CQESTR Simulation of Management Practice Effects on Long-Term Soil Organic Carbon

Management of soil organic matter (SOM) is important for soil productivity and responsible utilization of crop residues for additional uses. CQESTR, pronounced “sequester,” a contraction of “C sequestration” (meaning C storage), is a C balance model that relates organic residue additions, crop management, and soil tillage to SOM accretion or loss. Our objective was to simulate SOM changes in agricultural soils under a range of climate and management systems using the CQESTR model. Four long-term experiments (Champaign, IL, \u3e100 yr; Columbia, MO, \u3e100 yr; Lincoln, NE, 20 yr; Sidney, NE, 20 yr) in the United States under various crop rotations, tillage practices, organic amendments, and crop residue removal treatments were selected for their documented history of the long-term effects of management practice on SOM dynamics. CQESTR successfully simulated a substantial decline in SOM with 50 yr of crop residue removal under various rotations at Columbia and Champaign. The increase in SOM following addition of manure was simulated well; however, the model underestimated SOM for a fertilized treatment at Columbia. Predicted and observed values from the four sites were signifi cantly related (r2 = 0.94, n = 113, P \u3c 0.001), with slope not signifi cantly different from 1. Given the high correlation of simulated and observed SOM changes, CQESTR can be used as a reliable tool to predict SOM changes from management practices and offers the potential for estimating soil C storage required for C credits. It can also be an important tool to estimate the impacts of crop residue removal for bioenergy production on SOM level and soil production capacity

On the Structure of the Fusion Ideal

We prove that there is a finite level-independent bound on the number of relations defining the fusion ring of positive energy representations of the loop group of a simple, simply connected Lie group. As an illustration, we compute the fusion ring of $G_2$ at all levels

Wheat Straw Decomposition in the Field

Wheat (Triticum aestivium) varieties 'Nugaines' and 'Lemhi' were grown on Portneuf silt loam soil with three nitrogen and three irrigation treatments in 1967. After harvest, 84 kg N/ha was applied to half of each plot before plowing. Uniform straw samples were enclosed in fiberglass cloth bags and buried in the plots September 7. The straw placed in N-treated plots received sufficient N in solution to increase the straw N from about 0.29 to 1.5%. Straw samples were recovered November 15, after the soil had cooled below 4C, and at three later sampling dates to October 3, 1968, after a bean crop (Phaseolus spp.) was harvested. Weight loss and total N were determined on all samplings and total C on the first sampling. Decomposition was greater with N than without it for the November sampling and the March sampling for Nugaines but not at other samplings for both varieties. The weight of N in both N-treated straw varieties decreased 55% by November 15, while in the non-N-treated Nugaines and Lemhi straw, N weight increased 12 and 32%, respectively, by March 22. Later, N moved out of all the straw samples when the N percentages were much lower than the theoretical equilibrium value

Microbiological Quality of Surface Drainage Water from Three Small Irrigated Watersheds in Southern Idaho

The irrigation waters applied to and the surface drainage waters leaving three small watersheds in southern Idaho were analyzed for coliforms and other microorganisms and for biochemical oxygen demand (BOD). Numbers of coliforms and fecal coliforms tended to be greater in the drainage than in the irrigation water, but the differences were generally within the confidence limits for Most Probable Numbers analyses. Fecal streptococci numbers were higher in the drainage than in the irrigation water on two of the three small watersheds. The numbers of fecal streptococci and microorganisms incubated at 20C were higher in the drainage than the irrigation water; otherwise, the bacteriological quality of the irrigation water was not significantly changed by irrigation use. BOD in the drainage water samples averaged 4 mg/liter oxygen demand compared with 2 mg/liter oxygen demand in the irrigation water

Influence of Residual Nitrogen on Wheat Straw Decomposition in the Field

Plant material decomposition appears to be mainly controlled by the C/N ratio of the plant material under soil moisture, temperature, and aeration conditions that support plant growth in the field. Harmsen and VanSchreven (4) reported, "Numerous earlier papers were devoted to the study of this problem .... Fairly close agreement was obtained by all these investigators as to the N content limits of the added material, below which no N mineralization may be expected. This is 1.5 to 2.0 per cent of the dry matter, corresponding to a C/N ratio of 20 to 25." Similar values were also reported by Broadbent (2) from laboratory studies; and Allison (1), in a recent review, cited several reports that are in general agreement

Influence of Silica and Nitrogen Contents and Straw Application Rate on Decomposition of Gaines Wheat Straw in Soil

