TITLE: Canola Production as Influenced by Previous Crop and Tillage System MAJOR PROFESSORS: Dr. Michael Schmidt and Dr. Brian Klubek This study was conducted to compare the profitability of winter canola versus winter wheat following corn and soybean under a reduced till and no till regime. Yield of double crop soybean production behind canola vs. wheat was also studied. The experiment was designed as a complete factorial with a split-split-split plot arrangement using 4 replications. Corn/soybean served as the main effect. Tillage was the sub-plot, and winter canola/wheat served as the sub-sub-plot. Two varieties each of canola and wheat were tested as sub-sub-sub plot. Fall stand, seed yield, and double crop soybean yield were measured for all plots. Interactions between either pair of canola or wheat varieties with previous crop or tillage system were not detected either season. Canola produced a higher yield after a previous crop of corn than after a previous crop of soybean in 2005-2006. In 2007-2008, the yield of canola after soybean was higher however this difference was not significant. No influence of previous crop on wheat yield was detected either season. The influence of tillage on canola and wheat yield was inconsistent across seasons. Canola produced a higher yield under reduced till in 2007-2008, but not in 2005-2006. In 2005-2006, wheat produced a higher yield under no-till and a higher yield under reduced till in 2007-2008. In 2007-2008, a significant interaction between previous crop and tillage system was detected for both canola and wheat. Canola yield was significantly reduced by no-till after corn but not so by no-till after soybean. Wheat yield was significantly lower following corn no-till than following soybean no-till, however, there was no difference in wheat yield following corn or soybean under reduced till. The yield of double crop soybean did not differ following winter canola or winter wheat either season, however in 2005-2006, yield was higher following corn after either canola or wheat. The double crop soybean yield was 1,421 hg/ha in 2005-2006 and was 3,161 kg/ha in 2007-2008. The results herein indicate that canola and wheat can be profitably grown behind either corn or soybean and under either a reduced till or a no-till system. However, these results are inconclusive as to which combination of previous crop or tillage system should be recommended for either winter crop. It does appear that there is a greater concern establishing a canola stand under a no-till system. Canola provided greater gross revenue over that of wheat both seasons, even after considering the additional canola seed and nitrogen costs. When combined across seasons, canola had a mean yield of 3,838 kg/ha and a mean revenue of $1,236/ha. Wheat had a mean yield of 5,511kg/ha and a mean revenue of $939/ha. The seed and nitrogen cost differential was computed at $70. Thus, the canola crop provided revenue that was 25% higher per hectare than the wheat crop.

Tillage operations disrupt the soil structure resulting in aggregates of various sizes and altered bulk density. Moreover, tillage influences soil carbon pools and many other soil physical properties. The objectives of this study were to determine, in various South African soils under different tillage systems, the following. (1) Amount of aggregate-associated soil organic carbon (SOC), (2) soil compressibility, and (3) relationship between compressibility, texture and the aggregate-associated SOC. The soil samples used in this study were collected from six different sites in Eastern Cape Province, South Africa. Soil samples were taken from conventional tillage (CT) and no-till (NT) land. To keep the soil aggregates intact sampling was done using a spade and carefully carried to the laboratory in rigid containers. For SOC determination, treatments were the two tillage systems, CT and NT, and four aggregate sizes. The experimental design was completely randomized design with a factorial layout and was replicated three times. Aggregate-associated SOC was determined using Walkley-Black method. Proctor compaction test was used determine the dry bulk density with varying moisture content and consequently the maximum bulk density (MBD) and critical water content (CWC). The aggregate-associated SOC content differed with tillage system and was significant higher (p < 0.05) in CT than NT. The amount of aggregate-associated SOC was 1.67 times higher in CT than NT plots. The MBD ranged between 1.77 g/cm3 and 10.27 g/cm3 and the CWC ranged from 9.1 percent to 10.3 percent. The higher amounts of SOC in CT were attributed to the annual crop residue returns while the lower amounts of SOC in the NT fields were due to grazing. Therefore, tillage influenced the amount of aggregate-associated organic carbon irrespective of the resulting size of the aggregate. The positive relationship between tillage and aggregate-associated SOC challenges the conversion of land to no-till for carbon sequestration. The overall gradient for correlation between the MBD and CWC was negative with r2 = 0.23 and a p value of 0.0076. The compressibility curves indicated higher values under CT if the texture class was silt clay.

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Farmers are always looking for ways to increase yields and profits and no-tillage may be a way to achieve this goal. However, a comprehensive study of the performance of no-tillage yields relative to conventional tillage yields and their net returns is lacking. This study evaluated the potential factors that influence differences in conventional tillage and no-tillage yields and net returns as explained by such factors as time, crop, precipitation, soil texture and geographic region. Data were collected from 442 paired tillage experiments growing corn, soybeans, cotton, oats, wheat and sorghum published in three refereed journals. Data were evaluated using a mixed model and logit model respectively, to evaluate differences in mean yields and downside risk with no-tillage compared to tillage. Sorghum and wheat were found to have higher no-tillage yields relative to tillage. No-tillage was also found to outperform conventional tillage in the southern United States with just the opposite occurring in the northern U.S. A silty soil was also found to reduce no-tillage yields. Several factors were found to decrease the chance of downside risk with no-tillage, they were sorghum, sandy soil, Northern Crescent, Northern Great Plains, Prairie Gateway and Southern Seaboard regions. Two factors that increased the chance of lowered no-tillage yields were increased rainfall and length of use of no-tillage. Differences in mean net returns and downside risk were evaluated using a mixed model and logit model. Results showed that no-tillage was more profitable than conventional tillage in the Mississippi Portal region, but less profitable in the Prairie Gateway. Net returns were lower for no-tillage wheat and soybeans when produced in a clay soil. Cotton grown in sand had higher no-till net returns, but increased rainfall decreased cotton net returns. A logit model showed certain factors decreased the probability of lower no-tillage net returns. There was less downside risk with wheat grown under no-tillage as well as less downside risk in the Southern Seaboard region and when no-tillage was used on a clay soil. There were factors that increased the probability of lower no-tillage net returns; increased precipitation, Northern Great Plains, Prairie Gateway and Basin & Range regions.