The spatial distribution of maize plants influences the number of kernels set per plant by modifying the radiation environment during the critical period for kernel number determination. A two-year field experiment was conducted in Sardinia to explore whether, in a Mediterranean environment, a reduction in row distance can have a positive effect on grain yield of full-season maize hybrids and, if it does, whether this effect is also affected by plant density. Treatments were a factorial combination of three plant densities (6, 8 and 10 plants/m2) and two row spacings (35 and 70 cm). Grain yield and grain number benefited from a reduction in row distance from the canonical 70 cm to 35 cm irrespective of plant density and yield level (14.7 t/ha on average in 2021, 9.9 t/ha in 2022 vs 13.7 and 8.8 t/ha with canonical row distance). Row distance did not affect either the coefficient of extinction of radiation or the intercepted photosynthetically active radiation (PAR) during the critical period for grain number determination. The higher grain number per unit area at the smaller row distance translated into a greater grain yield, which cannot solely be attributed to radiation interception and plant growth rate during the period of kernel number determination. Halving the common row distance is a valuable management option for full-season hybrids grown in Mediterranean environments without nitrogen and water limitations as it seems capable of increasing grain yield via an increase in kernel number per unit area, regardless of plant density and yield level.

Smallholders in Southern Africa continue to grapple with low maize productivity despite this being the staple food crop. This study sought to analyze and isolate the relative contribution of agronomic practices to maize yields obtained by smallholders in Malawi and Mozambique using data generated from on-farm trials testing the performance of conservation agriculture cropping systems. The trials were implemented in two communities, namely Kasungu district in Malawi and Sussundenga district in Mozambique, and ran for seven consecutive growing seasons starting in 2010–2011. Maize yield was measured annually in the on-farm trials, which included a ‘control treatment’ representing an improved farm practice, and in neighboring fields managed by the same farmers on their own, hence representing a ‘true farm practice’. Results indicated that maize yield increased linearly with increasing plant population at harvest at both sites. On average, an increase in plant population at harvest by 1000 plants ha–1 resulted in an increase in maize yield of 90 and 63 kg ha–1 at Kasungu and Sussundenga, respectively. The greatest maize yields were obtained when plant population at harvest exceeded 40 000 plants ha–1. Yet, the plant population at harvest was below the generally recommended optimum for most of the cropping systems studied and in most growing seasons. Furthermore, the use of agronomic practices alone without conservation agriculture (i.e., improved varieties, fertilizer management, and timely weed control) resulted in maize yield gains of as much as 54% and 43% relative to the ‘true farm practice’ at Kasungu and Sussundenga, respectively. Overall, the proportion of these yield increases relative to the ‘true farm practice’ accounted for by agronomic practices amounted to 53–70% and 57–85% at Kasungu and Sussundenga for the highest to the lowest-yielding cropping system. Although conservation agriculture significantly improved maize yield at both sites, such increases were smaller in magnitude compared to the yield gains derived from improved agronomic practices. The study suggests that considerable strides toward narrowing maize yield gaps in Southern Africa can be achieved through improvement of current crop management practices, let alone adhering to the conservation agriculture principles of minimum tillage, residue retention, and crop diversification.

Plant responses to multiple environmental conditions in the habitat are characterized by intra-species variety. Ferula assa-foetida L. is a native medical plant in Iran, which has a wide range of therapeutic and pharmacological properties. The objective of the current study was to identify changes in phenolic content, antioxidant capacity and essential oil (EO) composition in different tissues (leaf, flower and fruit) of three populations of F. assa-foetida L. (Sarbisheh, Nehbandan, located in South Khorasan province of Iran). The results showed that total phenolic content (TPC), total flavonoid content (TFC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity in the leaves of Sarbisheh were higher than in other treatments. The amount of TPC, TFC and DPPH scavenging activity in leaves was higher than in other tissues in the Sarbisheh population, increasing by 31 and 70%, 41 and 20%, 8 and 13%, respectively, over that of flowers and fruits. The main EO compounds of leaves were α-pinene (11.86–13.56%), β-pinene (6.80–7.99%), bornyl acetate (15.80–17.33%). The main EO constitutes of flowers were Z-propenyl-sec-butyldisulfide (10.12–12.4%), eco-fenchyl acetate (10.87–12.4%), myrcisticin (13.43–15.87%) and α-bisabolol (11.23–13.76%). The primary compounds of fruit EO were β-pinene (9.32–11.26%), (Z)-1-propenyl sec butyldisulf (17.54–18.87%) and (E)-1-propenyl sec butyldisulf (28.32–30.02%). The agglomerative hierarchical clustering showed that three distinguished clusters were identified for population, where Nehbandan and Qaen had the higher similarity and Sarbisheh completely differed from the two ones. Different plant tissues contain varying types of chemicals, with leaves exhibiting higher levels of phenolic content and antioxidant capacity. This characteristic can be beneficial for industries such as food and pharmaceuticals.

The availability of postemergence grass control herbicides can prevent dependence on potentially unnecessary preemergence herbicides. No postemergence grass control herbicides have federal registration for kenaf in the United States. This research was conducted to collect data to support such registration. Clethodim, fluazifop, quizalofop, and sethoxydim applied at three rates did not injure established kenaf, reduce plant populations, reduce plant heights, or reduce stalk yields.

