| Agricultural production is located at farmland scale and the main research subject of agricultural drought is crop. Because of the specific of climate type and soil character, it is essential to disscuss the drought index to monitoring agricultural drought in this area.Two years experiments with summer maize as a tested material had been conducted in field. The experiments were carried out in two different fields, A and B. There were four irrigation treatments and three N rates including0,140,280kg/hm2in A field. B field consisted of three levels of irrigation coupling with three different fertilization treatments, check(CK), manure(M) and NPK. Test observation was carried out between jointing stage and tasseling stage of maize. Observation projects include canopy temperature, soil moisture, soil temperature at5cm and10cm, maize morphology, yield and weather condition during growth stage of maize. The main findings were obtained as follows:Although sometimes the precipitation happens frequently at red area in summer and autumn, the short-term drought occurs easily. We suggest that it should focus on the changes of soil surface water content as short-term drought happens. It could indicate when the air is dry and when it wet during maize growth stage as well. Using consecutive rainless days, it found mild and moderate drought had happened in experimental area during maize growth stage in2010and2011. Severe drought was monitored by crop water deficit index at that stage.When atmospheric drought happened in experimental area, soil moisture at10cm and20cm depth soil layers decreased quickly and they could dropped to40%of field capacity. On the contrary, soil moisture at30cm and40cm reduced slowly and they could remain at more than80%of field capacity.Crop water stress index (CWSI) can be used to detect water status in red soil of south China, where the climate type is subtropical monsoon. The results showed that it was not suitable to define low baseline under cloudy condition in this region, because the vapor pressure deficit (VPD) was as low as1to1.25kPa. At sunny condition, however, the regression testing effects were at0.01significant levels despite that the VPD ranged only from1to3kPa. Nitrogen fertilization had an effect on low baseline of maize. Nitrogen fertilization reduced the low baselines of maize. The low baseline decreased as the amount of nitrogen fertilization increased. CWSI is an indicator of maize crop water stress status during the short-term drought happening period.The regression testing effects are at0.01significant levels between CWSI and maize yield.The results suggest that we can use CWSI to monitoring short-term drought at farmland in red soil areas, and it can be used to estimate the final yield of maize.The temperature of soil surface at5cm depth is a good index to monitoring soil water status in farmland. The result of experiment found that the soil temperature at5cm and10cm depths in different irrigation treatments plots were not identical. Meanwhile the difference of soil temperature between different irrigation treatments at5cm depth was larger than that at10cm depth. In addition, the temperature of the different soil layers and the final crop yield had significant correlation (P<0.05), and the coefficient of determination for relationship of soil temperature at5cm depth and crop yield is greater than the coefficient between10cm soil temperature and yield. So we can conclude that the soil temperature at5cm depth could reflect the farmland soil moisture better than the soil temperature at10cm depth.The results show that the meteorological index, crop drought index and soil moisture index could reflect drought status at farmland. But they had not fully reflect the drought status in the red soil area at field scale at a variety of conditions. To monitoring crop water stress status effectively and timely, we advise that several different indices should be combined to reflect the agricultural drought in red soil area at farmland scale. |
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