Rotational Cropping Sequence Affects Yield of Corn and Soybean
There are numerous reports of the beneficial effects of rotating corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. However, few studies have been specifically designed to document the important corn‐soybean rotation effect. The objective of this study was to determine the impact of various corn and soybean cropping patterns on the yield of both crops. The 9‐year field study conducted at two locations was managed for maximum production. Cropping sequences consisted of: continuous monoculture with the same cultivar; continuous monoculture with cultivars alternated; annual rotation of the two crops; and 1, 2, 3, 4, and 5 yr of monoculture following 5 yr of the other crop. Annually rotated corn yielded 10% better, and first‐year corn yielded 15% better than corn under monoculture. Annually rotated soybean yielded 8% better, and first year soybean yielded 17% better than soybean under monoculture. With monoculture of either crop, alternating two different cultivars annually resulted in the same yield as continuous cropping of just one cultivar. There were differences in the response of the two crops to increasing years of monoculture: the lowest corn yield was from second year corn; the lowest soybean yield was from extended monoculture. Total corn dry weight was affected by cropping sequence but soybean dry weight was not. Our data suggest that, from a yield standpoint, a superior cropping sequence for Minnesota would include at least three, and possibly more crops. 
The Effects of Soil Moisture Stress at Different Stages of Growth on the Development and Yield of Corn
Moisture stress prior to silking reduced grain yield by 25%, moisture stress at silking reduced grain yield by 50% and moisture stress after silking reduced grain yield by 21%. The interactions between different growth stages were not statistically significant. 
Planting Patterns and Radiation Interception, Plant Nutrient Concentration, and Yield in Corn
The upper leaves of corn (Zea mays L.) are radiation‐saturated while the lower leaves, the prime source of carbohydrates for nutrient uptake by roots, are radiation‐starved. This study was conducted to determine the degree to which planting patterns could influence radiation interception by layers in the canopy, plant nutrient concentration, and yield in corn. Corn was planted in the field in a high‐yielding environment on a Drummer silty clay loam (finesilty), mixed, mesic, Typic Haplaquoll) in 0.38 m single rows, 0.76 m twin rows, 0.76 m single rows, 1.14 m twin rows, and 1.52 m twin rows with 0.13 m between pairs of twin rows. Interception of solar radiation shortly after silking was generally similar for all the planting patterns except for the 1.52 m twin row spacing which intercepted 10% more incident radiation with lower rather than upper leaves compared to the other planting patterns 3 h before solar noon, but allowed 7% more incident radiation to strike the soil surface compared to the narrow row spacings (0.38 ‐ 0.76 m) at solar noon. Planting pattern had no consistent effect on nutrient concentration in the grain, stover, or cob. Grain yields averaged 9.7 Mg ha−1 for the 1.52 m twin planting pattern and 11.7 Mg ha−1 for the other planting patterns. In conclusion, wide row spacings resulted in a partial redistribution of radiation from the upper to the lower leaves but allowed more radiation to strike the soil surface, did not affect plant nutrient concentration, and decreased yield. 
A Study on Effects of Planting Dates on Growth and Yield of 18 Corn Hybrids (Zea mays L.)
In this study 18 new corn varieties consist of 15 foreign early and mid-mature single cross hybrids and 3 Iranian commercial hybrids (KSC704, KSC647and DC370) were evaluated at two sowing date (5 and 20 June) based on RCBD with 3 replications at Khorasan Razavi Agricultural Research Centre, Mashhad, Iran on 2009. This study showed that among all hybrids, EXP1 (16.03 ton/ha) and OSSK617 (15.51 ton/ha) had the highest yields in early planting (5 June) and EXP1 (16.52 ton/ha) and KDC370 (16.22 ton/ha) produced the highest, yields in late planting (20 June). Results of this experiment also indicated that yield component such as 300 kernel weight, kernel no. per row, kernel depth and ear length were adversely affected in delay planting condition. Delay planting reduced 300- kernel weight, kernel no. per row, kernel depth and ear length. Results of cluster analysis using Wards’ method divided the corn hybrids into 4 different clusters (low intra-group and high extra-group similarities). From the results of cluster analysis it is recommended to make crosses among genotypes in Clus1 (ZP434, BC582 and EXP2 hybrids) and Clus4 (ZP684, SIMON and KSC647) in breeding programmes. Classifying genotypes according to their agronomic traits with sophisticated multivariate techniques could reduce the time period and expenditure for crop improvement. 
Correlation and Path Coefficients Analysis between Morphological Characteristics and Conservable Grain Yield of Sweet and Super Sweet Corn (Zea Mays L. var. Saccharata) Varieties
In order to evaluate the effects of planting methods on morphological traits, yield and yield components of sweet and super sweet corn varieties, an experiment was conducted at Khorasan Razavi Agricultural and Natural Resources Research center, Mashhad, Iran in 2012. In this research three planting method (one row raised bed, two row raised bed and furrow planting), sweet corn varieties (Chase, Temptation, KSC403su and Challenger), was laid out in factorial design based on randomized complete block design with three replications. The results of this study showed that different planting methods had significant effects on morphological traits such as plant height, ear height, ear leaf area, relative growth rate, 1000-grain weight, ear diameter, number of ear per plant, grain depth, conservable grain yield and plant harvest index at the P<.01 level. Moreover, results showed that different varieties had significant differences among traits such as the number of ear per plant, ear diameter, grain percentage, cob percentage, 1000-grain weight, conservable grain yield and harvest index. The results of correlation coefficient analysis also indicate highly significant correlation between conservable grain yield and all measured traits except for plant height, ear height, relative growth rate, ear diameter, and the number of ear per plant at the P<.01 level. The results of stepwise regression method analysis and path coefficient showed that conservable grain yield was affected by three traits of 1000-grain weight, ear diameter and number of ear per plant. Furthermore, these three traits indicate high and significant regression coefficient on conservable grain yield, respectively. Results of path coefficient analysis indicated that all traits positively affect conservable grain yields. Therefore, the measured traits like 1000-grain weight, ear diameter and the number of ear per plant had the highest direct effect on conservable grain yield. According to this study, selection for 1000-grain weight, ear diameter and number of ear per plant can led to improve conservable grain yield. 
 Crookston, R.K., Kurle, J.E., Copeland, P.J., Ford, J.H. and Lueschen, W.E., 1991. Rotational cropping sequence affects yield of corn and soybean. Agronomy Journal, 83(1), pp.108-113.
 Denmead, O.T. and Shaw, R.H., 1960. The Effects of Soil Moisture Stress at Different Stages of Growth on the Development and Yield of Corn 1. Agronomy journal, 52(5), pp.272-274.
 Ottman, M.J. and Welch, L.F., 1989. Planting patterns and radiation interception, plant nutrient concentration, and yield in corn. Agronomy Journal, 81(2), pp.167-174.
 Beiragi, M.A., Khorasani, S.K., Shojaei, S.H., Dadresan, M., Mostafavi, K. and Golbashy, M., 2011. A study on effects of planting dates on growth and yield of 18 corn hybrids (Zea mays L.). Journal of Experimental Agriculture International, pp.110-120.
 Rahmani, A., Alhossini, M. and Khorasani, S. (2014) “Correlation and Path Coefficients Analysis between Morphological Characteristics and Conservable Grain Yield of Sweet and Super Sweet Corn (Zea Mays L. var. Saccharata) Varieties”, Journal of Experimental Agriculture International, 4(11), pp. 1256-1267. doi: 10.9734/ajea/2014/7031.