## 4 Discussion
Balanced fertilization of N, P, and K can improve yield and quality of curds by regulating the absorption and distribution of broccoli's main mineral nutrients, accelerating the accumulation of nutrition relevant to curd. Through the analysis of the contribution rates of N, P, and K fertilizer to yield, it was revealed that when the yield contribution rate of N, P, and tK fertilizer reached the extreme value, the application rate of the N, P, and K fertilizer of early maturing varieties was higher than that of late maturing varieties, which may be related to the short time of early maturing varieties in the field and the insufficient transformation of fertilizer into the nutrients needed by plants, that is, the utilization rate of nutrient transformation is lower, and the late maturing varieties are associated with a relatively higher efficiency. Our study showed that the K fertilization contribution to yield even had a significantly negative effect with the continuous increase of K fertilizer application on late-maturing broccoli varieties. Our results concerning K fertilization contribution to yield were basically consistent with [PERSON] et al. 's findings. [PERSON] et al. found that fertilization with K supplementation significantly increased broccoli yield over the control. Higher K concentrations applied two weeks after planting were detrimental to broccoli growth. Incidence of hollow stem increased in field tests by the application of the K fertilization with higher concentrations [33]. In the present study, according to the recommendation models of early-maturing and late-maturing varieties under yield target, the recommended amounts of fertilizers deduced by the model were different in plots with different soil nutrient levels. For early-maturing and late-maturing varieties, under the maximum yield, the maximum recommended amounts of N, P, and K compared with minimum amounts were elevated by 52.10%/54.56%, 137.55%/210.97%, and 66.25%/76.52%, respectively. Therefore, in the soil conditions of the investigated broccoli area, the effects of N and P fertilization on the yield of broccoli were the greatest among the N, P, and K fertilizers. Moreover, the difference in the fertility of P fertilizers in soil was relatively large. These speculations have been confirmed in plots and crop arrangement records. It was also proven that the former effective functions of the N, P, and K fertilizers were highly compatible with formula fertilization recommendations. [PERSON] et al. [9] and [PERSON] et al. [34] found that soil type is one of the most important factors affecting the yield and quality of cauliflower and broccoli. It is noteworthy that the recommendation model could only be used in a recommended plot with the same soil characteristics as a fertilizer effect function trial plot. This plot was planted with the same crop rotation and arrangement mode of tillage. As for a plot with different soil characteristics from the fertilizer effect function trial plot, the parameters of formula fertilization should be modified by further experiments. That is to say, there are stricter regional limitations of the formula fertilization using the fertilizer response function method. In addition, because the parametric values of AUP (N, P, and K uptake of nutrients of crops per unit of output) in Equation (4) only accorded to the previously reported values that were not obtained experimentally [8], the reliability of the model should be tested in the next experiments. This study established the recommended formula fertilization models via soil testing based on the response functions of N, P, and K fertilizers for broccoli, particularly for early-maturing and late-maturing genotypes. The N, P, and K fertilizers in different plots under yield targets were scientifically recommended by two models and soil testing results, which are of great significance to the precise formulation of fertilizers for broccoli and other vegetables. Author Contributions**: [PERSON] and [PERSON] designed and performed the experiments.