J. Cárcova - Academia.edu (original) (raw)

Papers by J. Cárcova

Agronomy Journal, 2000

predominantly under dryland conditions. Crop evapotranspiration during a significant proportion o... more predominantly under dryland conditions. Crop evapotranspiration during a significant proportion of the Long-term cropping in the Rolling Pampa of Argentina may reduce growing cycle depends on stored soil water and on the available soil water for maize (Zea mays L.) production. Grain yield, however, has not decreased possibly because of genetic improvement. capacity of the root system to absorb it (Hall et al., Our objectives were to: (i) evaluate root and shoot growth and its 1992). Severe degradation of soil aggregation reduces relation to crop evapotranspiration (ET a), (ii) analyze interactions infiltration rates (Musto, 1979) and can result in deamong hybrids and length of the cropping period on grain yield and creased available soil water. In soil profiles without its components, and (iii) establish functional relations between grain physical constraints, root systems penetrate rapidly. yield components and their determinant processes. Three hybrids with Their ability to grow into inhospitable layers, however, contrasting production stability coefficients and representing different could limit water absorption (Passioura, 1982). Topsoil eras of maize breeding were grown at three farms in 1994 to 1996 in compaction imposed experimentally affected root growth fields with short (S) and long (L) cropping periods on silty clay loam and distribution resulting in reduced ET a (de Willigen soils (fine, illitic, thermic Typic Argiudolls). Silking took place 5 to and Van Noordwijk, 1987; Tardieu et al., 1992). Our 6 d later in L than in S and a significant (P Ͻ 0.05) reduction (21-36%) of ET a was observed in L vs. S around this stage. Lower root abundance hypothesis is that a long period of continuous cropping (reduction of 60%) and canopy size (reduction of 6-13%) in L have in soils with similar genesis results in changes in water probably contributed to less ET a. In addition, the ontogenic delay availability for maize crops. exposed crops grown in L to more stressful meteorological conditions Maize grain yield is mainly related to KN (Bolañ os around silking. Kernel number (KN), closely related to grain yield

Field Crops Research, 1998

Maize production in Argentina is obtained mostly under dryland conditions and grain yield is high... more Maize production in Argentina is obtained mostly under dryland conditions and grain yield is highly related to water availability around silking. Drought, and differences in soil quality caused by intensive land use, sometimes limit water availability for the crop. Field experiments were performed on silty clay loam soils in the temperate humid region of Argentina (32 ° to 35°S, 58 ° to 62°W), to (i) validate a methodology to determine maize water stress (Crop water stress index, CWSI), (ii) describe the behavior of CWSI along the crop cycle of three maize hybrids growing in environments with different soil quality, and (iii) establish the effect of soil quality and hybrids on the relationship between CWSI and available soil water. The CWSI methodology was satisfactorily validated. Crop water stress increased along the growing season in all environments and hybrids. No interactions between soil quality and hybrid on CWSI were found. The effect of soil quality on CWSI did not present a single and clear trend. Differences between hybrids in CWSI were detected. A relationship between CWSI and available soil water was fitted for all hybrids and environments (r 2 = 0.52, n = 51, P < 0.001). The threshold below which crops presented symptoms of water stress was 60% of available soil water.

Field Crops Research, 2008

Maize (Zea mays L.) grain yield is strongly related to the number of harvested kernels, where ker... more Maize (Zea mays L.) grain yield is strongly related to the number of harvested kernels, where kernel number can be increased by synchronously pollinating silks rather than allowing them to be progressively pollinated as they naturally appear from the husks. However, there is scarce evidence on how this practice affects kernel weight (KW) and plant grain yield (PGY), and no report exists on its effects when combined with treatments aimed to reduce apical dominance, like male sterility and detasseling. Field experiments were conducted in two growing seasons (Exp 1 and Exp 2) using two hybrids, cropped at contrasting stand densities (3 and 9 plants per m 2) and including (i) male-fertile and male-sterile versions, (ii) tasseled and detasseled plants, and (iii) natural (NP) and synchronous pollination (SP; pollen added manually to ears bagged 5 days after initial silking) systems. Tassel growth of sterile and fertile versions was also evaluated in a separate experiment (Exp 3). Detasseling increased the number of ears per plant reaching silking (P < 0.001) of NP plants, but this beneficial effect of reduced apical dominance did not improve kernel number per plant (KNP) or PGY. Similarly, the early arrest of anther growth in male-sterile plants had no clear benefit on KNP. In contrast, KNP was enhanced by synchronous pollination (range between À13% and +71%; average of +15.4% in Exp 1 and +3.9% in Exp 2). However, this pollination system promoted a decreased in KW (range between À30% and +4%; average of À11.8% in Exp 1 and À7.8 in Exp 2) such that the treatment had no effect on PGY (range between À19% and +37%; average of +1% in Exp 1 and À4% in Exp 2). Because plant growth rate around flowering was not different between pollination treatments, assimilate availability per kernel was reduced from ovary fertilization onwards in synchronously pollinated plants when compared to open pollinated plants. This explains the reduced KW when increasing KNP by synchronous pollination. In summary, none of the imposed treatments allowed grain yield to be increased at the plant level.

