James J. Heitholt

Nitrogen partitioning in genotypes of winter wheat differing in grain N concentration

Abstract A three-year field study was conducted to establish the relationship between grain yield, grain N concentration ( gnc ), post-anthesis N uptake, and nitrogen harvest index in winter wheat ( Triticum aestivum L.) genotypes varying in gnc . Yield was negatively associated with gnc but correlation between the two was only moderate (−0.43 to −0.60 ∗ ). Genotypes differed in flag leaf nitrate reductase activities ( nra ), but nra was not correlated with gnc , total grain N, or yield. Nitrogen harvest index, which ranged from 0.55 to 0.78, was not correlated with gnc or yield. Redistribution of vegetative N contributed significantly more to grain N than post-anthesis N uptake, which generally accounted for less than 10% of the total N at maturity. The range of post-anthesis N-uptake values among genotypes was also small and not significantly different between genotypes. Vegetative N at maturity increased as a result of supplemental N applied at anthesis, but gnc , total grain N, and yield were unaffected. Apparently, the additional N was not easily partitioned to the grain. Since nitrogen harvest index and other N-redistribution variables were not correlated with gnc , improvement in gnc may require an improvement in both post-anthesis N uptake and increased partitioning of that N to the grain.

COPPER, MANGANESE, AND ZINC FERTILIZATION EFFECTS ON GROWTH OF SOYBEAN ON A CALCAREOUS SOIL

ABSTRACT High pH may limit micronutrient availability for soybean (Glycine max L. Merr.) on Blackland soils found in northeast Texas. However, it is not clear whether preplant additions of micronutrients will enhance soybean growth or yield on this soil. In three separate greenhouse studies, a pH 8.3 Houston Black clay (fine, smectitic, thermic Udic Haplusterts), with DTPA-extractable concentrations of 0.74 mg copper (Cu) kg−1, 3.74 mg manganese (Mn) kg−1, and 0.47 mg zinc (Zn) kg−1, was treated with CuSO4 (0, 25, 50, 75, and 100 ppm Cu), MnSO4 (0, 10, 20, 30, and 40 ppm Mn), or ZnSO4 (0, 2, 4, 6, and 8 ppm Zn). Pot size was 19 L and soil dry mass was 10 kg. Soybean (cv. Hutcheson) seed were planted in either February or April 2000 and seedlings were thinned to three per pot at the first true leaf stage. One leaf from each plant was harvested at growth stage R3 for nutrient analysis. Between 20 and 110 days after planting, five to six nondestructive leaf chlorophyll readings were obtained. Plants were destructively harvested at R6 (mid podfill) for nutrient and yield determination. No visible symptoms appeared through early reproductive growth, but by growth stage R5 (beginning seed), leaves from the 0 ppm Cu treatment were chlorotic. Chlorophyll (SPAD 502) values of the 3rd uppermost leaf during the R3 to R5 growth stages were greater when Cu, Mn, and Zn were added to the soil than in the 0 ppm treatment. Fruit yield (seed plus pod walls) at growth stage R6 was greater in pots receiving 25 to 100 ppm Cu, 20 to 40 ppm Mn, and 4 to 8 ppm Zn than in the check treatment. Total biomass was increased by 25 to 100 ppm Cu, but there was only a trend for Mn or Zn to increase biomass. Because fruit yield increases were observed as a result of an addition of the micronutrients applied individually, a combination of micronutrients may increase yield further. There was no evidence that the higher rates of Cu, Mn, or Zn caused reduced growth. In summary, these greenhouse results indicated that field studies testing the effects of Cu, Mn, and Zn on soybean yield on this calcareous soil are warranted.

