اثر کشت بی‌خاک‌ورزی بر عملکرد شبدر برسیم در کشت تاخیری در مزارع بذری شمال خوزستان

Background and Objective: Berseem Clover (BC) is a forage plant in the legume family, the cultivation of which has attracted the attention of farmers in recent decades. The area under cultivation of BC for seed production in the northern Khuzestan province is 1,000 hectares, which has shown higher yields compared to other regions of the country. This region has a higher seed yield compared to other regions of the country, and due to the high seed quality, it has long supplied the seeds needed by different regions of Iran, especially the northern provinces of the country. According to research conducted at the Safi-Abad Agricultural and Natural Resources Research and Education Center in Dezful, the best recommended planting date for BC in Khuzestan is mid-October. However, due to the presence of summer crops in most farms in northern Khuzestan and their harvest in November and December, BC planting is usually delayed in these areas. Additionally, early autumn rains and the inability to prepare land after rainfall further contribute to delays in planting BC. In addition, early autumn rainfall and the inability to prepare land after rainfall usually cause further delays in BC planting. On the other hand, in Khuzestan, unfortunately, the wheat-corn or wheat-rice monoculture system in most agricultural lands and the failure to plant a legume plant such as clover has caused a decrease in soil organic matter, a decrease in wheat, rice, and barley yields, weed spreading and diseases, and a decrease in water productivity. As a result, in order to restore soil and water resources and have a sustainable agriculture, the use of conservation agriculture can play an important role in protecting soil and water resources and production sustainability. Therefore, the present study was conducted with the aim of investigating the possibility of late planting of BC with NT method on the forage and grain corn residues (the dominant summer crop in northern Khuzestan) in the conditions of northern Khuzestan to include berseem clover in the rotation of the region.
Materials and Methods: This research aimed to evaluate the feasibility of delayed planting of BC through three experiments (with different planting beds) arranged as split plots within a randomized complete block design with three replications at Safiabad Agricultural and Natural Resources Research and Education Center, over two agricultural years (2019-2020 and 2020-2021). The three experiments included: BC planting after summer fallow on the recommended planting date for BC (Experiment 1), BC planting after harvesting summer forage corn (Experiment 2), and BC planting after harvesting summer grain-corn while preserving residues (Experiment 3). In each experiment, the main factor was two tillage methods: conventional tillage (CT) and no-till (NT), while the sub-factor consisted of three seeding rates including 20, 25, and 30 kilograms per hectare.
In two years of experiment, a suitable plot of land was selected from the fields of the Safi Abad Agricultural Research and Education Center in Dezful and two-thirds of it was allocated for planting corn in the first month of August and one-third for fallow. For CT method (first experiment), land preparation including plowing, disking and leveling and for cultivation a modified Barzegar-Hamedan planter with three rows on a 75 cm ridge was used. However, in the second and third experiments without land preparation operations, BC was planted on 75 cm ridges with a No till planter (at the studied seeding rates).
The planting date in the three mentioned experiments was in the second decade of October (the traditional planting date of the region), the third decade of November and January, respectively. In the third experiment, due to the delay in corn harvest (corn harvest in the region is also delayed from December to January due to high moisture content of corn grain and possible rainfall), it was not possible to harvest clover forage and sward, but in the first and second experiments, was sward twice before sowing. The measured traits included BC seed yield, the number of seeds per inflorescence, the number of inflorescences per square meter, thousand seeds weight, and the amount of fresh and dry forage produced BC. After conducting the experiment and obtaining data related to the desired traits, variance analysis was performed using SAS software (version 9.2) and the means of the studied treatments were compared using Duncan's multiple range test at a probability level of 5%.

Results: Before performing the combined analysis of variance in the first experiment, Bartlett's test was used to ensure the uniformity and homogeneity of error variances in the two years of the experiment. The results of the Bartlett test for all studied traits indicated the homogeneity of experimental error variances. The results of the three experiments showed that NT in the first experiment caused a 34% decrease in the BC seed yield. In the second experiment there was no significant effect on the BC seed yield, and unlike the first experiment. In the third experiment NT method increased the BC seed yield by 66% compared to the CT method. The results of the effect of the seed rate on the seed yield in the first experiment showed that the highest seed yield (1139 kg/ha) belonged to the treatment of 25 kg of seed per hectare, but in the second and third experiments different seed rate did not have a significant effect on the BC seed yield.
Conclusion:
The results showed that direct sowing of BC in the residues of summer crops such as corn and rice, which are harvested from November to January, in addition to increasing the yield of BC seeds, was also effective in preserving soil organic matter, speeding up planting operations, improving the physical and chemical properties of the soil, preventing soil erosion, maintaining soil moisture, and reducing planting costs. Therefore, considering the advantages of the NT method, it is necessary to change the tillage system from CT to NT with residue preservation for the sustainable development of the agricultural sector in the Khuzestan region.