RESULTS AND DISCUSSION Impact of Rotation on Yield and Economic Performance in Winter Canola-Summer crops Cropping Systems Suresh Kumar*, Udai R. Bishnoi, and Ernst Cebert Department of Natural Resources and Environmental Sciences, Alabama A&M University, Normal, AL 35762 ABSTRACT In the southeast US, winter wheat as a double crop has proved to be economically profitable and beneficial for soil management to the farmers. Winter canola (Brassica napus L.) also has similar potential but its suitability as a double and in rotation with summer crops has not been evaluated. Therefore, performance of winter canola in rotation and as a double crop with soybean, corn, sorghum, and cotton were evaluated for two years. Results showed that effect of rotation on plant density during both the years was significant. Rotational effects on number of pods per plant were non-significant than canola grown as fallow in 2003 but not in 2004. Canola grown after soybean produced significantly higher seed yield in 2003 (2739 kg ha-1) and 2004 (3129 kg ha-1) than after other crops except corn (2938 kg ha-1) and fallow (2876 kg ha-1). Planting canola after fallow gave significantly the lowest economic returns during both the years. Canola gave significantly higher economic returns when planted after corn ($1237) and cotton ($1169) than soybean-canola and sorghum-canola and fallow-canola rotations in 2003. In 2004 also, canola planted after cotton gave significantly higher economic returns per hectare ($1442) which was equal to soybean-canola ($1393) than corn-canola, sorghum-canola, and fallow-canola cropping systems. INTRODUCTION Oilseed rape (Brassica related species) is now the second largest oilseed crop in the world and has passed peanut, sunflower and cottonseed in world’s oil supply. Spring type B. napus is produced in Canada and northern Europe. In southeastern United States, where winters are mild, B. napus can be grown as a fall-planted winter crop; however, its production in the southern US is relatively rare. Except for wheat and to some extent rye and barley, no other winter crop particularly a cash crop like canola has been tried in rotation with major southeastern summer (cotton, peanut, corn, and soybean) crops. Crop diversification provides more control opportunities and disrupts life cycles of weeds that are crop mimics (Anderson, 1997). Guy (1999) observed that canola provides greater production potential, reduced disease levels and minimize soil erosion in subsequent winter wheat crops when compared to wheat or barley. Cropping systems in the Northern Great Plains (NGP) have evolved from wheat–fallow rotations to diversified cropping sequences. Consequently, weed communities have changed and in some cases, become resistant to commonly used herbicides, thus increasing the complexity of managing weeds (Derksen et al., 2002). Producers in the semiarid NGP have been extending and diversifying their crop rotations by including broadleaf crops such as chickpea, dry pea, lentil, canola, and mustard (Gan, et al., 2003). In southeastern US, like winter wheat, double cropping of winter canola with summer crops has the potential for increased profits, improved cash flow, and rotational benefits (Raymer et al., 1990). In a region dominated by winter wheat, the acceptance and production of another crop like canola require that it suits the cropping system agronomically and economically and benefits the farmers. Such information on canola rotation with summer crops is not available, therefore, this study was conducted. OBJECTIVES To determine the rotational effects of summer (soybean, corn, sorghum and cotton) crops on plant density, pods and yield of winter canola and (2) To evaluate the yield and economic return from winter canola when rotated with summer crops. MATERIAL AND METHODS The experiments were conducted for two (2002-2003 and 2003-2004) crop growing seasons on Decatur silty clay in Hazel Green, Alabama. The experiment consisted of five treatments (four summer crops: soybean, corn, sorghum, and cotton and canola) planted in a randomized complete block design with four replications and each cropping system