Crop Science, 2001

to be the only factor controlling kernel set when water and nutrients are not limiting growth (Cá... more to be the only factor controlling kernel set when water and nutrients are not limiting growth (Cá rcova et al., Maize (Zea mays L.) kernel set can be improved through synchro-2000). It is well known that kernel set in the subapical nous pollination within and between ears. Reductions in kernel set could be expected because of asynchronous pollination between early-ear depends on synchronous silking and pollination of and late-appearing silks. We analyzed the effect of (i) selective ear both ear shoots (Harris et al., 1976; Motto and Moll, heating around the time of silking, and (ii) different time gaps between 1983; Sarquís et al., 1998). Considering pollination synearly-and late-pollinated silks in an attempt to modify kernel set. chrony within the ear, a significant reduction in kernel Tip ear heating was expected to minimize the advantage of early set has been observed when the pollination interval silking ovaries. Lateral heating and pollination gaps were expected between early-and late-appearing silks in the apical ear to exaggerate this advantage. Three pollination gaps (2, 4, and 6 was artificially increased (Freier et al., 1984). On the d) were tested for two plant populations (3 and 9 plants m Ϫ2). Ear other hand, maize kernel set can be improved signifitemperature in the heated zone averaged 4.5؇C above air temperature. cantly (8-31%) through synchronous pollination, both Temperature in the nonheated side closely followed air temperature. Treatments promoted greater differences in maize kernel number between ears at low plant population and within the (KN) per ear (73% variation) than in the number of silks exposed 5 apical ear at high stand densities (Sarquís et al., 1998; d after silking (6% variation). Lateral ear heating reduced KN per Cá rcova et al., 2000). Apparently, delayed fertilization ear in comparison with the nonheated control, but tip ear heating did of early-silking ovaries allowed some of the late-silking not modify KN per ear. At 9 plants m Ϫ2 , synchronous pollination ones to compensate for their ontogenic delay and set resulted in ෂ15% increase in KN per plant. Pollination gaps of 2 and kernels (Struik and Makonnen, 1992). All these studies 4 d reduced KN per plant drastically (up to 51%), but the reduction suggest that the rate of silk emergence and pollination was smaller for the 6-d gap. This study (i) gives evidence of the timing may explain part of the genotypic differences negative impact of delayed pollination timing among silks on kernel observed in final KN. set, which was not related to reduced silk receptivity, and (ii) defines the time gap for maximum interference of early-on late-pollinated There is little information about the consequences of ovaries, a period shorter than 4 d. altering the natural synchrony of silk emergence and pollination within the apical ear (Freier et al., 1984). Floret development along the ear follows an acropetal pattern of differentiation. Synchrony in floret develop

