改革开放以来，我国工业化和城镇化快速发展，极大地促进了农业的进步，但同时也带来了许多诸如农业基础设施薄弱、耕地退化严重、科研成果转化率不高等现实问题。近年来，随着现代科学技术成果在农业领域的广泛应用，全国各地针对退化、污损及未利用土地进行了大规模的农业工程建设，并取得了显著成效。农业工程的科学实施需要一系列工程技术为依托，而工程试验则是工程技术研发的重要手段，能够为工程实践提供理论指导和技术支撑。黄土丘陵沟壑区是我国典型的生态脆弱区，近些年实施了大规模的治沟造地土地整治工程。在该地区开展农业地理工程试验与应用研究，对于治沟造地工程的科学实施和农业持续高效发展具有重要意义。

本研究以黄土丘陵沟壑区为研究区，以农业地理工程试验为切入点，以“区域评价-农学试验-工程应用-理论探究”为主线，系统分析了区域人地关系和农业发展阶段、农业生态系统、作物与土壤关系，针对边坡-沟道整治工程中的边坡安全与防护、土体营造与熟化、作物试种与推广的理论和技术问题，在延安市工程项目区先后开展了边坡防护试验、客土改良试验、油菜种植试验和种植模式调整试验，进行了农业地理工程试验与应用研究，并构建了农业地理工程试验与应用的初步理论框架。

本研究获得的主要结论如下：

（1）不同开挖坡度和植被护坡措施下治沟造地工程边坡的综合效益、植被生长水平、坡面侵蚀状况和工程效益等指标均存在显著差异。53°开挖边坡的综合效益明显优于45°和63°边坡，而一种或多种植被群落类型的综合效益显著优于无植被覆盖的边坡。随着坡度的增加，植被平均高度、物种丰度、植被覆盖度、产流产沙量等植被生长和坡面侵蚀指数均呈显著下降趋势，而新增耕地面积、开挖土方量等工程效益指标呈上升趋势。

（2）不同覆土类型及厚度对土壤理化性质和作物产量的影响存在显著差异。随着红粘土覆土厚度的增加，土壤的黏性特征逐渐增强，土壤容重、粘粒比例、土壤紧实度、土壤含水量、土壤有机质等含量增加，而土壤总孔隙度和砂粒比例逐渐减小。玉米产量较高的样区为马兰黄土5cm、10cm，饲料油菜产量较高的样区为马兰黄土和红粘土5cm样区，马铃薯产量较高的样区为马兰黄土10cm、15cm。

（3）黄土丘陵沟壑区具备种植春季饲料油菜的自然生态适宜性，春播饲料油菜播种量以3.9-5.1kg/hm2为宜，苗期密度宜控制在22.5万株/hm2左右。在研究区进行饲料油菜推广，发挥饲料油菜生长快、产量高、投入少、饲用效果好等特点，能够有效促进当地“种植+养殖+观光”的新型农业发展模式，可为当地实现“一季变两季”、种植模式调整提供更多的优选方案。

（4）黄土丘陵沟壑区沟道土地整治后农业“一季变两季”种植模式在实践层面具有可行性，具体为“甜糯玉米+华油杂62”、“饲料玉米+华油杂62”和“延油二号+华油杂62”，其净收益分别约为亩均1350元、1580元和1324元，较传统的单季作物有显著的提高，对于提升土地利用效率和经济效益具有重要意义。

（5）农业地理工程试验的研究对象为区域农业生态系统，作物生长与土壤环境之间的相互作用是其中最为重要的关系。试验设计的关键在于，通过开展土地改良和作物优选的耦合试验，来实现作土系统的优化调控。工程试验的应用框架可分为时间-组织维、空间-对象维和时空-逻辑维三个维度，其中时间-组织维包括区域评价、试验设计、组织实施、结果分析和应用推广五个阶段；空间-对象维包括团聚体、坡面、田块、沟域、流域和区域六个尺度；时空-逻辑维包括明确问题、选择目标、系统分析、系统优化、做出决策和付诸实践六个步骤。

