Dynamics of soil microbial biomass and nitrogen availability in a flooded rice soil amended with different C and N sources

 A greenhouse experiment was conducted to compare effects of different C and N sources applied to a flooded soil on soil microbial biomass (SMB) C and N, extractable soil organic N (N_ORG), and NH₄ ⁺-N in relation to plant N accumulation of rice (Oryza sativa L.). In addition to a control without inputs (CON), four treatments were imposed receiving: prilled urea (PU), rice straw (RS), RS and PU (RS+PU), or Sesbania rostrata as green manure (SES). Treatments were arranged according to a completely randomized design with four replicates and further consisted of pots with and without transplanted rice. While plant effects on the SMB were relatively small, the application of organic N sources resulted in a rapid increase in SMB until 10 days after transplanting (DAT) followed by a gradual decline until 73 DAT. Plant N accumulation data in these treatments clearly indicated that the SMB underwent a transition from a sink to a source of plant-available soil N during the period of crop growth. Seasonal variation of the SMB was small in treatments without amendment of organic material (CON, PU) presumably due to a lack of available C as energy source. Extractable N_ORG was significantly affected by soil planting status and organic N source amendment, but represented only a small N pool with little temporal variation despite an assumed rapid turnover. Among the three treatments receiving the same amount of N from different sources, the recovery efficiency of applied N was 58% for PU and 28% for both RS+PU and SES treatments at 73 DAT. The N uptake of rice, however, was not driven by N availability alone, as most evident in the RS+PU treatment. We assume that root physiological functions were impeded after application of organic N sources. Received: 1 June 1999     

A comparative study of the anatomy of the omasum in domesticated ruminants

The structure of the omasum was compared in 10 water buffalo (Bubalus bubalis), 10 Shorthorn cattle (Bos indicus), 9 Merino sheep (Ovis aries) and 10 cross-bred goats (Capra hircus), and the functional significance of the differences is discussed. The weight of the omasum and area of the internal laminae appeared to be smaller in Brahman cattle than the buffalo and British cattle. When compared in relation to body weight, the omasums of caprid animals were smaller than those of bovids, by a factor of 0.33-0.67 but the omasums of goats were appreciably larger than sheep. The number of laminae ranged from 33 to 35 for the sheep and goats compared with 122 to 169 for the buffalo and cattle. It is suggested that the marked difference in structure of the omasum between the small and large ruminants may influence the food intake of these animals through the effects of this gut compartment on absorption of nutrients and passage of digesta.     

Estimating maize nutrient uptake requirements

Generic, robust models are needed for estimating crop nutrient uptake requirements. We quantified and modeled grain yield–nutrient uptake relations in maize grown without significant biotic and abiotic stresses. Grain yield and plant nutrient accumulation in above-ground plant dry matter (DM) of commercial maize hybrids were measured at physiological maturity in on-station and on-farm experiments in Nebraska (USA), Indonesia, and Vietnam during 1997–2006. These data were used to model the nutrient requirements for yields up to 20 Mg ha⁻¹ using the QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) approach. The model required estimation of two boundary lines describing the minimum and maximum internal nutrient efficiencies of N, P and K (IE, kg grain per kg nutrient in plant DM), which were estimated at 40 and 83 kg grain kg⁻¹ N, 225 and 726 kg grain kg⁻¹ P and 29 and 125 kg grain kg⁻¹ K, respectively. The model predicted a linear increase in grain yield if nutrients are taken up in balanced amounts of 16.4 kg N, 2.3 kg P and 15.9 kg K per 1000 kg of grain until yield reached about 60–70% of the yield potential. The corresponding IEs were 61 kg grain kg⁻¹ N, 427 kg grain kg⁻¹ P and 63 kg grain kg⁻¹ K. The model predicted a decrease in IEs when yield targets approached the yield potential limit. A spherical model was derived from QUEFTS model outputs and found to be particularly suitable for practical applications such as estimating fertilizer needs. The proposed spherical model offers generality across environments and management practices, allowing users to estimate the optimal N, P and K uptake requirements based on two inputs: estimated yield potential and yield target. Further improvements in modeling the relationship between N uptake and grain yield can be made by taking into account differences in harvest index. Accuracy in the simulation of N uptake using the spherical model was improved from an RMSE of 35 kg N ha⁻¹ to 25 kg N ha⁻¹ when harvest index was accounted for, suggesting that the relationship between N uptake and actual yield is affected by both yield potential and efficiency in biomass partitioning.     

Selection before backcross during exotic germplasm introgression

Introgression of genes from exotic germplasm into breeding populations can broaden the genetic base of crop improvement. Only a very small percentage of genetic variability has been used in crop breeding programs. Traditionally, F₁ plants are used to backcross to the adapted lines or populations. An alternative approach is to backcross the F₂ individuals selected for agronomic acceptability. Our objective was to determine whether selection before backcross would lead to more progenies with both high yield and acceptable levels of agronomic performance than direct backcross without selection. To test the feasibility of the proposed approach, we conducted parallel experiments in which two exotic sorghum accessions were crossed to two adapted sorghum parents and further backcrossing was conducted with either F₁ or selected F₂ plants. Fifty random S₁ families were evaluated in three test environments. Although selection before backcross resulted in a higher frequency of families with maturity equal to or earlier than those of the adapted parents, no consistent changes in grain yield and plant height were observed between populations with and without selection. Similar results were found with either an inbred or a population as the recurrent parents. Given these findings and the extra generation required, we do not recommend selection before backcross in the process of introgression of exotic germplasm.     

