Castor (Ricinus communis L.) is one of the oldest cultivated crops, but currently it represents only 0.15% of the vegetable oil produced in the world. Castor oil is of continuing importance to the global specialty chemical industry because it is the only commercial source of a hydroxylated fatty acid. Castor also has tremendous future potential as an industrial oilseed crop because of its high seed oil content (more than 480 g kg−1), unique fatty acid composition (900 g kg−1 of ricinoleic acid), potentially high oil yields (1250–2500 L ha−1), and ability to be grown under drought and saline conditions. The scientific literature on castor has been generated by a relatively small global community of researchers over the past century. Much of this work was published in dozens of languages in journals that are not easily accessible to the scientific community. This review was conducted to provide a compilation of the most relevant historic research information and define the tremendous future potential of castor. The article was prepared by a group of 22 scientists from 16 institutions and eight countries. Topics discussed in this review include: (i) germplasm, genetics, breeding, biotic stresses, genome sequencing, and biotechnology; (ii) agronomic production practices, diseases, and abiotic stresses; (iii) management and reduction of toxins for the use of castor meal as both an animal feed and an organic fertilizer; (iv) future industrial uses of castor including renewable fuels; (v) world production, consumption, and prices; and (vi) potential and challenges for increased castor production.

Growing conditions in the U.S. Midsouth allow for large soybean [Glycine max L. (Merr.)] yields under irrigation, but there is limited information on planting dates (PD) and maturity group (MG) choices to aid in cultivar selection. Analysis of variance across eight (2012) and 10 (2013) locations, four PD, and 16 cultivars (MG 3-6), revealed that the genotype by environment (G×E) interaction accounted for 38 to 22% of the total yield variability. Stability-analysis techniques and probability of low yields were used to investigate this interaction. Planting dates were grouped within early-and late-planting systems. Results showed that MG 4 and 5 cultivars in early-planting systems had the largest average yields, whereas for late-planting systems, late MG 3 to late MG 4 cultivars had the largest yields. Least square means by MG within planting systems at each environment showed that MG 4 cultivars had the greatest yields or were not signi cantly di erent from the MG with the greatest yields in 100% of the environments for both early-and late-planting systems. Yields of MG 5 cultivars were similar to those of MG 4 in 100% of the environments with an early planting but only in 20% of the environments with a late planting. e MG 3 cultivars were the best second choice for late plantings, with similar yields to MG 4 cultivars in 55 to 75% of the environments. ese results have profound implications for MG recommendations in irrigated soybean in the U.S. Midsouth and indicate the need to reconsider common MG recommendations.

Planting date is one of the main factors affecting soybean (Glycine max [L.] Merr.) yield. Environmental conditions in the US Midsouth allow for planting dates from late March through early July, and maturity groups (MGs) ranging from 3 to 6. However, the complexity of interactions among planting date, MG, and the environment makes the selection of an optimum MG cultivar difficult. A regional 3‐yr study, conducted at eight locations with latitudes ranging from 30.6 to 38.9°N, planting dates ranging from late March to early July, and MGs 3 to 6, was used to examine the relationship between relative yield and planting day. The data indicated that yield was dependent on the location and MG choice. There was a quadratic response of relative yield to planting day in six out of the eight locations studied for MG 3 cultivars, and in five locations for MG 4 cultivars. On the other hand, MG 5 and 6 cultivars were more likely to have a negative linear relationship, with a quadratic response in only two of the eight locations. Optimum planting dates that maximized yield were dependent on the location and MG combination and ranged from 22 March to 17 May. Delaying planting dates from mid May to early June reduced yields by 0.09 to 1.69% per day, with the rate of decline greatest at the southern‐most locations. Overall, MG 4 cultivars maximized yield or were not statistically different from the highest yielding MG at most locations and planting dates.

A greenhouse experiment used a replacement series design to compare the vegetative growth 6 wk after emergence in pure cultures and mixtures of winter wheat and Italian ryegrass, with phosphorus (P) levels recommended by soil testing. The planting proportions of wheat and Italian ryegrass were 100 and 0%, 75 and 25%, 50 and 50%, 25 and 75%, and 0 and 100%, respectively. There was no alleopathic interaction between the species. Both species in all pure and mixed cultures had substantially less growth in the low-P than in the recommended P treatment. However, the relative performance of the two species differed between P treatments. In the recommended P treatment in pure culture, Italian ryegrass had more tillers and greater root weight and length than wheat. Pure culture wheat in the low-P treatment exceeded pure culture Italian ryegrass in leaf area, weights of leaves, stems, and roots, and root length. Thus, the growth of wheat was inhibited less by P deficiency than the growth of Italian ryegrass in pure culture. In the 50:50 mixture of the recommended P treatment, wheat had greater leaf, stem, and root weights than Italian ryegrass. In the 50:50 mixture of the low-P treatment, the two species were very similar in growth, except that Italian ryegrass had about three times more tillers than did wheat. Whereas P deficiency limited the growth of wheat less than Italian ryegrass in pure culture, P deficiency did not affect the relative competitiveness of Italian ryegrass as much as wheat in mixed cultures. The ability of Italian ryegrass to compete with wheat when P was limiting may result from a difference in root growth. Italian ryegrass had a greater fresh root length to fresh root weight ratio than did wheat in the low-P treatment in pure culture and in the 50:50 mixture. The greater surface area of Italian ryegrass roots likely enhanced the competitiveness of Italian ryegrass relative to wheat under P-deficit conditions. Thus, the use of the recommended P nutrition from soil testing may be a key component to diminish Italian ryegrass competition in wheat fields.

Greenhouse experiments in central Texas assessed the relative importance of above- and belowground interactions of semidwarf Mit wheat and Marshall ryegrass during vegetative growth. One experiment used partitions to compare the effect of no (controls), aboveground only, belowground only, and full interaction for 75 d after planting (DAP) one wheat and nine ryegrass plants in soil volumes of 90, 950, and 3,800 ml. The results with the different soil volumes were similar. Wheat growth in the aboveground interaction only did not differ from controls. However, the full or belowground only interaction of wheat with ryegrass reduced wheat height, leaf number, tillering, leaf area, percent total nonstructural carbohydrates in shoot, and dry weights of leaves, stems, and roots 45 and 75 DAP compared to controls. Wheat in full and belowground interaction only did not differ from one another in growth. A replacement series experiment of 56 d also showed that the competitive advantage of ryegrass was relatively greater in root than in shoot growth. No allelopathic response of wheat to ryegrass occurred. While the tallness of the semidwarf wheat minimized aboveground interference by ryegrass, the root growth of the thinner and more fibrous roots of ryegrass greatly enhanced its belowground competitiveness.