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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Summer 2000 Summary: Data presented here show that a fertility program that optimizes grain yield potential will also optimize crop residue production. When re- turned to the soil, this residue can have a positive influence on soil organic matter (SOM). Nitrogen (N) fertilization enhances soil carbon (C) sequestration. Studies also show C sequestration re- sponse is superior in no-till (NT) sys- tems when compared to conventional- till (CT). Management systems that in- crease SOM levels 1) help improve soil quality, productivity, water infiltration, and fertility, 2) lower soil bulk density, and 3) reduce soil erosion. Conversion of our native grass-lands to cultivated crop land generally has resulted in a significant decline in SOM under CT. Farming methods that use mechanical tillage, such as moldboard plow for seedbed preparation or disking for weed control, contribute to releasing in- creased levels of carbon dioxide (CO2) into the atmosphere. Atmospheric CO2 levels have increased from 280 ppm (pre-industrial) to about 365 ppm to- day, with agriculture contributing to that increase. Current farming practices, such as reduced tillage, however, are helping to reduce the level of CO2 re- leased into the atmosphere. Application of plant nutrients to optimize grain yield potential generally results in in- creased crop residue production. Re- turning this residue to the soil surface by Dr. Halvorson, C.A. Reule, Dr. L.S. Murphy No-Tillage and N Fertilization Enhance Soil Carbon Sequestration Studies show that returning N treated residue to soil works better in no-till than in conventional-till systems. in reduced tillage systems is having a positive impact on SOM. Changing management practices to increase SOM levels is contributing to improved soil quality and productivity. In this article, we will discuss SOM changes that have occurred under vari- ous cropping systems as the result of several long-term studies. We'll take a look at the influence of 27 years of NT intensive cropping management on SOM and compare it, over the same pe- riod of time, to a predominantly crop- fallow CT environment. Comparisons will also be made to SOM levels in an adjacent native sod area its owner claims had not been tilled. Eleven years The first long-term N project was a dryland, NT continuous cropping study at Akron, CO. Corn was grown every other year with spring barley, winter wheat, or oat/pea hay crops substituted in alternate years. Over an 11-year span, N increased the amount of crop surface residue returned to the soil (Figure 1). SOM increased with increasing N rates. Total soil nitro- gen (TSN) in the 0 to 6-inch soil depth also increased with increasing N rates (data not shown). The increase in SOM with increasing N rates produced a sig- nificant decrease in soil bulk density at the 0 to 3-inch soil depth. 100 20 40 60 80 100 120 11 12 13 14 15 16 17 18 19 20 Dryland Annual Cropping Study - Akron Crop Residue Returned (9 crops, 11 years) Y = 12.87 + 0.129X - 0.00069X R=0.87 2 2 SOM (after 11 years) Y = 11.4 + 0.0196X - 0.0000568X R=0.85 2 2 Nitrogen Rate (lb N/A) Residue or SOM (t/acre) Figure 1. Above-ground crop residue returned to soil and changes in SOM as function of N rate in annual cropping rotation , Halvorson, et al., 11 years, Akron, CO.
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