Plant and Soil 261: 55–60, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 55 Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China Xiaobing Liu 1,3 , S. J. Herbert 2 , Jian Jin 1 , Qiuying Zhang 1 & Guanghua Wang 1 1 Northeast Institute of Geography and Agro-ecology, Chinese Academy of Sciences, Harbin, 150040, PR China. 2 Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003, USA. 3 Corresponding author ∗ Received 26 November 2002. Accepted in revised form 27 June 2003 Key words: crops, irrigation, manure, photosynthetic rates, quality, yield Abstract Soil nutrients and water have long been recognized as the main determining factors influencing agricultural pro- ductivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum pho- tosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation. Introduction In farmland ecosystem, water and nutrients, and their interactions, commonly impact crop growth and yield (Wang et al., 1995). Climate, soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture (Boyer, 1982; Fischer and Turner, 1978; Novoa and Loomis, 1981). Among these factors men- tioned above, water and nutrients are not only the ∗ FAX No: +1-413-545-0260. E-mail: xiaobing@pssci.umass.edu principal factors, but also can be managed easily to some extent by human activities through fertilization and irrigation. Yield of a grain crop is a function of the production of assimilates by photosynthesis, translocation of assimilates to reproductive sinks, and utilization of the assimilates by the developing seed to produce the storage materials that give the seed its economic value (Liu and Herbert, 2000). Crop photosynthesis is affected by the status of water and fertilizer levels in soil. Both stomata opening and leaf photosynthesis are inhibited when water deficit oc-