RESUMO
Corn (Zea mays) biomass accumulation and nutrient uptake by the six-leaf collar (V6) growth stage are low, and therefore, synchronizing nutrient supply with crop demand could potentially minimize nutrient loss and improve nutrient use efficiency. Knowledge of corn's response to nutrient stress in the early growth stages could inform such nutrient management. Field studies were conducted to assess corn recovery from when no fertilizer application is made until the V6 growth stage, and thereafter, applying fertilizer rates as those in non-stressed conditions. The early season nutrient stress and non-stress conditions received the same amount of nutrients. As the availability of nutrients for plant uptake is largely dependent on soil moisture, corn recovery from the early season nutrient stress was assessed under different soil moisture regimes induced via irrigation scheduling at 50% and 80% field capacity under overhead and subsurface drip irrigation (SSDI) systems. Peanut (Arachis hypogaea) was the previous crop under all conditions, and the fields were under cereal rye (Secale cereale) cover crop prior to planting corn. At the V6 growth stage, the nutrient concentrations of the early season-stressed crops, except for copper, were above the minimum threshold of sufficiency ranges reported for corn. However, the crops showed poor growth, with biomass accumulation being reduced by over 50% compared to non-stressed crops. Also, the uptake of all nutrients was significantly lower under the early season nutrient stress conditions. The recovery of corn from the early season nutrient stress was low. Compared to non-stress conditions, the early season nutrient stress caused 1.58 Mg ha-1 to 3.4 Mg ha-1 yield reduction. The percent yield reduction under the SSDI system was 37.6-38.2% and that under the overhead irrigation system was 11.7-13%. The high yield reduction from the early season nutrient stress under the SSDI system was because of water stress conditions in the topsoil soil layer. The findings of the study suggest ample nutrient supply in the early season growth stage is critical for corn production, and thus, further studies are recommended to determine the optimum nutrient supply for corn at the initial growth stages.
RESUMO
Application of insecticides for stink bug management through overhead irrigation, also called chemigation, could reduce application costs, soil compaction, and applicator exposure, while enabling growers to treat multiple fields simultaneously. The objective of these laboratory experiments was to compare knockdown, survival, and efficacy of insecticides when appropriately diluted for ground sprayer and chemigation applications. Treatments included water, bifenthrin [0.11 kg (AI)/ha] and dicrotophos [0.56 kg (AI)/ha] diluted for a ground sprayer (93.5 liters/ha), bifenthrin and dicrotophos diluted for chemigation (25,396 liters/ha), and bifenthrin and dicrotophos plus adjuvants diluted for ground sprayer or chemigation. Two- to 14-day-old adults of Nezara viridula (L.), Euschistus servus (Say), and Halyomorpha halys (Stål) were briefly submerged in appropriately diluted insecticides and then introduced into a disposable petri dish with or without food. Dishes were placed in a growth chamber provisioned with digital video cameras to monitor knockdown and feeding after insecticide exposure. Knockdown was visually assessed at 24 h after treatment followed by mortality and recovery from knockdown at 48 h after treatment. All stink bugs were knocked down within 1 h and never recovered when exposed at ground sprayer dilutions. However, many bugs survived chemigation dilutions. Less than half of the stink bugs were knocked down when exposed to dicrotophos (with or without adjuvants) and survival ranged from 17 to 77%, compared to 7-90% survival when exposed to bifenthrin at chemigation dilutions. These results strongly suggest that chemigation applications for stink bug management need to be closely examined.
