Effects of Meteorological Factors on Overwintering Ability, Yield and Quality of Forage Rape

Yao ZHANG Junzhu GE Guangsheng ZHOU Xidong WU Yong an YANG Haipeng HOU Qian LIANG Zhiqi MA

Abstract In order to investigate the effects of meteorological factors on rape overwintering ability, forage yield and quality of rape in the North China plain, Brassia campestris L. and Brassica napus L. were used in this study. The results showed that compared with the B. napus L. varieties, the growth period of B. campestris L. was shortened by 10-15 d, the overwintering rate (WR) increased by 50.6%, and the density after winter (PD) increased by 41.5%. The fresh forage yield (FFY) and dry forage yield (DFY) of the B. campestris L. type significantly increased by 40.9% and 38.1% compared with the B. napus L. type., respectively, while the forage quality of the B. napus L. type rape was significantly better than that of the B. campestris L. type. Compared with the B. campestris L. type, the crude protein (CP), fat, ash and total fatty acid (TFA) contents of the B. napus L. type of rape increased by 27.6%, 42.9%, 23.9% and 52.3%, respectively, and the milk productivity (HM), relative forage value (RFV) and relative forage quality (RFQ) increased by 14.0%, 16.2% and 42.1%, respectively. The light and heat resources before wintering increased the WR and PD (P<0.05), and were positively correlated with FFY and DFY (P>0.05), and lower temperature during the wintering period led to lower WR (P<0.01). The light and heat resources during the overwintering period and after regreening were negatively correlated with FFY and DFY (P>0.05). The contents of CP, fat and TFA of rape had an extremely significant negative correlation with the temperature and sunshine hours before wintering, but an extremely significant positive correlation with the temperature during the wintering period and after regreening, as well as the sunshine hours and rainfall during the wintering period; and HM had an extremely significant positive correlation with the temperature, sunshine hours and rainfall during the wintering period, while RFV and RFQ were only extremely significantly positively correlated with the maximum temperature and rainfall. In summary, in the North China Plain, for autumn sowing rape, the B. campestris L. type can be selected to improve the wintering rate, and the B. napus L. type should be the main choice to improve the forage quality of rape. Therefore, the B. napus L. variety HYZ62 can be selected for autumn sowing in the North China Plain.

Key words Forage rape; Meteorological factors; Wintering ability; Forage yield; Forage quality

Received: January 12, 2021  Accepted: March 23, 2021

Supported by National Key Research and Development Program of China (2017YFD0200808); Seed Science and Technology Major Special Program of Tianjin (18ZXZYNC00100); Scientific Research Program (Natural Science) of Tianjin Education Committee (2019KJ039); Graduate Research Innovation Program of Tianjin (2020YJSS128).

Yao ZHANG (1997-), male, P. R. China, master, devoted to research about stress-resistance cultivation of rape.

Corresponding author. Junzhu GE. E-mail: gjz0121@126.com.

China is one of the biggest country in rapeseed production, with planting area and outputting for about 25% of those in the world. Forage rape were began to test and applicated by the team of Academician Fu Tingdong of Huazhong Agricultural University in the 1980s［1］. In recent years, forage rape has been planted in different ecological areas in China, because of the wide range of adaptability［2-6］. Forage rape has high total energy and crude protein content, low neutral detergent fiber content［7］, and crude protein yield were higher than legume forage crops［8］, and thus can alleviate the problem of insufficient green fodder for the animal husbandry development. Cultivation measures such as seeding rate, nitrogen application, sowing date and so on, can significantly increase the rape forage yield. The seeding rate can increase the multiple-cropping rape yield by increased leaf area index and population assimilation rate［9-10］. The rape biological yield and dry matter accumulation were increased with nitrogen application increased［11］. Early Sowing can extend forage rapes light and temperature time and so increase nutrient accumulation and improve silage quality［9］. Forage yield and forage quality of rape could be regulated by harvest time, and research shows that the forage yield at flowering stage is the highest［10-12］, while crude protein and crude fat contents are the highest at initial flowering stage, because the crude fiber content increases after the flowering stage, which can reduces the feeding quality［13］. The adjustment of the sowing date and harvest time can regulates the temperature, light and rainfall during the rape growth period, and rape reproductive growth period was prolonged by the low temperature after flowering［14］. Rapeseed yield decreases by 0.74%-2.92% and 1.64%-13.61%, respectively, by the temperature increased 1 ℃ and rainfall increased 10 mm［15］. The comprehensive regulation of varieties, plant protection, sowing date, fertilizer management, and plant density can improve the stability of rape production under climate change［16］. Temperature and light are two important factors that affect the rape yield and quality, but the existing research mainly focuses on the use of rapeseeds and oil extraction, and there are few reports on the research of forage rape. In recent years, the animal husbandry industry in the North China Plain has developed rapidly, and the planting structure has undergone the structural adjustment of "grain-to-forage". Forage rape has gradually developed as a beneficial supplement. However, there were lack of research on the autumn sowing rape could survive safely the winter and forage yield and quality formation mechanism. Therefore, in this study, two Brassia campestris L. varieties and three Brassica napus L. varieties were selected to study the effects of meteorological factors on the autumn sowing rape wintering characteristics, and the forage yield and quality in the North China Plain, so as to provide theoretical support for the forage rape development in this region.