Soybean Growth on Calcareous Soil as Affected by Three Iron Sources

Abstract Iron (Fe) chlorosis is a common symptom in many soybean (Glycine max L. Merr.) producing areas throughout the United States. On the Blackland soils found in northeast Texas, Fe chlorosis occasionally appears during vegetative growth, but often abates by the time plants flower. However, it is not clear whether preplant additions of Fe will enhance soybean growth or yield on this soil or whether different sources of Fe give different responses. In a greenhouse study, soil from a pH 8.4 Houston Black clay (fine, smectitic, thermic Udic Haplusterts), with a DTPA‐extractable concentration of 11.7 mg Fe kg−1, was treated with FeSO4 (0, 3, 10, 30, and 100 ppm Fe), sodium ferric diethylenetriamine pentaacetate (FeDTPA) (0, 0.3, 1.0, 3, and 10 ppm Fe) or sodium ferric ethylenediamine‐di (o‐hydroxyphenylacetate) (FeEDDHA) (0, 0.3, 1.0, 3, and 10 ppm Fe). Pot size was 19 L and soil dry mass was 10 kg. Soybean (cv. Hutcheson) seed were planted in November 2000 and seedlings were thinned to three per pot at the first true leaf stage. The third uppermost fully expanded leaf of each plant was harvested at growth stage R3 for nutrient analysis. Between 20 and 100 days after planting, six nondestructive leaf chlorophyll readings were obtained from the third uppermost fully expanded leaf. Entire plants were harvested at R6 (mid podfill) for nutrient and biomass yield determination. Leaf blade Fe concentration ranged from 79 to 87 mg kg−1 in the untreated check plants to a high of 109 mg kg−1 for the 10 ppm FeDTPA‐Fe treatment, all of which were greater than the acknowledged critical level of 60 mg kg−1. No visible Fe‐deficiency symptoms appeared during the study. Chlorophyll (SPAD 502) values during the R3 to R5 growth stages were greater for all of the FeSO4 treatments than for the 0 ppm treatment. The 10 ppm FeDTPA‐Fe treatment and the 3 ppm FeEDDHA‐Fe treatment exhibited higher leaf chlorophyll readings than the untreated checks during the R3 to R5 growth stage. The average seed yield from the 12 Fe fertilized treatments at growth stage R6 was only 12% greater (not significant) than the untreated check. Total biomass (root plus shoot) was not affected by the treatments. There was no evidence that the higher rates of Fe caused reduced growth. Overall, our results do not suggest that soil‐applied Fe will consistently stimulate soybean growth or yield on this soil, at least when DTPA‐extractable soil Fe is at 12 mg kg−1 or higher. However, because of the trends for increased seed yield in some of the Fe treatments, field studies using soil‐ and/or foliar‐applied Fe are warranted.

Effects of foliar urea‐ and triazone‐nitrogen, with and without boron, on cotton

Abstract Optimal lint yield in recently released high‐yielding upland cotton (Gossypium hirsutum L.) cultivars requires careful nutrient management. It is not known whether these cultivars are capable of responding to foliar nitrogen (N) and boron (B) fertilizer when conventional soil fertility practices are used. The objectives of this study were (i) to determine the responses of a high‐yielding cotton cultivar to foliar N and B fertilizer and (ii) to compare two N sources when applied to foliage of cotton. A two‐year field study was conducted with a factorial arrangement of three N treatments and two B treatments. Plants received foliar applications of the surfactant Tween 20 in H2O (check), or one of the following treatments plus surfactant: B (as H3BO3), triazone‐N (24% of N as S‐tetrahydrotriazone), triazone‐N plus B, urea‐N, or urea‐N plus B. Leaf blade mineral element composition, lint yield, and fiber properties were determined. Averaged across years, lint yields were significantly higher in the c...

Cotton: Factors Associated with Assimilation Capacity, Flower Production, Boll Set, and Yield

Nearly all cotton yield physiology research has been conducted on either Gossypium hirsutum (upland cotton) or G. barbadense (Pima or extra-long staple cotton) since these two species represent more than 90% of the world’s cultivated cotton crop. Therefore, this chapter will primarily review the literature dealing with upland and Pima cotton genotypes. The history of introductions that led to upland and Pima cottons was described by Meredith (1991). The role of genetics in improving yield and fiber quality of cotton were presented in reviews by Meredith (1984a, 1991) and Culp (1994).

Forage from Soybean Provides an Alternative to Its Poor Grain Yield in the Southern Great Plains

The economic potential for soybean (Glycine max L. Merr.) as forage, compared to its potential as grain, creates a dilemma for soybean farmers in the southern Great Plains. To better understand these two potential uses, soybean cultivars differing in maturity and growth habit were planted in 14-inch and 28-inch rows on 11 May 2001 and 16 May 2002 near Dallas, TX. The soil was a Houston Black Clay (fine, smectitic, thermic Udic Haplusterts). Plant height, plate meter readings, and forage biomass were measured in July and August and grain yield determined in September. Forage (1.26 to 2.13 ton/acre) and grain yields (9.3 to 20.9 bu/acre) were relatively low and similar between row spacings and between cultivars. Forage quality traits ranged as follows (by dry weight): crude protein (8.7 to 17.2%), acid detergent fiber (24.1 to 33.6%) and neutral detergent fiber (33.2 to 48.9%), in vitro dry matter digestibility (69.2 to 78.6%), and relative feed value (120 to 196). Plate meter readings and plant height were each correlated to biomass in one season but not both. Because of its relatively high forage quality and low grain yields, harvesting any of the soybean cultivars for forage during mid-season would have been more profitable than harvesting for grain, given the hay and grain market prices when the experiments were conducted.

