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Thursday, January 18, 2018

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690. Bear, F.E.. 1931. Soil management.. J. Wiley, N.Y..
A fairly complete text on soil management - fertility, tillage, organic matter, fertilizers; describes proper plow, moisture content, and depth to improve soil tilth; describes weeds as a potential cover crop; field study in England - free living N fixers input ~44 lb/ac/yr (est.). Azotobacter critical pH = 6.4.

1657. Doughty, J.L., F.D. Cook, and F.G. Warder. 1954. Effect of cultivation on the organic matter and nitrogen of brown soils.. Canadian J. Agr. Sci. 34:406-411.
Over 14 yr of cropping, soils lost 26% of OM and 33% of total N. Only part of the N loss is accounted for by crop removal. Some N is lost by leaching, also some gaseous loss of N other than as ammonia.

6911. Unger, P.W.. 1968. Soil organic matter and nitrogen changes during 24 years of dryland wheat tillage and cropping practices.. Soil Sci. Soc. Am. Proc. 32:427-429.
T: tillage X soil N, soil OM; total N vs. SOM

4807. Nelson, A.L.. 1950. Methods of tillage for winter wheat.. WY Agr. Expt. Sta. Bulletin 300.
Fallow/winter wheat production decreased soil N by 33% in the top 6" over 35 years. Continuous cropping lost 24% of the soil N. Crop rotations using green manure every 4th year did not decrease the loss of soil N. Average winter wheat yields (bu/ac) over 34 years for 3 rotations were: oats/rye(GM)/winter wheat/corn - 12.9; oats/peas(GM)/winter wheat/corn - 12.7; fallow/winter wheat - 13.7; oats/corn/winter wheat/rye - 13.2; oats/corn/winter wheat/peas - 14.1; oats/corn/winter wheat/fallow - 13.2. It was observed that green manure took years to break down. Tillage with an eccentric one-way increased winter wheat yields 2 bu/ac over 10 years compared to plowing. The eccentric one-way conserved moisture. Continuous cropping resulted in winter wheat yields 55% of biennial yields following fallow. Soil moisture was 3-4% lower in October after continuous cropping versus fallow.

7242. Veseth, R.. 1989. Reduced tillage for green manure legumes. STEEP Conservation Farming Update, Summer 1989, p. 3-5.
Three tillages were compared for incorporating Austrian winter pea or red clover green manure: moldboard plow plus shallow disk; shallow disk twice; no-till. At each N fertilizer rate, winter wheat yields were slightly higher with reduced tillage than with conventional tillage. A 60 lb/ac N rate substantially increased wheat yields after green manure, while the 120 N rate gave little or no yield increase. With no N fertilizer, the yield of winter wheat after both green manure crops compared favorably with yield of no-till winter wheat after a seed crop of spring peas. Legume N uptake by a following wheat crop was not affected by residue treatment, but recovery of legume N from the soil was about 10% lower with surface application than with soil incorporation. Also, wheat yields after chemically-killed green manures were consistently lower, and could not be fully recovered with fertilizer N. The mechanism of this suppression is not known.

7826. Zuzel, J.F., J.L. Pikul, and P.E. Rasmussen. 1990. Tillage and fertilizer effects on water infiltration.. Soil Sci. Soc. Am. J. 54:205-208.
Tillage and fertilization practices affect water infiltration. A long-term study at Pendleton, OR compared three tillages (plow, disk, and sweep) since 1940, and two rates of N (45 and 180 kg/ha) since 1962. Infiltration rates for plow, disk, and sweep were 17, 14, and 16 mm/h, respectively. Rates for the low and high nitrogen were 9 and 22 mm/h respectively. Results also indicate that surface sealing and soil frost are probably more important than tillage pans for infiltration. Residue cover eliminates any tillage effect on infiltration, while fertility is important in producing more crop biomass.

8374. Peterson, G.A., E. McGee, D.G. Westfall, C.W. Wood, and L. Sherrod. 1990. Crop and soil management in dryland agroecosystems.. Technical Bull. TB90-1, Dept. of Agronomy, Colorado St. Univ., Fort Collins, CO.
A large-scale field experiment was established in 1985 at 3 eastern CO locations to examine alternatives to the traditional wheat-fallow cropping system. All new treatments used no-till instead of tillage intensive management. Rotations include wheat-fallow, wheat-corn-fallow, wheat-corn-millet-fallow, and perennial grass. After five years, the more intensive cropping was giving greater grain output, nitrogen use efficiency, and water use efficiency than the wheat-fallow system. Organic matter levels also appear to be increasing. The research is also examining each strip plot at three landscape positions: toeslope, sideslope, and summit.

9764. Varvel, G.E., J.L. Havlin and T.A. Peterson. 1989. Nitrogen placement for winter wheat in three fallow tillage systems.. Soil Sci. Soc. Am. J. 53:288-292.
Increased soil water storage with increasing amounts of surface residue in winter wheat-fallow cropping systems has not consistently resulted in higher grain yields in the Great Plains. Earlier results had suggested increased amount of surface residue may increase N immobilization and limit N availability, thereby reducing potential for use of the additional stored soil water. This study was conducted to determine if N placement below the zone of organic matter or surface residue accumulation would reduce N immobilization and increase yields.

10367. Rasmussen, P.E. and C.R. Rohde. 1991. Tillage, soil depth, and precipitation effects on wheat response to nitrogen.. Soil Sci. Soc. Amer. J. 55:121-124.
Wheat yield response was measured for ten crops in a wheat-fallow rotation, with N fertilizer rates ranging from 45-180 kg N/ha. Three tillages were used: moldboard plow, offset disk, and sweep. Grain yield varied with growing season precipitation (GSP). There was a trend towards higher yield with conventional tillage when GSP was above normal. The amount of N applied for optimum yield was >135 kg N/ha with above-normal GSP and <45 kg N/ha with below-normal GSP. Excess N decreased grain yield when GSP was near normal, but not when above or below. Applied N increased straw yield curvilinearly, with little influence of tillage or soil depth. Precise selection of the amount of N to apply each year was difficult because of the strong influence of GSP.

10556. Follett, R.F. and D.S. Schimel. 1989. Effect of tillage practices on microbial biomass dynamics.. Soil Sci. Soc. Amer. J. 53:1091-1096.
Changes in microbial biomass dynamics and N cycling were studied in soils formed under grassland vegetation in western Nebraska, and farmed under wheat-fallow since 1970. Three tillage treatments were compared: no-till, stubble mulch, and moldboard plow. After 16 yr of cultivation, total N in the top 10 cm of soil had decreased to 73, 68, and 50% of native sod for the three tillages, respectively. Soil microbial biomass levels were decreased to 57, 52, and 36% for the respective tillages, compared to grass. CO2 respiration was proportional to microbial biomass, but N mineralization was not. It appeared that C availability for microbial growth declined with increased tillage intensity, which also decreased the soil's ability to immobilize and conserve mineral N.

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