Sweet corn is seeded under a wide range of population densities; however, the extent to which variable population density influences weed suppression is unknown. Therefore, field studies were undertaken to quantify the influence of sweet corn seeding level on growth, seed production, and post-harvest seed germination of wild-proso millet, one of the most problematic weeds in the crop. As crop seeding level increased, path analysis results indicated the crop canopy became taller and thicker, resulting in less wild-proso millet biomass, seed production, and germinability. However, at the level of individual fields, reductions in wild-proso millet growth and seed production were modest, at best, between a crop population currently used by growers and a higher crop population known to optimize yield of certain hybrids. These results indicate near-future increases in sweet corn seeding levels may play a minor role in improving weed management in individual sweet corn fields. Nonetheless, a reduction in crop populations, via weather- or management-driven phenomenon, increases risk of greater wild-proso millet seed production.

Greenhouse and field experiments were conducted to investigate the effect of glyphosate rate and degree of glyphosate spray coverage on pitted morningglory control. Pitted morningglory in the two-, four-, and six-leaf growth stages were treated with the isopropylamine salt of glyphosate at 0.28, 0.56, 0.84, 1.12, 1.40, and 1.68 kg ai/ha. Two- and four-leaf plants were controlled 98% with 1.68 kg/ha glyphosate, whereas six-leaf plants were controlled 68%. Control of two-, four-, and six-leaf plants with the commonly used field rate of 1.12 kg/ha was 68, 60, and 50%, respectively. In a separate greenhouse study, four-leaf pitted morningglory plants with 0, 33, 66, or 100% of their total leaf area exposed to herbicide spray were treated with 0.84, 1.68, or 3.36 kg/ha glyphosate. Increasing glyphosate rate from 0.84 to 3.36 kg/ha increased control from 36 to 88%. In contrast, increasing percent leaf exposure to glyphosate from 0 to 100% increased control from 57 to 75%. Increasing glyphosate rate from 0.84 to 1.68 kg/ha always improved control. However, increasing glyphosate rate from 1.68 to 3.36 kg/ha was beneficial only when no leaves were exposed to the spray solution. In the field, glyphosate spray coverage decreased from 85 to 40% as plant density increased from 1 to 32 plants/m2. However, control decreased only 11% (90 to 79%) between the highest and lowest levels of glyphosate spray coverage. These results demonstrated that inadequate control of pitted morningglory with glyphosate was more related to tolerance than glyphosate spray coverage. Glyphosate rates higher than 1.68 kg/ha may be beneficial when spray coverage is severely limited or when plants are beyond the four-leaf growth stage.

Studies were conducted in 2005 and 2006 at three Iowa locations to determine the effect of soybean seeding rate and glyphosate application timing on weed management and grain yields in glyphosate-resistant soybean. End-of-season weed populations were affected by soybean seeding rate at only one location, with higher weed densities present in the lowest seeding rate when glyphosate was applied at the V2 soybean growth stage. Although weed populations were not consistently affected by soybean population, weed biomass present at soybean harvest was inversely related to soybean population. At the location with the highest weed populations, no single glyphosate application provided yields equivalent to the weed-free control. At the other locations, glyphosate application timing did not affect soybean yield. Lower soybean yields occurred with 240,000 seed/ha compared with 420,000 seed/ha at all locations and with 300,000 seed/ha at two locations.

Research was conducted to determine the effect of planting pattern, plant density, and levels of weed management intensity on intercepted photosynthetically active radiation (IPAR), weed control, and cotton lint yield in glyphosate-resistant cotton. Twin-row planting pattern canopy IPAR was 55% 7 wk after emergence (WAE) and 76% 9 WAE compared to 48% for single-row planting pattern 7 WAE and 59% 9 WAE. Regardless of cotton density, row spacing, or weed management intensity, control of browntop millet and Florida beggarweed was at least 88% 18 WAE. Benghal dayflower, sicklepod, and smallflower morningglory control was greater in twin-rows compared to single-rows at a cotton density of 7 plants m−2. Control of Benghal dayflower and sicklepod increased when cotton density increased at low weed management intensities; however, cotton density had no effect on weed control at higher levels of weed management input. At a cotton plant density of 7 plants m−2, twin-row cotton yielded 220 kg ha−1 more than the single-row planting pattern. Data indicates twin-row cotton production is feasible and that control of various weeds was better in twin-row than single-row pattern at lower cotton density and weed management intensity.

Amphibian populations have been declining worldwide, with multiple potential causes. At La Selva field station in north-eastern Costa Rica, previous work has shown that populations of many amphibians have decreased significantly since the 1970s, especially in primary forest. Starting in 1998, we investigated one of the most common frog species at La Selva, the poison-dart frog Oophaga pumilio (= Dendrobates pumilio). In a survey of 50 plots of 100 m2 in 1998, adult frogs were 4.6 times more abundant in secondary forest than in primary forest. Tadpoles were found only in secondary-forest plots. Almost all (89%) of the tadpoles were found in leaf axils of Dieffenbachia spp., which were much more abundant in secondary-forest than in primary-forest plots. The greater abundance of Dieffenbachia spp. in secondary forest was confirmed in a broad survey of ~11 km of trails within La Selva in 2002. When the same trails were resampled in 2012, Dieffenbachia spp. had been extirpated from 72% of the 50-m segments where plants were present in 2002; abundance was greatly reduced in the few trail segments where any Dieffenbachia spp. remained in 2012. The loss of Dieffenbachia spp., especially in secondary forest, removed the species most often used by O. pumilio for tadpole rearing. Based on counts of calling frogs in 2010, there was no difference in O. pumilio abundance in primary versus secondary forest, in striking contrast to multiple earlier surveys that found much greater frog abundance in secondary forest. We propose that the reason for the rapid decline in Dieffenbachia spp. is herbivory by the collared peccary (Pecari tajacu), which has increased in abundance at La Selva in recent years. A likely consequence is continued reduction in O. pumilio populations.