'Gaines' and 'Nugaines' varieties of soft white winter wheat (Triticum aestivum) yield straw ranging up to about 7 tons per acre (2). Growing row crops such as dry edible beans (Phaseolus vulgaris) or sugarbeets (Beta vulgaris) following such heavy straw production poses special management problems. Straw layers that result from plowing down a large amount of straw may result in reduced bean yields (supposedly because of nitrogen immobilization), abnormal sugarbeet root growth, and tillage and water movement problems. Much of the tremendous acreage of the irrigated wheat grown in the Pacific Northwest is in rotation with sugarbeets, potatoes, beans and other crops. Therefore, straw residue management is a major problem with great economic implications

The relationship of particle size and nitrogen content to decomposition of wheat straw in soil

Straw samples of different particle size and N content were selected from three spring wheat (Triticum aestivum) varieties; added to Walla Walla, Palouse, and Portneuf silt loam soils at 0.5 and 2.0% rates; and incubated. At the 0.5% addition rate, straw samples containing 0.2 to 0.7% N decomposed at the same rate. When 2.0% straw was added to soil, the decomposition rates increased with increasing N percentage. The N- supplying capacity of the soil apparently influenced decomposition at the higher straw rates. After incubation, considerable nitrate was found in the soil with 0.5% straw but little was found in the soil with 2.0% straw. Different particle sizes of straw with the same N contents decomposed at approximately the same rate. Soil nitrate concentrations were lower for each successively smaller straw particle size after incubation

Microbiological Quality of Subsurface Drainage Water From Irrigated Agricultural Land

Irrigation and subsurface drainage waters sampled from an 82,150-hectare (203,000-acre) irrigation district in southern Idaho were evaluated for bacteriological quality. The soils in the district are wind deposited over fractured basalt, calcareous, and have a pH near 7.8. Drainage, where needed, is provided by horizontally mined tunnels or by tile drains connecting shallow relief wells that flow the year around. For the 12 months ending September 30, 1969, a 2-meter (6.5-foot) depth of water for the entire irrigation tract was diverted, and 50% of the water passed through the soil becoming subsurface drainage. The irrigation water and seven subsurface drains were sampled at 2-week intervals during the summer of 1969. Coliform, fecal streptococci, starch hydrolyzers, and bacteria able to grow at temperatures from 0 to 55C were counted. The diverted irrigation water contained from 140 to 3,300 coliform per 100 ml, but 86% of the subsurface drainage samples contained 5 or fewer conforms per 100 ml. Numbers of other microorganisms were also low in the drainage waters. The outflow samples were oxygen saturated and the temperatures were 13.0 ± 1.1C for all samples. Percolation through the soil improved the water quality almost to domestic water standards

The Influence of Straw Application Rates, Plowing Dates, and Nitrogen Applications on Yield and Chemical Composition of Sugarbeets

Fertilizer N applied at ever-increasing rates sometimes accumulates in the soil. The practice of fertilizing grain straw with N to stimulate decomposition is questionable, but decomposition of straw immobilizes N that must be compensated for in fertilizing the succeeding crop. Too much N decreases the sucrose content of sugarbeets and decreases sucrose recovery. Experiments were conducted to determine the relative value of early and late straw applications, plowing with N applied in the fall or spring, and the amount of N needed to compensate for straw applications in obtaining optimum beet and sucrose yields with maximum quality. Sugarbeets (Beta vulgaris L.) were grown following winter wheat (Triticum aestivum L., var. 'Nugaines') in 1970 and 1971 on a Portneuf silt loam soil near Kimberly, Idaho. Straw was applied to the beet plots at rates of 6.7, and 13.4 metric tons/ha, and the plots were plowed either in early September or mid-November. Nitrogen was applied at 67 kg N/ha in the fall and at 67 and 134 kg N/ha in the spring. The treatments were arranged in a split-split lot design with 4 replications. Control plots were used with all experiments. N fertilization increased beet, top, and sucrose yields, as well as amino N, Na, K concentrations, and impurity index. It decreased the sucrose percentages of the beets. Straw applications decreased beet, top, and sucrose yields, Na and amino N concentrations, and impurity index, but they did not influence K content of the beets. Early plowing increased sucrose percentage and yield and decreased Na, K, and impurity index. Interactions between straw applications and plowing dates were significant for sugarbeet and beet top yields. Approximately 7.5 kg N fertilizer per metric ton of straw were required to compensate for the deleterious effects of the straw