is normally used (85). Chiseling: A tillage operation in which a narrow tool is used to break up hard soil. It may be performed at other than the normal plowing depth (2). Plowing: A primary tillage operation which is performed to shatter soil with partial or complete soil inversions (2). Subsoiling: Tillage of sll;bsurface soil, without inversion, below 406 mm, to break up dense layers that �estrict water movement and root penetration (2,85). Reduced tillage systems have been established in many areas of the world and will become increasingly important in other areas where soil moisture

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