Crop Science, 2000

interval between anthesis and silking, or between pollination of individual florets. In maize (Ze... more interval between anthesis and silking, or between pollination of individual florets. In maize (Zea mays L.), the later-fertilized ovaries often abort, Research on KN determination in maize has demonthereby reducing kernel set. We examined whether altering the time strated that kernel abortion can be partially overcome interval between pollination of florets within an ear or between ears could affect final kernel number per plant. Synchrony of pollination by increasing assimilate supply of plants under water was varied by natural-and hand-pollination of four hybrids, constress (Boyle et al., 1991; Schussler and Westgate, 1995; trasting in prolificacy (ears plant Ϫ1). Plants were grown in the field Zinselmeier et al., 1995) or low-light stress (Schussler at low (2.5 and 3 plants m Ϫ2) and high (7.5 and 9 plants m Ϫ2) plant and Westgate, 1991; Otegui, 1997). Nevertheless, these populations, without water or nutrient stress. Increasing plant populastudies did not exclude possible interactions with other tion generally delayed silk appearance, but most silks were exposed mechanisms controlling kernel formation (Boyle et al., within 5 d after silking (DAS). Synchronous pollination of all exposed 1991, Zinselmeier et al., 1995). Little knowledge exists, silks on apical and sub-apical ears 5 DAS improved kernel number for example, on hormone-mediated dominance signals (KN) per plant and the floret fertility index (FFI ϭ number of kernels/ (Bangerth, 1989; Dietrich et al., 1995) or the effect of number of pollinated silks), relative to open-pollinated plants. At low pollination rate within and between ears (i.e., number plant populations, the KN plant Ϫ1 increase resulted primarily from a large increase (39-535%, depending upon the hybrid) in kernels on of silks that are pollinated simultaneously) on KN detersub-apical ears. At high plant populations, only apical ears set kernels. mination. In an early study, Freier et al. (1984) reported Synchronous pollination increased KN in these ears 8 to 31%, dea significant reduction in kernel set in apical ear posipending on the hybrid. Thus, timing of pollination had a large impact tions when the pollination interval between early-and on kernel set, and the disadvantage associated with an ontogenetic late-appearing silks on the ear was lengthened artifidelay in silk emergence could be partially overcome by synchronous cially. Pollination of approximately 50% of fertile florets pollination. Because delayed pollination of early-silking ovaries alon the first day silks emerged effectively eliminated lowed a greater number of the late-silking ones to set kernels, factors kernel set on the remaining florets pollinated 7 d later other than assimilate availability per fertile floret likely are involved (Freier et al., 1984). in controlling kernel set.

Crop Science, 2007

Recently, relevant changes have made organizational boundaries more fluid and dynamic in response... more Recently, relevant changes have made organizational boundaries more fluid and dynamic in response to the rapid pace of knowledge diffusion, and innovation and international competition. This helps to reconsider how to succeed with the information and innovation. Information Technology (IT) is increasingly being implemented for strategic reasons, so as to enable improved efficiency and to improve the control and productivity of internal processes. In this perspective, this study aims to identify which management practices projects described in the literature, can be considered as best practices in managing IT projects in the Brazilian context. The literature review enabled the identification of management practices for IT projects and the survey with professional judgment matrix applied to the Brazilian context allowed us to identify, among these, the best practices in the light of the Brazilian experience.

SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.

Crop Science, 2003

In maize (Zea mays L.), the gradient in floret development and silk length along the ear at silki... more In maize (Zea mays L.), the gradient in floret development and silk length along the ear at silking determines a time lag between early- and late-appearing silks, which results in pollination asynchrony between them. This asynchrony is partially responsible of reduced kernel set at the ear tip, and hybrids differ in this trait. The objective of this work was to analyze the pattern of floret and silk differentiation and elongation at different spikelet positions (S n ) along the apical ear of two hybrids of contrasting ear size (DEA ≅ 500 spikelets ear -1 ; DK696 ≅ 800 spikelets ear -1 ). At silking, both hybrids had reached approximately the same proportion of final ear length (about 44%), but DK696 had differentiated a greater number of spikelets row -1 (46 spikelets) than DEA (33 spikelets). Silk initiation rate was always faster than spikelet initiation rate, and silk extension dynamics was similar for all spikelet positions. Silks from the base of the ear were always longer than those from the tip (S 25 in DEA or S 35 in DK696). Before pollination, silks experienced an early phase of exponential elongation followed by a phase of linear growth. A drastic reduction in elongation rate followed silk emergence, which did not occur when ears were bagged and pollination was prevented. Convergence in silking among spikelets along the ear could be attained by (i) synchronous silk initiation among spikelet positions, followed by a similar pattetn of silk elongation in all florets (hybrid DEA), or (ii) increased silk elongation rate in apical florets (hybrid DK696).