Materials and Methods

Experimental design

The field experiment was conducted from September 2019 to May 2020 at the Tianjin High-quality Agricultural Products Development Demonstration Center. The experiment adopted single-factor randomized block design. The varieties used were B. campestris L. Longyou 12 (LY12) and Tianyou 12 (TY12), and B. napus L. Huayouza 62 (HYZ62), Shiyou 2 (SY2) and Huayouza 158 (HYZ158). The rapeseeds were planted on September 24, 2019, with a large area setting, 300 m2 per plot, and a seeding rate of 7.5 kg/hm2, which planted by wheat plot planter and the seeds were mixed with fine sand, the row space is 40 cm. Before planting, ground preparation was performed, and 300 kg/hm2 compound fertilizer (N-P2O5-K2O, 25%-10%-16%) was used as bottom fertilizer, and 45 kg/hm2 N was applied at the buddingbolting stage. Other field management adopted the ordinary field management mode.

Determination items and methods

Meteorological data

The rape growing season daily meteorological data including average temperature (Tav, ℃), maximum temperature (Tmax, ℃), minimum temperature (Tmin, ℃), sunshine hours (SHs, h), rainfall (RF, mm), were from the weather stationb(Fig. 1), and growth degree days (GDD, ℃·d) calculated based on the biological temperature of rape at 0 ℃.

Results and Analysis

Growth period and meteorological factors

The seedling date of the B. campestris L. varieties was 3 d earlier than that of the B. napus L. varieties, and the reviving dates were 6-13 d earlier (Table 1). TY12 revived the earliest, 4-13 d earlier than other varieties, and HYZ158 was the latest, 3-13 d later than other varieties. The durations from reviving to budding stage and from bud appearing to initial flowering among varieties were 27-29 d and 8-10 d, respectively, and there were no significant differences among varieties. However, from initial flowering to harvest (the end of the full-bloom stage), the B. campestris L. varieties were shorter than the B. napus L. varieties by 1-6 d. The whole growth periods of the B. campestris L. varieties were 10-15 d shorter than those of the B. napus L. varieties. The durations from reviving to harvest in the B. campestris L. varieties were 3-5 d shorter than the B. napus L. varieties. TY12 had the shortest growth duration, which is 212 d, while HYZ158 had the longest growth duration, which is 222 d.

Due to the differences of growth duration, the meteorological factors varied in each growth stage (Table 2). The temperature conditions of the B. campestris L. varieties before wintering were better than those of the B. napus L. varieties, and the growth degree days (GDDs) and the sunshine hours (SHs) increased by 35.1 ℃·d and 9.5 h, respectively. As the B. campestris L. varieties revived earlier, the GDDs below 0 ℃ from wintering to reviving were significantly higher than those of the B. napus L. varieties, increasing by 24.9-53.5 ℃·d, while the SHs decreased by 43.60-82.00 h (P<0.05), and the rainfall (RF) decreased by 2.80-15.50 mm. Compared to the B. napus L. varieties, the GDDs of the B. campestris L. varieties decreased by 130.10-178.80 ℃·d, the SHs decreased by 6.3-28.9 h, and the RF decreased by 25.3-38.00 mm, because of the duration from reviving to harvest of B. campestris L. varieties were shortened by 3-5 d.

