Zhongjun FU,Hua YANG,Shenshen JIANG,Shujun LI,Jianguo ZHAO,Zhiyun QI*

1.Chongqing Academy of Agricultural Sciences,Chongqing 401329,China;2.Qianjiang Experimental Middle School,Chongqing 409000,China

With the rapid development of animal husbandry,the requirements for feed quantity and quality have been further improved.As one of the important feed sources,silage maize has good palatability and high nutritional value,which is increasingly welcomed by breeding enterprises and farmers.Developing the production of silage maize feed has become an important way to improve the economic efficiency of animal husbandry.With the adjustment of agricultural structure,the cultivation area of silage maize increases annually[1-2].

The maximum biomass yield is the most important factor affecting silage maize production.The nutritional value of silage maize feed depends on maize variety,harvesting period,mechanical operation and fermentation process.Appropriate harvesting period of silage maize is a necessary prerequisite to obtaining high-quality silage feed[3].In this study,the effects of different harvesting dates on yield and quality of silage maize were investigated in Chongqing Municipality to analyze the variation pattern of yield and quality of silage maize with different harvesting dates,aiming at providing reference for high quality,high yield,high efficiency production and rational utilization of silage maize.

Materials and Methods

Materials

Silage maize cultivar Yuqingyu 3 bred by Maize Research Institute,Chongqing Academy of Agricultural Sciences was used as the experimental material,which was planted in Ba’nan Experimental Base of Chongqing Academy of Agricultural Sciences in 2012.

Field design and management

A randomized block design was performed with three replications in five rows.Each row was 4 m in length;the area of each plot was 20 m2;the planting density was 60 000 plants/hm2.Cultivation management measures were consistent with field production.

Survey items

Maize seedlings in three middle rows of each plot were harvested at 20,27,34,41,and 48 d after pollination,respectively.Fresh weight of maize ears and straws was weight.Subsequently,the collected materials were inactivated at 105℃for 30 min and dried at 80℃to a constant weight to measure the dry weight.

Quality determination

Straw samples collected from each plot on different harvesting dates were crushed into powder using a straw disintegrator and mixed evenly.Kernel samples were collected for nondestructive detection.Main quality traits of maize kernels and straws were determined using MA.TRIX.I near-infrared diffuse reflectance spectrum analyzer (Bruker,Germany).Each sample was determined three times and the results were averaged.

Results and Analysis

Effects of harvesting date on quality of maize kernels

As shown in Table 1,four major nutritional components in maize kernels varied significantly among different harvesting dates. Specifically,crude protein and lysine contents in maize kernels were reduced with the postponement of harvesting date,which reached the maximum at 20 d after pollination (15.83% and 0.53%,respectively)and reached the minimum at 48 d after pollination(12.32% and 0.41%,respectively);crude starch content in maize kernels increased gradually with the postponement of harvesting date and the increase of kernel maturity,which reached the maximum at 48 d after pollination(67.66% );crude fat content in maize kernels increased first and then declined with the postponement of harvesting date,showing an overall descending trend.

Effects of harvesting date on quality of maize straws

As shown in Table 2,crude protein and crude fat contents in maize straws increased first and then declined with the postponement of harvesting date and showed an overall descending trend,which reached the maximum at 27 d after pollination(9.44% and 3.86%,respectively) and decreased gradually to the minimum at 48 d after pollination (6.99% and 3.33%,respectively);acid detergent fiber(ADF)and neutral detergent fiber(NDF)contents in maize straws increased gradually with the postponement of harvesting date.Yuet al.[4]found that crude protein,ADF and NDF contents in maize straws with different harvesting dates showed irregular variations,which was not consistent with the results of this study and it might be due to the different varieties or detection methods.Yuet al.[4]and Andraeet al.[5]reported that growth period significantly affected the digestibility of nutrients in silage feed.The results showed that harvesting date also posed certain effects on in vitro organic matter degradation rate(IVOMD).Specifically,IVOMD in maize straws reached the maximum at 20 d after pollination(55.75% )and declined constantly with the postponement of harvesting date to the minimum at 48 d after pollination(51.52% ).

Effects of harvesting date on yield of silage maize

At different growth stages,moisture and nutrient contents in silage maize are different.In general,early harvesting date leads to high fresh weight,high moisture content,high nutrient content,good palatability,low dry mattercontentand low total amount of nutrients;late harvesting date results in high dry matter content,high total amount of nutrients,high crude fiber content,low digestible and absorbable nutrients and poor palatability.Therefore,determining an appropriate harvesting date based on various factors is the key for ensuring the coordination between yield and quality of silage maize.As shown in Table 3,fresh matter content in silage maize reached the maximum at 20 d after pollination,and fresh weight per plant reached 2.27 kg;with the postponement of harvesting date,fresh matter content declined gradually,and dry matter content increased continuously,which was consistent with Sunet al[3].At 48 d after pollination,fresh weightand dry weightperplant reached the minimum (1.44 kg)and the maximum(0.42 kg),respectively.

Conclusion and Discussion

At 41-48 d after pollination,silage maize exhibited high yield(dry weight),low moisture content,high acid detergent fiber content,high neutral detergent fiber content,lowin vitroorganic matterdegradation rate and poor palatability.At 20 d after pollination,silage maize exhibited low dry matter content.At 27-34 d after pollination,silage maize exhibited high digestibility,high dry weight,high fresh weightand good nutritional quality,which could be used as the appropriate harvesting period for silage feed.Panet al.[6]found that silage maize should be harvested from milk stage to dough stage.However,in Chongqing Municipality and other southwest regions,maize encounters the stress of high temperature and drought during hot summer days at the late growth stage,and silage maize could be harvested in advance appropriately.

Table 1 Effects of harvesting date on quality of silage maize kernels

Table 2 Effects of harvesting date on quality of silage maize straws

Table 3 Effects of harvesting date on yield of silage maize

The optimal harvesting period of silage maize is affected by various factors,including maize variety,ecological conditions,climatic factors and cultivation techniques.Therefore,the appropriate harvesting period is not constant.To achieve high yield,high quality,high efficiency production of silage maize,the characteristics of maize variety,local fertilizer and water conditions and effective accumulated temperature should be considered comprehensively.

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