## 4 Discussion
### Effects of Intercropping on System Productivity and Silage Quality
We indeed found that the ammonia-N contents in both years were increased by 7.9% on average in the mixed silage, but the differences between the two systems were not significant (\(p>0.05\); Table 4). What is more, the pH values of all treatments were lower than 4.0, which are optimal for silage preservation in a stable form [38]. In fact, alfalfa is difficult to ensile successfully not only for the relatively high buffering capacity, but also for the low WSC contents and low DM content [38], this is also one of the important reasons why we suggest interseeding corn into alfalfa during a hot-rainy summer instead of ensiling pure alfalfa. In our study, the addition of alfalfa significantly reduced the silage DM content (\(p<0.001\); Table 3), but significantly increased the WSC content by up to 68.4% compared with that of 100% corn silage control, this is inconsistent with previous studies which showed that WSC content had a linear increase as the proportion of corn increased [12; 13]. This could also be explained by that the monocultured corn was more mature than the intercropped corn when harvested, for which the DM content increased but the WSC decreased sharply owing to starch accumulation [37]. Thus, a higher WSC content, as the primary fermentation substrate, enhanced the fermentation characteristics of the alfalfa-corn mixed silage with a relatively low pH value and a higher LA content (8.5% and 38.8% higher than that of CK in 2017 and 2018, respectively) [34; 39]. [PERSON] et al. [40] also showed that the addition of the legumes resulted in the production of higher concentrations of organic acids. In spite of a slight reduction of V-score in AC compared with that in CK, the mixed silage achieved a great fermentation quality (Table 4). Intercropping and the following mixed ensilage had few effects on fiber content and RFV value (Table 2), the results agree with previous studies [13; 40]. Multicriteria Assessment on Productivity and Quality Performance of Alfalfa-Silage Corn Intercropping  
In the establishment year 2017, the productivity of alfalfa was lower than that in the following production year (\(p<0.05\); Table 2). Meanwhile, the alfalfa needed a longer growth period in spring 2017, and silage corn was planted a few days later than that in 2018. So, the corn was harvested at the one-third milkline in 2017, while at the two-third milkline in 2018. This longer growth period increased the silage DM content but reduced the silage WSC content, LA concentration, as well as the forage FM yield in 2018 (Tables 1-3) [37]. For the effect of N fertilizer, the DM yield and CP content of the intercropped corn increased significantly as the N rate increased (\(p<0.05\); Tables 1 and 2), for the reason that the addition of N fertilizer could reduce interspecific competition for N and improve N nutrition in silage corn [3; 41]. The alfalfa DM yield and CP content were affected by the N rate only in 2017 (\(p<0.01\); Tables 1 and 2), when the alfalfa was newly established and more sensitive to the N addition and the increased shading from the larger corn canopy. Corn plant density was the key factor affecting the alfalfa to silage corn ration in the mixed silage for the significantly opposite effects on alfalfa and corn yield in both years (\(p<0.05\); Tables 1 and 2). The previous paper published from the system has reported that the density of alfalfa stands decreased with the increasing of corn plant density [14], and the alfalfa yield during summer was also significantly affected by the corn plant density (Tables 1 and 2). As a result, the alfalfa proportion ratio in mixed silage based on an FM basis was influenced by the N rate, corn plant density, their interaction (Tables 1-4), and the year, the total system DM yield and CP yield were negatively related with the alfalfa proportion in the mixed silage (data not shown).