Yield and agronomic traits of forage rape and their correlation with meteorological factors

Table 3 showed that the fresh forage yields (FFY) and dry forage yields (DFY) of different  varieties rapes were significantly different. The yield of TY12 was the highest, while the yield of HYZ158 was the lowest. Compared with HYZ158, the FFY of other four varieties increased by 35.0%, 136.0%, 64.9% and 30.0%, respectively, and the DFY increased by 33.9%, 124.6%, 52.3%, and 37.1%, respectively. The wintering ability of the B. campestris L. varieties was significantly better than that of the B. napus L. varieties, and the wintering rate increased by 50.6%. The highest wintering rate was observed in TY12, being 40.0%, and the post-winter density was 619 500 plants/hm2, while HYZ158 had the lowest wintering rate of only 23.6%, and it post-winter density was 388 900 plants/hm2. The plant heights of the B. campestris L. varieties were significantly higher than those of the B. napus L. varieties by 30.8%. The plant height of TY12 reached 124.8 cm, and that of HYZ158 was only 81.3 cm.

The correlation between the yield and agronomic traits of different types of rape and meteorological factors was analyzed (Table 4). Forage rape FFY and DFY were positively correlated with the temperature and sunshine hours before winter (P>0.05), which was because that the wintering rate, post-winter density, and plant height of rape were significantly positively correlated with the temperature and sunshine hours before winter, indicating that both the increase of temperature and the extension of sunshine hours could significantly increase the wintering rate of rape, thereby increasing the post-winter density and increasing the plant height. The reason might be that the long light time and sufficient heat resources before winter could promote the accumulation of sugar before the wintering period of rape, and ensure the physiological function requirements of rape wintering period. Forage rape FFY and DFY had a negative correlation with the temperature and sunshine hours in the wintering period (P>0.05), which was because that the temperature and sunshine hours in the wintering period were in an extremely significant negative correlation with the wintering rate, post-winter density and plant height of rape, and wintering rate and post-winter density decreased significantly due to the decrease in temperature and the shortening of sunshine hours during the wintering period. It might be due to that the increase in temperature and the extension of light duration during the wintering period would lead to potential physiological changes in the growth of rape, the physiological damage would be strengthened in case of low temperature (below -10 ℃), the freezing death rate would increase, and the wintering rate would decrease, so the density after reviving would decrease. After reviving, the forage rape plant height had a significant negative correlation with temperature, sunshine hours and rainfall, indicating that the increases in temperature and growth degree days, the extension of sunshine hours and the increase of rainfall had side effects on rapes plant height, resulting in the significant negative correlation between temperature and rainfall after reviving and FFY and DFY. Specifically, FFY fresh forage yield was in an extremely significant negative correlation with sunshine hours after reviving.

Forage rape silage quality and its correlation with yield and meteorological factors

Analyzing the silage quality components of different types of forage rape (Table 5) showed that, the crude protein (CP), fat, ash and total fatty acid (TFA) contents of the B. napus L. varieties were significantly higher than those of the B. campestris L. varieties, increasing by 27.6%, 42.9%, 23.9% and 52.3%, respectively, while the acid detergent fiber (ADF) and neutral detergent fiber (NDF) significantly decreased by 9.7% and 9.5%, respectively. Evaluating comprehensively, the silage quality of the B. napus L. type was significantly better than that of the B. campestris L. type, and the milk productivity (HM), relative forage value (RFV) and relative forage quality (RFQ) increased by 14.0%, 16.2% and 42.1%, respectively.

The analysis showed that there were no differences in crude protein and total fatty acids contents between LY12 and TY12, which were significantly lower than HYZ62, SY2 and HYZ158. The ADF and NDF contents of LY12 and TY12 were significantly higher than HYZ158. TY12 had the lowest lignin content (P<0.05), and starch, fat and ash contents significantly lower than other 4 varieties. There were no significant differences in total digestible nutrients (TDNs) among the varieties. Due to the differences in silage quality traits, HYZ158 had the best comprehensive evaluation of silage quality, with the highest HM, RFV and RFQ, among which RFV and RFQ were significantly higher than other 4 varieties.

The forage rape silage quality traits correlation analysis showed that (Table 6), the crude protein content had a significant negative correlation with ADF and NDF, and a significant positive correlation with fat content; ADF only had an extremely significant positive correlation with NDF; the fat content had an extremely significant positive correlation with ash content and TFA; and the correlation between other forage quality traits had no significant level.

