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On-farm conservation and utilization of crop landraces have been proposed as means of conserving plant germplasm, in contrast to ex situ germplasm conservation, but little is known about the effectiveness of this approach. This paper reports the findings from a survey conducted in 15 unique ethnic groups of the Yunnan Province on the conservation and utilization of paddy rice, wheat (including wheat, barley, oats, and rye) and maize landrace varieties through participatory rural appraisal (PRA) and questionnaires. The surveyed regions covered 306 villages (the village group) from 237 administrative villages in 124 towns (township) distributed in 36 counties of 11 prefectures (city) in Yunnan Province. The survey showed that 44.8%, 77.5%, and 37.3% of the visited villages had lost their paddy rice, wheat, and maize landraces, respectively. A total of 901 landraces were collected, including 371 rice, 119 wheat, and 411 maize varieties, respectively. There were 2.9 on-farm varieties on average per village, 3.3, 8.0 and 5.2 varieties on average per 100 households, 1 000 peasants and 100 Ha farmland areas, respectively. Among the 306 villages, two villages (Laomian and Qingkou) maintained the highest crop diversity with 18 varieties (including 10 rice and 8 maize varieties) and 14 paddy rice varieties. Also, on-farm varieties in different ethnic groups varied significantly from each other, ranging from 16 to 120 varieties per group. The diversity of paddy rice varieties was the highest, ranging from 1 to 72, and the diversity was mainly distributed in southern, southwest Yunnan of tropical, subtropical ethnic regions. The wheat varieties ranged from 0 to 47 and distributed in northern, northwest Yunnan of high altitude, temperature, and cold ethnic regions. The maize varieties ranged from 4 to 40. These patterns of variation in on-farm varieties are directly associated with traditional culture and custom for the ethnic minorities and reflect the lack of improved varieties for the local special environments. These findings confirm the role of on-farm conservation in plant genetic resources in China and provide baseline information for better on-farm conservation and utilization of plant germplasm in China.

Improvement of utilization rate of nitrogen fertilizer (NUR) is one of research focuses in wheat. In a two-year field experiment, the NUR of wheat variety Guangmingmai 1 in the wheat-rice rotation system in response to sowing date (S), density (D), and nitrogen application rate (N) was studied using a mathematical model based on quadratic regression rotation-orthogonal combination design. Among the three factors, nitrogen application rate had the greatest effects on NUR, followed by sowing date and density. Several S+D+N combinations resulted in high yield and high NUR under the experimental conditions. The highest yield level (6800-7200 kg ha -1 ) was obtained in the combination of S between October 28 and November 2, D between 1.6 and 1.8 million plants per hectare, and N at 200 kg ha -1 . Simultaneously, the NUR was higher than 42.0% (the maximum was 44.8%) with a credibility larger than 95%. At the yield level of 6200-7000 kg ha -1 and NUR higher than 41.0%, the optimal S, D and N were 21-27 October, 1.2-1.5 million plants per hectare and 190-225 kg ha -1 , respectively. At the yield level of 5900-7250 kg ha -1 and NUR higher than 39.0%, the agronomic practices were recommended to be S between November 3 and November 11, D be- tween 2.1 and 2.4 million plants per hectare, and N between 190 and 210 kg ha -1 .