John M. Nelson

Planting date and nitrogen fertilization effects on lesquerella production

Abstract Lesquerella (Lesquerella fendleri (Gray) Wats.) produces seed containing hydroxy fatty acids similar to castor oil and has good commercial potential. An important step in the commercialization of this plant for the southwestern desert regions of the United States is the development of an efficient agronomic production system. Field experiments were conducted during the 1991–1992, 1992–1993, and 1993–1994 growing seasons at the University of Arizona, Maricopa Agricultural Center, Maricopa, Arizona to determine the effect of planting date and nitrogen fertility on lesquerella seed yield. Results indicate that fall plantings are necessary to obtain high seed production. September plantings generally produced higher yields than the October or November plantings. February plantings produced low yields and appear to be too late for a growing season that ends in June in central Arizona. In all years, lesquerella responded to nitrogen (N) fertilizer. The addition of 60 to 120 kg N/ha increased biomass and seed yields. Nitrogen fertilizer did not affect 1000-seed weight, but decreased seed oil content in the 1993–1994 planting. There is evidence that increasing the N application rate decreases seed oil content in lesquerella.

Nitrogen fertilization effects on lesquerella production

Abstract Progress has been made towards the commercialization of Lesquerella fendleri (Gray) Wats. as a fall-planted oilseed crop for the southwestern United States. Research to develop suitable cultural practices for commercial production of lesquerella has been underway since the late 1980s; however, information is limited on the plant’s nitrogen (N) requirement. Field experiments were conducted during two growing seasons to determine the optimum amount and timing of N applications for lesquerella production. Yield results indicate that lesquerella grown on desert soils is strongly influenced by N fertilization. Nitrogen rates as high as 180 kg N ha−1 increased seed yield. Seed oil content decreased as the N rate was increased. The increase in seed yield at the higher N rates generally offsets the decrease in oil content, but oil yields appeared to be near maximum at 180 kg N ha−1. Split-applications of N in the Spring increased seed and oil yields in one of two seasons. Nitrogen had no influence on 1000-seed weight or lesquerolic acid content of the oil. No Spring leaf blade total N level was identified as being related to maximum seed yield. A suggested N management program for lesquerella production is to apply a small portion of N at planting time and the major portion of N in several applications during the period from onset of bloom through full bloom (February–April).

Irrigation effects on pinitol content of jojoba leaf blades and floral buds

Abstract One of the factors limiting jojoba (Simmondsia chinensis (Link) Schneid.) production in the USA has been frost damage to flower buds. Research indicates that drought can be used to increase the frost tolerance of jojoba. In certain other plants, frost-hardiness is related to an increase in soluble carbohydrates including pinitol. D-Pinitol is also present in jojoba and is a major soluble sugar constituent of its leaves and buds in the fall and winter. In this study we evaluated the influence of irrigation water management, season and clone on pinitol content of jojoba over a 2 year period. The plants studied were from two clones in two irrigation regimes: a wet treatment (WT) that received water biweekly throughout the growing season, and a dry treatment (DT) that received no irrigation water after June to provide fall and winter water stress. Leaf water potential and relative water content were lower in the fall and winter in the DT than in the WT. Water stress did not appear to stimulate pinitol accumulation in jojoba leaves or flower buds. Pinitol content of leaves was highest in the spring and lowest in the summer. There were no consistent differences between clones in pinitol content of tissue.

Flowering and seed yield of lesquerella as affected by nitrogen fertilization and seeding rate

