Abstract: The private department has become the main contributor of R&D investment in China, with enterprises accounting for 77.5 percent of R&D spending in 2016. However, the agricultural R&D has long relied on public research institutions. In recent years, problems like unbalanced allocation of scientific and technological resources, low conversion rate of scientific research achievements and insufficient private investment in R&D have become increasingly prominent. From the experience of developed countries, private agricultural R&D usually has higher efficiency and transformation rate of the science and technology achievements, and can also make up for the insufficient of public sector R&D investment. Therefore, encouraging private department`s participation and improving their investment have become an important way to solve the deficiency of agricultural science and technology innovation. The main reason for the lack of private R&D investment is market failure. Therefore, in order to promote private innovation, the government usually adopts measures such as tax incentives, subsidies and patent protection to make up. Theoretically, the strengthening of patent protection by the government can reduce the "free-rider" behavior, improve the private technology innovation revenue, and stimulate the private innovation motivation. Policies such as tax incentives and innovation subsidies can reduce private R&D costs and risks, and can also guide private R&D direction. In fact, the academic study of the policy’s actual effect has not yet to reach consensus, and the existing research mainly focuses on the overall policy effect regardless of the specific industries. Research in area of agricultural R&D which is in urgent need of the introduction of private participation is even less, so it`s not conducive for the formulation and improvement of specific government policies.In order to further test the effect of current incentive policies on private innovation in the field of agricultural R&D, this paper studied the impact of patent protection and additional tax deduction policies on R&D investment of agricultural enterprises. The data were selected from 77 listed agricultural, forestry, animal husbandry and fishery enterprises from 2005 to 2015.We assume that patent protection could encourage companies to invest more in R&D, and increase the intensity of R&D investment. Similarly, Tax incentives could encourage companies to invest more in R&D, and increase the intensity of R&D investment. Patent protection policy and preferential subsidy policy promote technological innovation of enterprises from the aspects of relieving market failure, protecting innovation benefits and reducing innovation costs. In the decision-making process, enterprises tend to increase R&D investment when the expected innovation income of enterprises increase with the strengthening of patent protection. At the same time, the implementation of preferential subsidy policies will further reduce the cost of enterprise R&D investment, relieve capital pressure and financing constraints of enterprises. Absolutely, the innovation behavior of enterprises is also constrained by their own capabilities.We use a multiple regression model to analysis the panel data from enterprises. The results show that the additional tax deduction policy can significantly increase the amount and intensity of R&D investment, but the promotion effect of patent protection policy on enterprise R&D is not obvious. The empirical analysis results show that enterprises reduced the intensity of R&D investment when they were facing with strong patent protection. The conclusion of empirical analysis in this paper is basically consistent with some existing research findings. Limited by the lack of research materials and shortage of knowledge, this paper only made a preliminary exploration of the effects of the two existing policies in the field of agriculture. In the future research, we hope to obtain more comprehensive data for more in-depth research and disclosure.Based on the above research conclusions, we come up with the following suggestions. Firstly, we should increase the scope and intensity of the additional tax deductions policy for R&D expenses so as to strengthen incentives for private R&D investment. Even though some researches show that the policy can promote the R&D investment of enterprises, the policy coverage of agricultural enterprises is still limited. Therefore, it is suggested to increase the intensity of the policy of additional tax deduction, expand the scope of deductible and relax the restrictions on agricultural enterprises in view of the weak industries in the agricultural field. Secondly, we should improve the patent protection system, strengthen patent enforcement, and protect the rights and interests of innovators. Under the perfect patent protection system, the public sector can obtain innovative benefits through patent licensing and transfer, and drive researchers to devote energy and time, create more better research results. The private sector can not only be encouraged by innovation, but also by better public research institutions. Third, we should strengthen reform and promote the development of a national innovation system. It has become a national goal to build a technological innovation system with enterprises as the main body, market as the guidance and the combination of enterprises, universities and research institutes.

Key words: patent, tax deduction, agriculture, private, R&D investment