Analyzing the evaluation indexes of forage rape silage quality showed that crude protein content played an extremely significant positive roles on milk productivity, relative forage value and relative forage, which indicated forage rape high silage quality by the higher crude protein content. However, milk productivity, relative forage value, and relative forage quality had an extremely significant negative correlation with ADF and NDF contents, which indicated forage rape high silage quality by the lower rape fiber content. Meanwhile, milk productivity and fat content were extremely significantly positively correlated, indicating that the increase in fat content could significantly increase the milk productivity of forage rape, but had no effect on the relative forage value and relative forage quality.

Forage rape FFY and DFY were positively correlated with the ADF and NDF contents (P>0.05, Table 7), but negatively correlated with the forage quality traits including crude protein, fat and total digestible nutrient content, and silage quality indexes including milk productivity, relative forage value and relative forage quality (P>0.05), which indicated that with the increasing of rape forage yield, the fiber (ADF and NDF) content were increasing, and so resulted silage quality reduction. The post-winter density of rape was significantly negatively correlated with crude protein contents and total fatty acids, which indicated forage rape silage quality were decreased by crude protein and total fatty acids contents decreasing with plant density increasing. The forage rape plant height had a significant negative correlation with crude protein and total fatty acid contents, and a significant positive correlation with ADF and NDF contents, which meant that forage rape silage quality were decreased by crude protein and total fatty acid contents decreasing and fiber content increasing because of the forage rape higher plant height.

The correlation analysis showed that (Table 8), the crude protein, fat, and total fatty acid contents of forage rape had an extremely significant negative correlation with the temperature and sunshine hours before wintering, but were extremely positively correlated with the temperature during the wintering period and after reviving, as well as the sunshine hours and rainfall during the wintering period, which indicated that the forage rape crude protein, fat and total fatty acid contents were increasing with the increasing of temperature in the late growth duration.

The daily maximum temperature, growth degree days, sunshine hours, and rainfall during the wintering period played significant negative roles on forage rape ADF content, and only the daily maximum temperature and rainfall during the wintering period had significant negative effects on NDF content, and that means forage rape fiber content increased with the average daily maximum temperature, sunshine hours, and rainfall were decreased during the wintering period. There was no significant correlation between lignin, starch, ash contents and total digestible nutrients, and meteorological factors during the rape growing season. The meteorological factors before wintering did not played significant roles on milk productivity, relative forage value and relative forage quality of forage rape, however, the temperature, sunshine hours and rainfall during wintering played a significantly positive roles on the milk productivity, while the relative forage value and relative forage quality were only positively correlated with the daily maximum temperature and rainfall. It indicated that the forage rape silage quality was increased with the average daily maximum temperature and rainfall increasing, the sunshine hours prolonging during wintering period.

Discussion

Forage rape was a high-quality green silage resources due to the simple planting technology, fast growth rate, high fresh forage yield and good feeding effect. Forage rape sowing in the North China Plain in autumn had a water saving and ecological conservation functions during winter［17-18］. Sowing date could regulate the rape light and temperature resources use efficiency. The total growth days were shortened by sowing date delayed, while the rapeseed yield, crude fat, fiber and crude ash contents were decreased, and the protein content increased, as well［3］. Properly sowing early can significantly increase the rape fresh biomass［19］ and improve the quality rape［20］. Liu et al.［21］ showed that higher plant density resulted to a yield reduction, because of the stalks were slender and premature senescence. The results of this study showed that the forage rape wintering rate and population density after wintering were significantly positively correlated with the temperature and sunshine hours before winter, indicating that both the temperature increasing and sunshine hours extension could significantly increase the forage rape wintering rate, and lower temperature and shorter sunshine hours during the wintering period led to a lower wintering rate and a significant reduction in the population density after reviving. In this study, compared to B. napus L., the B. campestris L. growth duration was shortened by 10-15 d, the wintering rate increased by 50.6% and the density after reviving increased by 41.5%, and the plant height significantly higher by 30.8%. The TY12 fresh forage yield and dry forage yield were the highest, which were 44.5 and 6.5 Mg/hm2, respectively. And HYZ158 and HYZ62 had lowest fresh forage yield and dry forage yield, which were 18.88 and 2.89 Mg/hm2, and 31.13 and 4.4 mg/hm2, respectively, because of the lowest after reviving were 38 890 and 441 700 plants/hm2, respectively, due to the lower wintering rate. The results of this study showed that during forage rape yield (fresh forage yield and dry forage yield) formation, the light and heat resources before wintering had a positive effect on yield, which might be due to that higher temperature and longer solar radiation time before winter could promoted the sugar accumulation in rape before wintering, and which guaranteed rape physiological function requirements during the wintering period, as well as, could improved the rape wintering rate and density after reviving, thereby increasing the yield. The lower the temperature in the wintering period and the shorter the sunshine hours, the greater the damage to rape, which led to lower wintering rate and density of rape after reviving, resulting in a reduction in the forage yield of rape. After wintering, with the heat resources and rainfall increased, and sunshine hours prolonged, resulting to lower plant height, which further led to a decrease in rape yield. It means that, the forage rape silage yield was negatively correlated with light, temperature and water resources after reviving. Therefore, it is necessary to improve the forage rape temperature resistance during the wintering period and after reviving, and increase the wintering rate and plant height through chemical control and other cultivation measures, so as to increase the density after reviving and reach higher silage yield in the North China Plain.