Influence of deflowering on dry matter production of soybeans

Abstract Soybeans ( Glycine max (L.) Merr.) of maturity group 00 were grown in a greenhouse to investigate the effect of continuous flower removal on growth and dry matter partitioning. After growth stage R1 (initial bloom) one-half of the plants were deflowered daily for 50 days. Plants were harvested at 10-day intervals, beginning at R1, and continuing until control plants reached maturity. Total dry matter (all vegetative plant parts plus fruits, where present) was similar for both treatments at 30 days after R1; however, the total dry matter of the deflowered plants was greater than the controls at 40 and 50 days after R1. There was no difference in the photosynthetic rate of single leaves for 30 days after R1. Deflowering had only a minimal effect on the leaf area, number of branches, number of branch nodes, and plant height. Thus, the increase in the mass of the vegetative plant parts in the deflowered plants resulted primarily from an increase in specific leaf weight and thicker stems and branches. The relative proportion of the total vegetative weight represented by a given vegetative component was not greatly altered by flower removal. The results suggest that the vegetative plant parts in soybeans can serve as strong sinks for photosynthate when reproductive structures are not allowed to develop.

Toxicity and uptake of nitroguanidine in plants

During the manufacture of the munition nitroguanidine (NQ), wastewater is contaminated by NQ and related by-products. Land application of the NQ-contaminated wastewater was initiated after discussions with the Kansas Department of Health and the Environment and the US Environmental Protection Agency. This treatment method has been a cost-effective and convenient means of disposal. The environmental fate of NQ is related to plant uptake and metabolism as well as metabolism by plant consumers and decomposers. Toxicity of NQ in vertebrates has been found to be very low. Land application of NQ-contaminated wastewater will result in NQ penetration into the root zone where the potential for absorption exists. However, virtually nothing is known of the uptake and metabolism of NQ in plants. The objective of this study was to test the toxicity of and to characterize the uptake of NQ in plants.

Comparison of adjuvant effects on cotton leaf potassium concentration and lint yield 1

Abstract Visual mid‐season potassium (K) deficiencies in cotton (Gossypium hirsutum L.) have recently been reported in many parts of the Cotton Belt. Foliar K sprays are sometimes used to correct these mid‐season deficiencies. However, little is known about the uptake of K by leaves, whether spray adjuvants or surfactants facilitate movement of K into leaves, or whether foliar‐applied K plus adjuvants enhance lint yield. The objective of this study was to compare the efficacy of spray adjuvants when mixed with foliar potassium nitrate (KNO3) solutions. Three field experiments (one K concentration time‐course study and two foliar‐applied K lint yield studies) were conducted. In the time‐course study, plants were sprayed over‐the‐top once during mid‐bloom with a 11.2 kg KNO3/ha (4.3 kg K/ha). Leaf blade and petiole K concentration were monitored at 0, 2, 4, 6, 24, and 48 h after application. The KNO3 solutions were applied alone or with either Tween 20 (a commonly used laboratory surfactant), Kinetic, Dyne‐...

The Influence of Cotton Seed Weight on Fibers Per Seed and Fiber Property Uniformity

ABSTRACT Increasing cotton (Gossypium hirsutum L.) fiber weight per seed in some genotypes has the potential to increase micronaire values to levels that trigger price discounts. Strategies need to be developed that limit cell wall deposition. Seed weight decreases as the number of seeds per boll increases. Characterization of the relationship between seed weight, fibers per seed and fiber properties will supply basic information for strategy development. Stoneville 474 and FiberMax 832 were grown under irrigated conditions in 1998 and 1999. First position flowers were harvested on the day of anthesis for fiber density and perimeter analysis. Remaining first position bolls were harvested after boll opening and bolls were individually analyzed for weight and fiber properties. Initial fiber densities were similar for both cultivars. Mean fiber length and cell wall thickness were positively correlated with final seed weight. Fiber length variability decreased as seed weight increased. The decrease in length variability paralleled an increase in fiber cell wall thickness. Strategies to increase the number of seeds per boll may reduce micronaire values but increase length variability.