关键词: 冬小麦, 农田尺度, 晚霜冻害, 空间分区, 发育进程, 土壤肥力

Abstract: 【Objective】At the field scale, the study was conducted to investigate spatial differences of late frost injury to winter wheat and their influences on yields. The reasons for the spatial differences were discussed, which might provide a priori knowledge for predicting late frost damage and regulating influence factors.【Method】A frost-prone farmland in Shangqiu was selected as the study area where a winter wheat cultivar Aikang58 was sowed. Natural frost occurred in April 7, 10 and 21, 2013, when the winter wheat was in the periods from middle jointing to booting stage. At maturity, ear number and actual yield per square meter, and soil fertilities were respectively measured based on one hundred sampling points (the interval between samples is 5 m). Four indexes, such as dead ear rate (DER), injured ear rate (IER), injured ear index (IEI) and yield loss rate (YLR), were established to evaluate late frost damage. Their spatial differences and relations with ear number and actual yield were estimated using multiple linear stepwise regression method, geo-statistics method, cluster method, ANOVA and multiple comparison methods. In order to reveal the reasons for the spatial differences, late frost indexes related to developmental progressions of winter wheat and soil fertility factors were measured at early returning green stage. 【Result】 Through the stepwise regression, DER was found to be the only factor affected ear number and showed a negative effect. Factors, including IEI, DER and IER, all showed negative effects on actual yield. Of all the factors, IEI was the most powerful (its direct path coefficient reached -0.453) to actual yield. DER, IER and IEI were the factors impacted YLR and all showed positive effects, indicating that YLR increased with their increments. DER showed the most influence (its direct path coefficient was up to 0.626) on YLR. Late frost damage had a positive spatial autocorrelation (P＜0.05). Sampling points with similar frost damage degrees tended to the clustering distribution in the local space. Of all the damage evaluation indexes, YLR showed the strongest clustering distribution (Moran’s I=0.5538). The result of frost damage divisions indicated that ear number and actual yield significantly decreased (P＜0.05) with deepening frost injuries. The index DER showed the biggest increase (the amplitude reached 271.3%), followed by IER (36.4%) and IEI (31.8%). They comprehensively led to a sharp rise of YLR (132.1%). Sampling points with the most severe frost injury almost showed a contiguous distribution. Developmental progression of winter wheat and soil nitrogen in the turn-green stage showed obviously spatial differences and had a certain spatial correlation with late frost damage. A significant difference (P＜0.05) was found between total nitrogen, hydrolysable nitrogen, available phosphorus, available potassium and organic matter and the frost evaluation indexes. As soil nutrient content reduced, frost damage had a deepening trend. After the green up, the persistent drought made the soil water content decreased rapidly, further exacerbating the extent of frost damage. 【Conclusion】 At the field scale, the spatial differences of ear number and actual yield influenced by late frost damage were obvious. The spatial pattern of frost damage was significantly related to the developmental progress of winter wheat and soil nitrogen at returning-green stage, indicating that it maybe has an opportunity to predict frost damage risks early and regulating influence factors in the fine scale.

Key words: winter wheat, field scale, late frost damage, spatial division, developmental progress, soil fertility