Sowing earlier could improve forage rape silage quality by prolong the growth period and increase nutrient accumulation［9］. Forage rape yield and silage quality were determined by clipping stage［23］, and which clipped at flowering stage were the highest for the crude protein and crude fat contents of rape cut in the initial, while clipped after the flowering stage feeding quality decreased due to the crude fiber content increased in rape stalks［13］. The results of this study showed that, compared to the B. campestris L. varieties, the B. napus L. varieties had significantly higher in the crude protein, fat, ash and total fatty acid contents, and lower in acid detergent fiber and neutral detergent fiber contents, and so milk productivity, relative forage value and relative forage quality of the B. napus L. varieties were significantly higher than that of the B. campestris L. varieties, thus  the B. napus L. varieties silage quality were significantly better than the B. campestris L. varieties. The crude protein, fat, and total fatty acid contents of forage rape had an extremely significant negative correlation with the temperature and sunshine hours before wintering, and an extremely significant positive correlation with the temperature after the wintering period and after reviving and the sunshine hours during the wintering period, indicating that the forage rape crude protein, fat and total fatty acid contents could increasing with the increasing of temperature during the late growth stage. The acid detergent fiber and content had an extremely significant negative correlation with the daily maximum temperature, growth degree days, sunshine hours, and rainfall during the wintering period, while the neutral detergent fiber content only had an extremely significant negative correlation with the daily maximum temperature and rainfall during the wintering period, indicating that forage rape fiber content were increased with average daily maximum temperature and rainfall decreased, and sunshine hours shortened during the wintering period. The content of lignin, starch, ash and total digestible nutrients had no correlation with meteorological factors in the growing season of rape. There were no significant correlationship between forage rape milk productivity, relative forage value and relative forage quality, and the meteorological factors before the wintering period and after reviving. Milk productivity had an extremely significant positive correlation with the temperature, sunshine hours and rainfall during the wintering period, while relative forage value and relative forage quality were only extremely positively correlated with the maximum daily temperature and rainfall, which indicated forage rape silage quality were optimized by the higher average daily maximum temperature, the longer sunshine hours and the more rainfall during the wintering period. The results of this study showed that rape forage yield (fresh forage yield and dry forage yield) was positively correlated with fiber content (acid detergent fiber and neutral detergent fiber) (P>0.05), but negatively correlated with the silage quality traits including crude protein, fat and total digestible nutrient contents and the forage quality indexes including milk productivity, relative forage value and relative forage quality (P>0.05), and which indicating that by the increasing of rape forage yield and fiber content, the forage rape were worse in the animals palatability and silage quality. Therefore, in the process of increasing the rape forage yield, it is necessary to synergistically reduce the fiber content and improve the silage quality by adjusting the density, harvesting date and other cultivation measures, so as to achieve the goal of high quality in the process of increasing forage yield.

In summary, the B. campestris L. type can be selected to improve the wintering rate and the B. napus L. type should be the main choice to improve the forage rape silage quality, and so considering the forage rape wintering rate and silage quality, the B. napus L. variety as HYZ62 can be selected for autumn sowing rape in the North China Plain.

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