Richard L. Vanderlip

Assessing climatic risk to sorghum production in water-limited subtropical environments II. Effects of planting date, soil water at planting, and cultivar phenology

Rainfed crop production in the subtropics is a risky enterprise due to high rainfall variability. When planting opportunities occur, farmers face risky choices because the consequences of decisions made at planting are uncertain. This paper presents a general approach to generating the information required to assistt in making planting decisions in climatically variable subtropical environments. The approach involved coupling a sorghum growth simulation model to long-term sequences of climatic data to provide probabilistic estimates of yield for the range of decision options, such as planting time and cultivar maturity, for a range of soil conditions. The likely change in the amount of stored soil water with delay in planting was also simulated to account for the decision option of waiting for a subsequent planting opportunity. The approach was applied to three locations (Emerald, Dalby and Roma) in subtropical Australia. Production risk varied with location, time of planning, soil water storage, and cultivar phenology. Yield responses to these factors were associated closely with differences in leaf area development and degree of depletion of the water resource. The probabilistic estimates of yield and change in stored soil water provided in this paper can assist decision-makers with risky choices at planting in subtropical environments. Such information can be used in decision analysis or in computerized decision support, where decision-makers, and their risk preferences, can interact directly with the information.

Comparing genetic coefficient estimation methods using the CERES-Maize model

Abstract Many crop simulation models use genetic coefficients to characterize varieties or hybrids. Two methods now used with CERES-Maize to obtain genetic coefficients are: (1) direct experimental measurement; and (2) estimation using the Genetic Coefficient Calculator (GENCALC), an iterative computerized procedure. The objective of this research was to compare an adaptation of the Uniform Covering by Probabilistic Region (UCPR) method with these two approaches. UCPR delineates a joint confidence region for the parameters corresponding to a goodness-of-fit threshold level. The study focuses on two genetic coefficients, duration of the juvenile phase (P1) and photoperiod sensitivity (P2), for five maize hybrids. Field experiments were conducted at Rossville, KS, during 1995 in which genetic coefficients of four of the hybrids were determined. Silking date data for the same hybrids were obtained from the Kansas Corn Performance Tests for use in estimating coefficients with UCPR and GENCALC. UCPR was better than GENCALC at minimizing squared error but at the cost of much longer run times. Both estimation procedures underestimated P1 relative to the field data. This may have resulted from the models propensity to overestimate leaf number. An independent set of silking date data for B73×Mo17 from the Kansas Corn Performance Tests was used for comparing methods. Simulated silking dates using P1 and P2 values obtained by UCPR and GENCALC accounted for only 26 and 47%, respectively, of the variability in actual dates. Both underestimated longer durations to silking. Use of published values for P1 and P2 accounted for 45% of variability but underestimated all data (bias − 9.5 days).

Replanting strategies for grain sorghum under risk

Abstract Risk analysis of replanting strategies for grain sorghum at three Kansas locations was conducted using stochastic dominance techniques. Yield data were simulated for seven planting dates, six seeding rates or target plant populations, and three maturity classes over a 33-year period using weather data for each year at each location. The results showed that optimal planting dates, seeding rates, and maturity classes vary by location and risk preference. In northeast and southcentral Kansas, planting at later rather than earlier dates was preferred as risk aversion increased. In southwest Kansas, generally no change occurred in the preferred strategy as the level of risk aversion increased. Early- and medium-maturing hybrids and low-to-moderate seeding rates often were selected. Late-maturing hybrids never were selected by risk-averse managers. The degree of risk aversion did not significantly affect the selection of a replanting strategy for southcentral and southwest Kansas, but did for northeast Kansas. However, whether managers replanted immediately or delayed, replanting varied with the replanting decision date and degree of risk aversion. Replanting on the first replanting decision date in southwest Kansas rather than delaying 2 weeks or more was preferred by all risk-averse managers. More strongly risk-averse managers in the northeast and all risk-averse producers in southcentral Kansas preferred to delay replanting of damaged stands, in some cases by 2–4 weeks after the decision date. Results also showed that when a stand was damaged late in the season, the expected yield from the damaged stand had to be lower than that from a stand damaged early in the season in order for replanting to occur. Price changes had only minor impacts on the preferred replanting strategies. A higher crop price caused replanting to occur more often, because the yield reduction of a damaged stand required for replanting to be economically feasible grew smaller as the price increased.

