Effect Of Cutting On Yield And Photosynthetic Physiological Characteristics Of Sweet Sorghum In The Yellow River Delta

The Yellow River Delta is the broadest estuarine wetland ecosystem in the warm temperate zone of China.Because of its high degree of soil salinization,it severely restricts the development of agriculture and animal husbandry.Planting salt-tolerant crops is an effective method to utilize saline-alkali land.Cutting is one of the regulation methods in agricultural production.Cutting period as well crop variety are the key factors affecting the yield and quality of pasture.Therefore,suitable cutting period and varieties play an important role in maintaining high and stable yield of plants.In order to find out the physiological response of sweet sorghum to castration,this study was conducted in 2017-2018 using a combination of field experiments and laboratory experiments.The effects of different cutting times on the yield of sweet sorghum and the quality of forage were studied.The changes of light energy utilization ability of sweet sorghum during the growth process were analyzed.This study can provide the corresponding technical reference for the planting of sweet sorghum and the improvement of saline-alkali land in the Yellow River Delta.The main results are as follows:1.Screening of sweet sorghum varieties suitable for Cutting in the Yellow River DeltaIn this experiment,7 sweet sorghum varieties including jitianza-2,A82,A73,F438,A60,A85 and F968 were planted in the field.According to the differences in yield,sugar content and agronomic traits at harvest time,we finally screened out three varieties,Jitianza-2,A82 and A73,which have high yield,strong resistance and good commerciality.Therefore,they can be further popularized and applied in the Yellow River Delta.In order to explore the effects of cutting times on the yield of sweet sorghum stalk,available nutrients and the yield of washing fiber,we carried out different cutting times: cutting 3 times(A1+A2+A3),cutting 2 times(A1+A2 '),cutting 2 times(B1+B2)and cutting only once(C1).Because of the large difference in biomass between sweet sorghum harvested at different stages,there are also significant differences in the yield of various nutrients.The best harvesting plan was found from the point of biomass and crude protein yield of our three varieties: when cutting twice(B1+B2),the yield of stalk and nutrient components of Jitianza-2 were more considerable.2.Effects of different cutting periods on the yield and nutrients composition of sweet sorghumIn this part of field experiment,the effects of different cutting stages on the yield and quality of sweet sorghum were studied by using three different cutting periods(August 30,September 20 and October 10)in the growing period.The results showed that the stalk yield of sweet sorghum was basically stable after September and there was no significant increase.Crude protein,crude fiber,crude fat and nitrogen-free extract all showed a trend of increasing yield with the growth period,while the yield of coarse ash increased first and then decreased.In addition,neutral washing fiber,acid washing fiber and hemicellulose showed a trend of higher yield with the maturity of sweet sorghum.Therefore,it is not necessary to wait until the grain matures to reach the maximum biomass during the growth period,and the crude protein yield is also high,before the first ten days of October,when the best harvest time for sweet sorghum can ensure its feed quality.3.The effect of cutting on the light energy utilization ability of sweet sorghum during the growth recoveryIn this part of the experiment,we used the cutting time determined in the first part to study the effect of cutting on the light utilization ability of Sweet Sorghum in the process of restoring growth.The results showed that the relative content of chlorophyll and carotenoid decreased compared with that before cutting,and the relative content of anthocyanin could be restored to the level before treatment in a short time.The net photosynthetic rate almost returned to the pre-treatment level at 18 days after cutting.In addition,cutting had no effect on the shape of the fast chlorophyll fluorescence induction kinetics curve.There was no difference in the initial fluorescence(Fo)of leaves,and the maximum fluorescence(Fm)increased gradually with the recovery time.After cutting,the light energy absorbed per unit area of the blade and the light energy captured per unit area decreased,the heat dissipation per unit area did not change,and the quantum yield of electron transfer per unit area decreased.The activity of PSI is almost unaffected.After cutting,the heat dissipation pattern of sweet sorghum changed,and the proportion of qE in the leaves decreased,while the proportion of qT and qI increased.