was in place each year. The plot size for each summer crop (Fig. 1) and canola was 1.06 m × 12.16 m. Summer crops were planted on May 11, 2002 at recommended seed rates and canola after the harvest of these crops, on September 28, 2002. Similarly, during 2003, summer crops were planted on May 10, 2003 and canola was planted on Oct 2, 2003 which was harvested in June 2004. The experiment consisted of five cropping systems: i) Soybean–Canola–Soybean–Canola, ii) Corn-Canola-Corn-Canola, iii) Sorghum-Canola-Sorghum-Canola, iv) Cotton-Canola-Cotton-Canola, and v) Fallow-Canola-Fallow-Canola. Lime, N, P, and K were applied to all the above crops planted in rotations according to the soil test recommendations. To control weeds, Trifluralin and Sethoxydim herbicides, each at 2.1 lit ha-1 were applied as pre- and post-emergent, respectively. Data on rotational effects of summer crops on canola were collected for the following plant parameters: Plant density From each plot, plants were counted from two randomly selected rows, each two-meter long at physiological maturity. RESULTS AND DISCUSSION Rotational effect on plant density In this study, the highest plant density due to rotation was observed in canola planted after soybean, which gave highest seed yield over other summer crops. The plant density per two m row in canola planted after soybean was 40.75 cm in 2003 and 39.50 cm in 2004 growing seasons; however the differences were significant only in 2004 (Table 1). Angadi et al., (2003) observed that the decrease in population to 10 and 5 plants m-2 reduced seed yield by 42 to 92% of 80 plant m-2. Rotational effect on pods per plant There was no significant difference among pods per plant when canola was planted after summer crops and fallow in 2003 (Table 1). In contrast, the rotational differences were noticed during 2004 when canola planted after soybean produced significantly highest pods per plant than canola planted after cotton but not when planted after corn, sorghum, or fallow. The increase in the number of pods in canola planted after soybean has been corroborated by Angadi et al. (2003) who observed that there was a strong effect of population density on the pods on primary and secondary branches. In this study, the plant structure adapted to the canola planted after summer crops and fallow by increasing pods per plant at lower plant populations. Rotational effect on canola seed yield The rotational effects on seed yield were significantly higher in canola planted after soybean (2739 kg ha-1) than canola planted after cotton and sorghum in 2003; however, there was no significant difference in yield in canola planted after soybean, corn, and fallow (Table 1). During 2004, canola planted after soybean gave the highest seed yield of 3129 kg ha-1, followed by corn, fallow, sorghum, and cotton. Such rotational effects have been observed by Harris et al., (2002) who reported that wheat yielded 11% more grain when grown after canola than wheat grown after wheat. Guy, (1999) has also observed that wheat yields were at least 25% less following wheat than wheat grown after canola, mustard, crambe, or pea. Economic Analysis The financial returns varied in both the years depending upon the prices received by the farmers as per the US price index (Fig. 1). During 2003, significantly higher economic returns of $1237 and $1169 ha-1 (Table 1) were observed when canola was planted as a double crop after corn and cotton, respectively, over soybean and sorghum. In the second year, canola-cotton rotation gave highest economic returns ($1442 ha-1) which was equal to soybean-canola and was significantly higher than corn-canola and sorghum-canola rotations. CONCLUSIONS Canola plant density increased when rotated after soybean and corn, which also increased the number of pods per plant in comparison to canola planted after cotton. 2. Canola produced higher yield when planted after soybean and corn than after sorghum and cotton. 