Response of pearl millet to grain sorghum environments

Abstract Increasing awareness of drought tolerance in pearl millet [ Pennisetum americanum (L.) Leeke.] has stimulated research into pearl millet as a potential U.S. crop. Objectives of this study were to compare yield and yield components of pearl millet and grain sorghum [ Sorghum bicolor (L.) Moench] and evaluate pearl millet response to a range of grain sorghum environments. Yield and yield component comparisons were made using 24 millet hybrids and six grain sorghum hybrids at seven Kansas locations, from 1980 to 1982. To compare pearl millet production in grain sorghum environments, millet hybrid mean yields were regressed on sorghum location means. A desirable millet hybrid would have a high yield and a regression coefficient not significantly different from 1.0. Average grain sorghum yields were greater than millet yields in all three years. Millet hybrid yields ranged from 350 to 5400 kg ha −1 . Over all locations and years, millet yield averaged 63% of sorghum yield. In unfavorable environments, pearl millet yield and response to changing environments were not significantly different from those of grain sorghum. As environmental conditions improved, sorghum significantly yielded more than millet. Lower millet yields could be attributed to significantly smaller seed size and head sterility. The small seed also reduced plant establishment; however millets tillering ability compensated for reduced population.

Emergence and stand establishment of pearl millet as affected by mesocotyl elongation and other seed and seedling traits

Pearl millet [Pennisetum glaucum (L.) R. Br.] often is grown in semiarid areas where deep planting could provide adequate moisture during early seedling growth. This study was undertaken to determine whether there are genotypic differences in mesocotyl, coleoptyle, and/or primary root development of pearl millet and, if so, whether such differences are associated with variation in ability to emerge and establish from various field and greenhouse planting depths. Seeds of 25 genotypes (17 dwarf and 8 tall) were evaluated in the laboratory for germination and for radicle, mesocotyl, and coleoptile elongation. Seeds of the same genotypes were planted in the greenhouse at 40-, 80-, and 120-mm depths and various depths in the field in 1984 and 1985, then evaluated for emergence and establishment. Among-dwarf and among-tall genotypic differences (P < 0.05) occurred in mesocotyl length, germination percent, and a germination index emphasizing early germination. Dwarf genotypes also differed in radicle and coleoptile length. Dwarf entries significantly exceeded tall in radicle length (25.8 vs. 21.9 mm). Tall genotypes exceeded dwarf in greenhouse emergence and establishment only at the 120-mm depth, even though dwarf and tall entries did not differ in mesocotyl length in the laboratory. Significant field effects occurred mainly in 1985, when dwarf genotypes exceeded tall in establishment at an 80-mm depth (32 vs. 25%, P < 0.05) but not at 40 mm. This dwarf genotype advantage was due to superior post-emergence seedling survival rather than to superior emergence. Results indicate that radicle, mesocotyl, and coleoptile length are of limited value as criteria of field-establishment capability under conventional seeding conditions. Radicle and mesocotyl length appear to have potential as indicators of ability to emerge from greater-than-normal planting depth.

Assessing planting opportunities in semiarid subtropical environments

High rainfall variability in the subtropics makes rainfed crop production a risky enterprise. Planting opportunities are limited by the amount and timing of rainfall. Farmers face a decision of whether or not to plant when an opportunity occurs. This decision depends on the likely yield from different crops and cultivars, the probability of obtaining another planting opportunity, and the yield expectation from that later planting. In this paper, long-term climatic data for six locations in subtropical Australia were used to (i) compare criteria for identifying planting opportunities; and (ii) determine the frequency of occurrence of planting opportunities and the duration between opportunities. Although the occurrence of planting opportunities varied among months and locations depending on the criterion used, very few planting opportunities occur in these environments and the duration between opportunities is relatively long. The mean number of planting opportunities was never greater than one for any month at any location, and frequently (30-70% of years) no planting opportunities occurred in a given month. The highest probability of another planting opportunity occurring in the 30 days following an opportunity was 60%; in most cases the probability was much less. While the results are specific to the locations analyzed, the approach developed is generally applicable where quantifying the risk of planting opportunities is important to decisionmakers.