The lesquerolic acid in lesquerella seed can be used in industrial applications such as greases, cosmetics, polishes, inks, and coatings. Successful commercialization of lesquerella will depend on the development of improved cultural practices. Lesquerella flowers are bright yellow and are prominently displayed. As a result, many cultural practices could be tied to flowering in a qualitative way. A new method of estimating flowers such as those of lesquerella using digital images has been developed that is rapid, not labor intensive, and can be automated. The purpose of this study was to determine the effects of nitrogen fertilizer and plant density on flowering of lesquerella and to develop relationships between seed yield and flowering. The lesquerella crop was planted on 15 October 1997, at the Maricopa Agricultural Center, approximately 40 km south of Phoenix, Arizona on a variable Mohall sandy loam (fine-loamy, mixed hyperthermic, Typic Haplargid). The experimental design was a complete factorial of three fertilizer rates and four seeding rates. Ammonium sulfate at rates of 0, 60 and 120 kg of N ha−1 was applied at flowering on 18 March 1998. Digital images of the plots were taken periodically from 19 March 1998 to 4 June 1998 using a color digital camera. Images were acquired between 1030 and 1300 h MST. In this experiment, the crop did not respond to seeding rate. Flowers present at initial bloom could be used to estimate stand establishment. The early flowers did not contribute much to final yield, but flowers present in the first 3 weeks of May were a good predictor of yield. Flowering increased with N additions and noticeable peaks in flowering occurred after irrigations. The new method was verified as a viable method for estimating flower number. The method of flower estimation should also be useful for plant breeders for selection of earlier maturing lines, which would increase the potential for use of lesquerella in rotational systems.

Nitrogen fertilization effects on jojoba seed production

Abstract Although jojoba (Simmondsia chinensis (Link) C. Schneider) has been cultivated in the United States for many years, information is limited on the plants nitrogen (N) requirement. A 10-year field study, which began with 2-year-old plants, evaluated the effect of N application rates on growth, flower bud survival, seed yield, seed weight, seed wax content and leaf blade total N content of three clones. Nitrogen rates were 0, 30 and 60 kg N per ha per year for the first 4 years and then were increased to 0, 60 and 120 kg N per ha per year for the remaining 6 years of the study. Nitrogen rates had a significant effect on growth in height in only 1 year. Growth was generally less in years when high seed yields were produced. Seed yields were increased linearly by N rate in 4 of the 7 years that crops were produced. Nitrogen rate had no effect on flower bud survival. Highest bud survival followed winters with temperatures no lower than −3°C and little or no survival occurred when temperatures reached −6 or −7°C. Seed weight was increased by N in 3 of the 7 years. A negative linear relationship existed between seed yield and seed weight. In 5 of the 7 years, seed wax content was reduced as the N rate was increased. Seed yields of clones varied among years, but AT-1310 had the highest seed wax content in 4 of the 7 years. Leaf blade total N content generally increased linearly as the N rate was increased after the first 3 years of the study. Based on leaf N content and seed yields obtained over a 7-year period, it appears that a leaf N content lower than 2% from July through September is associated with reduced seed yield in the following crop year.

Phenotypic variation of agronomic traits among coyote gourd accessions and their progeny