Exploring ethyl methanesulfonate (EMS) treated cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) to improve drought tolerance

The Texas High Plains often has extended periods between rainfall events, which can lead to a reduction in the yield and fiber quality of cotton (Gossypium hirsutum L.). It is known that cultivated cotton suffers from low levels of genetic diversity due to the over-use in breeding of similar gene pools, which may hinder breeding for drought tolerance. In this study, for the first time the novel variability or genetic diversity of morphological and agronomic traits possibly created by the chemical mutagen ethyl methanesulfonate (EMS) was evaluated to improve drought tolerance in cotton by traits’ response to different irrigation regimes. EMS is a chemical mutagen that has been shown to cause point mutations in the DNA of many model plants and crop species. Three EMS treated lines were advanced from the M₁ to M₄ generation as bulk-harvested populations. A diverse selection scheme was applied to capture most of the genetic trait-variability or diversity and superior lines in these populations. In 2014–2016 the diversity of these populations was evaluated based on four agronomic and thirteen morphological traits to determine differences in response to multiple irrigation rates. Analyses of these traits showed statistically significant (p?≤?0.05) differences between and within populations when compared to the original non-treated EMS source, with most of the variability being observed in the high irrigation rate. However, none of the EMS treated populations had significantly (p?≤?0.05) better lint yield than the commercial cultivar (control) in 2016. EMS yield performance was possibly constrained by the applied diverse selection scheme of this study. Traits such as total number of bolls, bolls retained at node 7 and below, and those retained between nodes 8 and 12, and bolls retained at node of first fruiting branch may be predictors to improve cotton production (yield) in water limiting environments.     

Identification of lactoferrin and glutamate receptor‐interacting protein 1 in bovine cervical mucus: A putative marker for oestrous detection

Accurate detection of oestrus is important for artificial insemination. The aim of this study was to identify oestrous‐specific bovine cervical mucus proteins that could be used to determine the optimal time for artificial insemination. Non‐oestrous and controlled internal drug release (CIDR)‐induced oestrous‐stage mucus proteins were purified and subjected to surface‐enhanced laser desorption/ionization time‐of‐flight mass spectrometry, sodium dodecyl sulphate polyacrylamide gel electrophoresis and MALDI‐TOF/TOF. Among differentially expressed proteins, lactoferrin (LF) and glutamate receptor‐interacting protein 1 (GRIP1) showed a twofold increase during the CIDR‐induced oestrous stage compared to the levels in non‐oestrous stage in bovine cervical mucus. The RT‐PCR, Western blotting and immunohistochemistry results showed that LF and GRIP1 expression was significantly increased during the oestrous stage in the uterus. This study demonstrated that bovine LF and GRIP1 exist during the oestrous stage, but not during the non‐oestrous stage, suggesting that cervical mucus LF and GRIP1 are useful oestrous detection markers in cattle.     

Factors Affecting the Readiness and Preparation of Replacement Heifers in Tropical Breeding Environments

The future of beef cattle production in tropical regions is uncertain because of land tenure concerns, threatening the survival of extensive management programmes in these areas of the world. The need to intensify production systems will inevitably lead to changes in the management of replacement animals in existing herds. The present review underlines the main constraints, which in the past could be resolved by the sheer numbers of animals present in beef cattle operations, with replacements reliant only on finding enough heifers to substitute the adult females destined for culling. This scenario is rapidly changing as beef cattle units in tropical regions subdivide to share out the land between as many farmers as possible. Consequently, issues such as the efforts needed to manage the pregnant cow, particularly her nutritional status and its effect on the new‐born calf, the future replacement heifer growing in the presence of the dam, weaning management and procedures required before a heifer can be introduced into a breeding programme, need to be adequately and efficiently addressed by farmers in tropical regions.     

Influence of Cysteamine on In Vitro Maturation, In Vitro and In Vivo Fertilization of Equine Oocytes

The effect of cysteamine on in vitro nuclear and cytoplasmic maturation of equine oocytes collected by transvaginal ultrasound guided follicular aspiration was assessed. Oocytes were matured in vitro with (cysteamine group) or without (control group) cysteamine. The nuclear stage after DNA Hoechst staining, penetration rates after two different in vitro fertilization (IVF) techniques (IVF media with ionophore and Hepes buffer with heparin) and the embryo yield following oocyte intra-oviductal transfer were used as a criterion for assessing nuclear and cytoplasmic maturation, respectively. Contrary to the data described in other domestic species, there was no effect of cysteamine on in vitro nuclear maturation, IVF or in vivo embryonic development under our conditions. Ovum pick up yields (52%) and maturation rates (control group: 47% and cysteamine group: 55%) were similar to those previously reported. From 57 oocytes transferred to the oviduct in each group, the number of embryos collected was 10 (17%) in the control group and five in the cysteamine group (9%). Those two percentages were not statistically different (p > 0.05). No effect of IVF technique was seen on the success rate (6%) in each group.