3. The cropping systems of canola grown as a double crop provided significantly higher economic returns when planted after corn and cotton than soybean and sorghum in 2003. In 2004, canola planted after cotton gave significantly higher economic returns than when planted after corn and sorghum. REFERENCES Anderson, R.L. 1997. Cultural systems can reduce reproductive potential of winter annual grasses. Weed Technol. 11:608–613. Angadi S. V., H. W. Cutforth, B. G. McConkey and Y. Gan. 2003. Yield Adjustment by Canola Grown at Different Plant Populations under Semiarid Conditions. Crop Science 43:1358-1366. Derksen, D. A., Randy L. Anderson, R. E. Blackshaw, and Bruce Maxwell. 2002. Weed Dynamics and Management Strategies for Cropping Systems in the Northern Great Plains. Agron. J. 94: 174-185.  Gan, Y.T., P.R. Miller, B.G. McConkey, R.P. Zentner, F.C. Stevenson, and C.L. McDonald. 2003. Influence of diverse cropping sequences on durum wheat yield and protein in the semiarid northern Great Plains. Agron. J. 95:245–252. Guy, S. O. 1999. Crop residue and durability effects of brassicas and other crops on winter wheat. Proceedings of the 10th International rapeseed Congress, Canberra, Australia. Harris, R. H., G. J. Scammell, W. J. Müller, and J. F. Angus. 2002. Crop productivity in relation to species of previous crops and management of previous pasture. Australian Journal of Agricultural Research 53(11) 1271 – 1283. National Agricultural Statistics Service. 2004. Crops and Plants: data and statistics. Raymer, P. L., D. L. Auld, and K. A. Mahler. 1990. Agronomy of canola in the United States. p. 25–35. In: F. Shahidi (ed.), Canola and rapeseed: Production, chemistry, nutrition, and processing technology. Van Nostrand Rhienhold, New York. SAS Institute. 1999. The SAS system for Windows. Version 8.2. SAS Inst., Cary, NC. Table 1. Plant density, pods per plant, and seed yield of canola after rotation with summer crops. Plant density Pods per plant Seeds yield (kg ha-1)  Treatment† 2003 2004 Sy-C 40.75a 39.50a 196ns 223a 2739a 3129a M-C 39.00ab 37.50a 206ns 194ab 2570a 2938ab S-C 33.50b 32.00b 202ns 210ab 2440b 2650bc G-C 33.00b 32.25b 194ns 192b 2445b 2521c F-C 32.50b   216ns 211a 2557ab 2876abc *, ** Significant at the 0.05 and 0.01 probability levels, respectively; ns, non-significant. †Sy-C, soybean-canola; M-C, corn-canola; S-C, sorghum-canola; G-C, cotton-canola; F-C, fallow-canola. Corn Sorghum Soybean Cotton Fig.1. Summer crops grown in rotation with canola. Table 2. Economic returns from summer crops - canola double cropping systems. 2002-2003 2003-2004 Yield Returns Total returns Treatment† (kg ha-1) (US $ ha-1)‡ Sy/C 1755/2739 357/639 996b 2384/3129 621/772 1393ab M/C 5949/2570 637/600 1237a 6978/2938 645/725 1370b S/C 4368/2440 394/570 964b 4760/2650 430/654 1084c G/C 624/2445 598/571 1169a 802/2521 820/622 1442a F/C 0/2557 0/597 597c   0/2876 0/707 707d *, ** Significant at the 0.05 and 0.01 probability levels, respectively; ns, non-significant. †Sy-C, soybean-canola; M-C, corn-canola; S-C, sorghum-canola; G-C, cotton-canola; F-C, fallow-canola. Number of pods per plant The total number of pods from five randomly selected plants per plot from each replication was counted at physiological maturity. Final canola seed yield The four center rows from six-row plots of canola were harvested by combine. Seeds were weighed and passed through standard sieves to obtain marketable seed quality. Results were expressed as seed yield in kg ha-1 adjusted to 8.5% moisture content. Summer crops yield The yield of summer crops (soybean, corn, sorghum, and cotton) adjusted to 13.0, 15.5, 12.0, and 12.0 % moisture content, respectively, was expressed as kg ha-1. Economic evaluation To calculate cost to return ratios per ha for canola and summer crops, economic returns for the crops were calculated by multiplying seed yield by the prices received by farmers per hectare as per the US price index (National Agricultural Statistics Service, 2004). Prices of soybean, corn, sorghum, and cotton were $ 20.37, 10.71, 9.03, and 95.81 per 100 kg in 2002-2003 and $ 26.06, 9.25, 9.03, and 102.2 per 100 kg in 2003-2004 and canola @ $ 23.34 and 24.66 per 100 kg in 2003-2004, respectively. Data collected were analyzed using analysis of variance with SAS system (SAS Institute, 1999) and means were separated by Tukey’s test.