<p>Due to the violation of the technology of sunflower growing in Ukraine and the disbalance of scientifically grounded crop rotation, or their complete absence, with the expansion of sunflower seeds in the structure of crops to 40% and more, and the simplification of the system of basic cultivation of arable land, accompanied by a sharp increase in perturbation of crops by autotrophic and parasitic weeds. To determine the impact of agrotechnical measures, saturation of sunflower seeds, soil tillage systems, and fertilization on the number and species composition of various agrobiological groups of weeds in sunflower crops, including <em>Orobahche cumana</em> Walls. To reduce the herbicide (chemical) loading in agrophytocoenoses of oilseed crops, and ecologization of protection from weeds it was supposed to reveal optimal and environmentally friendly parameters of modern elements of sunflower cultivation technology. The scheme of the experiment included two grains–steam–breeding and grain–seed crop rotations with saturation in the structure of sunflower seeding 12.5%, 20% and 33.3%; three cardinally different systems of basic cultivation of the ground (filed plowing, differentiated and systems of mulching and no-till); two fertilizer systems (no fertilizers + post–harvest residues, N30–60P30–45K30–45 + post–harvest residues). All other elements of agrotechnics were standard and generally accepted for the steppe zone. The accounting of obstinacy was carried out by quantitative–weight and species–specific methods. A tendency has been observed to increase the number of weeds before the first inter–row treatment for mulching and no-till and direct sowing (10.4–15.1 pcs/m<sup>2</sup>) in 1.3–1.5 times compared with the filed plowing (7, 1–12.4 pc. /m<sup>2</sup>). At the time of harvesting in comparison with the spring definition, the infestation of oilseed crop under fertilized background decreased by 1.6–4.2 times; and their quantitative values were 2.6–5.2 pcs/m2 (field plowing), 4.1–8.1 (differentiated tillage), 5.5–12.4 pcs/m<sup>2 </sup>(no-till), indicating the preservation of regularities inherent in the spring period. It was established that the air–dry weight of weeds (within the limits of individual terms of the definition) varied in versions directly proportional to the change in quantitative values, and on average slightly higher for mulching and no-till (3.8–15.7 g/m<sup>2</sup>) than filed plowing (1.8–12.3 g/m<sup>2</sup>). It was proved that the degree of manifestation of the active biological phase of the vaginal parasitism naturally increased with the reduction of the time interval of sunflower return in crop rotation, especially in 3–way crop rotation (33.3% sunflower) – 6.9–12.7%, that is, each sunflower field in the crop rotation – an additional resource for the accumulation of Broomrape in the soil. The increase in the degree of sunflower damage with sunflower wool (up to 11.0–12.7 pcs/100 plants) was observed on the background of deep plowing and decreased with a decrease in the depth of main cultivation in shallow and direct sowing by 6.9–7.8%, or 1.6 times as a result of the localization of the Broomrape in the ground beside the sunflower roots, which provokes its germination with its root secretions, while the seeds of Broomrape for mulching and no-till are located on the top of the soil, soil surface or plant residues, that make impossible its germination in a more dense soil in the absence of the root system of host plant (sunflower). Maximum seed yield (2.35–2.82 t/ha) was obtained in 8–crop rotation at the concentration of sunflower in the seed structure of 12.5%. Extension of the sown area to 25% and 33.3% contributed to a decrease in yields of 2.14–2.67 and 2.10–2.56 t/ha, or 8.9–5.3% and 10.0– 9.2% due to the increase in the degree and intensity of damage to plants by Broomrape. Thus, the expansion in the structure of sunflower crops to 33.3% and the minimization of the main cultivation of the soil leads to an increase in perishability by autotrophic weeds in 1.3–1.5 times, and the degree and intensity of damage by Broomrape, on the contrary, decreases on the finely treated agrofons regarding the localization of seeds in the upper layer of soil or on plant residues, which makes it impossible to germinate.</p>
Impact of extreme drought and incentive programs on flooded agriculture and wetlands in California’s Central Valley