As a prelude to domestication efforts, variation of agronomic traits was determined among accessions of the polytypic, xerophytic cucurbit, coyote gourd [Cucurbita digitata subsp. digitata (DIG), palmata (PAL), cylindrata (CYL), and cordata (COR)] and among and within their progeny. Oil content in 60 accession seed lots (x = 27.8%, CV 21.4%) was more variable than protein content (x = 33.1%, CV = 13.5%). Punicic acid (c,t,c-9,ll,13-octadecatrienoic acid) levels in seed oils were also variable (x = 12.0%, CV = 20.6%) among accession seed lots. Substantial differences among and within subspecies were noted in 40 progeny lines for fruit/plant (x = 55.2, CV = 47.5%), seed wt/plant (x = 0.89 kg, CV = 51.1%), seed wt/fruit (x = 17.4 g, CV = 39.8%), seed no./fruit (x = 356, CV= 30.8%), 100-seed wt (x = 4.8 g, CV = 21.6%) and fruit diameter (x = 77 mm, CV 4.8%). Correlations among parameters suggested selection for fruit/plant to be the most effective primary strategy for seed yield improvement, but among high fruit-yielders, selection for seed wt/fruit was also important. The two subspecies PAL and CYL exhibited superior seed wts/plant. CYL types matured high fruit-loads, but their fruits were smaller and contained a smaller number of lighter seed than PAL or PAL hybrids. In contrast, PAL and PAL hybrids displayed lower fruit-yields/ plant but their fruits were larger and contained higher seed wts/fruit than their CYL counterparts. Root wt/plant was also variable (x = 1.55 kg, CV = 63.2%). Roots of DIG were larger and less branched than those of other subspecies. Proximate and liquid Chromatographic analyses of selected accession seed lots and controlled crosses failed to reveal advantages for the inclusion of specific types in a breeding program for the development of high oil or high/low punicic acid lines.RésuméComo un preludio a los esfuerzos de domesticación, se determinó la variatión de caracteres agronómicos entre ejemplares delpolitipo de cucurbitas xerofitas, “calabacillas coyote ” [Cucurbita digitata subspp. digitata (DIG), palmata (PAL), cylindrata (CYL), y cordata (COR)] asi como en y entre su progenie. El contenido de aceite en 60 lotes de semillas de los ejemplares (x = 27.8%, CV = 21.4%) fué más variable que el contenido protéico (x = 33.1%, CV = 13.5%). Los nivelés de ácido punícico (c,t,c-9,11,13-ácido octadecatrienóico) en los aceites de las semillas fureon también muy diversos y variables (x = 12%, CV = 20.6%), entre los lotes de semillas de la colección. Se apreciaron diferencias substantiates entre y dentro de las subespecies en las 40 líneas de progenie para la relatión fruto/planta (x = 55.2, CV = 47.5%), peso de semilla/planta (x = 0.89 kg, CV= 51.1%), peso de semilla/fruto (x = 17.4 g, CV=21.6%), numúro de semillas/ fruto (x = 356, CV = 30.8%), peso de 100 semillas (x = 4.8 g, CV = 21.6%) y diámetro defruto (x = 77 mm, CV = 4.8%). Las correlaciones entre los parâmetros sugieren que seleccionar por la relatión fruto/planta, seíria la estrategia primaria más efectiva para fines de mejorameiento en el aspecto de rendimiento de semilla, pero entre los productores de fruta, seleccionar por la relatión peso de semilla/fruto, es también importante. Las dos subespecies, PAL y CYL mostraron una relatión peso de semilla/planta superior. Los tipos CYL maduraron altos lotes de fruto, pero losfrutos eran mas pequeños y contenían un menor número de semilla liviana que aquellos del tipo PAL o sus híbridos. En contraste, PAL y sus híbridos tuvieron menores rendimientos de fruta/planta pero los frutos fueron mas grandes y con una relatión peso de semilla/fruto mayor que en el caso de CYL. El peso radicular/planta también varió (x = 1.55 kg, CV = 63.2%). Las raices de DIG fueron mayores y menos ramificadas que aquellas de otras subespecies. Los análisis proximales y de cromatografía líquida de lotes específicos de semillas de la colección no revelaron ninguna ventaja para la inclusión de tipos específicos en un programa de mejoramiento para el desarrollo de líneas con alto contenido de aciete o alto/bajo ácido punícico.

Hesperaloe water requirement and management for biomass production

Abstract Hesperaloe (Hesperaloe funifera (Koch) Trel.) has potential as a new source of fibers for specialty papers. Agronomic research on Hesperaloe has been in progress since the 1980s, however, limited information is available on its water use requirement and yield response to irrigation. A study to assess the influence of water management on leaf yield and seasonal water use of Hesperaloe grown as a perennial crop was conducted during 1995–1999 in a flood-irrigated planting established from transplants in November 1994. Irrigation treatments evaluated were: (T1) irrigate when available soil water was 25–35% depleted in the top 0.6 cm of soil; (T2) irrigate at 40–50% depletion; (T3) irrigate at 50–60% depletion; and (T4) irrigate at 70–80% depletion. Treatments T1 and T2 resulted in the highest leaf yields, 93–94 Mg/ha fresh leaf weight, at the end of 5 years. Comparable yields for T3 and T4 were T1=77 and T2=46 Mg/ha. In 1999, the fifth year of production, T1 and T2 produced leaf yields of 34–36 Mg/ha. Average evapotranspiration (ET) for 1996–1999 was 753 mm/year for T1 and 676 mm/year for T2. Total ET in 1999 for T1–T4 was T1=830, T2=786, T3=727 and T4=517 mm. The peak ET rate was 4.34 mm/day and occurred in T1 during July 1999. Hesperaloe was observed to have a shallow, horizontal root system. The highest water use efficiency (WUE) achieved was 1.49 kg leaf dry weight per m3 of water for T2 in 1997. Average WUE for T2 for 1996–1999 was 1.10 kg leaf dry weight per m3 of water. In this study, managing water to maintain available soil water at 40–50% depletion resulted in maximum leaf yield and high WUE.