Since the reform and opening up, the rapid development of industrialization and urbanization in China has greatly promoted the progress of agriculture, but also brought many practical problems such as weak agricultural infrastructure, serious degradation of arable land and low conversion rate of scientific research achievements. In recent years, with the wide application of modern scientific and technological achievements in the field of agriculture, a large scale of agricultural engineering construction has been carried out across the country for degraded, polluted and unused land, and remarkable results have been achieved. The scientific implementation of agricultural engineering needs a series of engineering technology research, and engineering experiment is an important means of engineering technology research, which can provide theoretical guidance and technical support for engineering practice. The loess hilly and gully region is a typical ecologically fragile region in China. In recent years, the region has carried out a large scale of gully land consolidation, which has provided a solid foundation for the rapid transformation and modernization of agriculture. It is of great significance for the scientific implementation of gully land consolidation project and the sustainable and efficient development of agriculture to carry out research on agricultural geographical engineering experiment and application in this area.

Based on the current situation of the agricultural development and engineering construction in loess hilly and gully region, taking the hilly and gully area of the Loess Plateau as the research area, focusing on the land remediation engineering technology and the sustainable land use strategy, the study carried out the experiments of foreign-soil improvement, the slope protection and planting pattern adjustment in the Baota District of Yan'an City. These experiments explored the movement laws and interaction mechanisms of water, soil, gas, and biomass in farmland ecosystems, and proposed measures to improve the quality of farmland, increase the efficiency, and enhance the stability of the channel land. Then, based on the series of engineering tests carried out in the research area and supported by the relevant theoretical knowledge of agriculture, geography and engineering, the research framework of agricultural geographical engineering experiment and application was discussed from the aspects of concept connotation, research object, experimental principle and application framework, and applied in practice in other areas. The main conclusions of this study are as follows:

(1) There are significant differences in the comprehensive benefit to slopes, as well as the levels of vegetative growth, soil erosion and engineering benefit of the slope engineering with different excavation slopes and vegetation protection measures. The comprehensive benefit of the 53° slope was significantly better than that of 45° and 63° slopes. In addition, the comprehensive benefit of slopes with one or more vegetation styles was better than that of non-vegetation covered slopes.

(2) The effects of different soil types and thickness on soil physical and chemical properties and crop yield were significantly different.With the increase of the thickness of red clay overburden, soil viscosity gradually increased, soil bulk density, clay ratio, soil compactness, soil water content and soil organic matter increased, while total porosity and sand ratio decreased.The sample areas with higher maize yield were malan loess 5cm and 10cm, the sample areas with higher feed rape yield were malan loess 5cm and red clay 5cm, and the sample areas with higher potato yield were malan loess 10cm and 15cm.

(3) The loess hilly and gully region has the natural ecological suitability for planting rapeseed in spring. The forage rape seeding amount should be 3.9~5.1kg/hm2, and the seedling density should be controlled at about 225,000 plants /hm2. According to the versatility of forage rape, the region can develop multiple product combination modes, such as feeding, vegetable + feeding, vegetable + sightseeing + oil, etc. Scientific promotion of forage rape planting can promote the development of multi-functional agriculture that integrates "planting + breeding + processing + sightseeing".

(4) Different sowing dates had significant effects on the growth of crops. At present, the feasible farming modes of "changing from one season to two seasons" in loess hilly and gully region are "sweet glutinous corn + hua youza 62", "feed corn + hua youza 62". At the same time, through the calculation and analysis of the income and cost of the main crops planted in the sloping land, newly constructed land and two crops land, this study proposes the agricultural planting model to optimize the land use efficiency and benefit in this region, which is of great significance to the local agricultural structure adjustment and rural economic development.

(5) The agricultural geographical engineering experiment refers to a series of field test methods aimed at exploring the operational laws and impact mechanisms of various elements in the agricultural system and providing engineering parameters and countermeasures for the scientific implementation of agricultural geographical engineering. The research object is regional agroecosystem, and the interaction between crop growth and soil environment is the most important one. The key of the experiment design is to realize the optimal control of soil relationship by carrying out the coupling experiment of land improvement and crop optimization. The application framework can be divided into three dimensions: time-organization dimension, space-object dimension and spatio-temporal dimension.