Study on the growth rhythm and water uptake character of cotton roots in arid area oasis

在生态环境极其脆弱的我国西北干旱地区，作物的根系吸水活动不仅对土壤水分动态产生重要影响，而且强烈影响着地表水、土壤水和地下水的相互转化过程。基于对大田棉花一个生育期的试验和观测的数据，本文对干旱区绿洲棉花根系生长规律以及吸水特性的相关内容进行了理论分析和研究，并获得了以下一些成果或结论：（1）根据实测的棉花毛细根长密度数据，建立了地面漫灌棉花毛细根系生长模型。在此基础之上建立了依赖于气象要素、土壤水分要素以及棉花根长密度等要素的地面灌棉花根系吸水模型。 （2）在对基础数据进行分析的基础上，本文归纳出两种灌溉方式下棉田土壤水分动态变化的规律，并对这两种灌溉方式下土壤水分变化的规律进行了比较，其差异性主要体现在表层土壤水分的变化差异，不同生长期之间的变化差异等方面上。（3）地面灌棉田棉花根系分布集中在0-30cm层次的土壤中，根长密度最大值出现在10cm左右的土层中。从二维的角度来看，根系分布最集中的区域为10cm深度土层距离棉株15-25cm的区域，最大达40mm/cm3以上。膜下滴灌棉花根系空间及时间变化有与地面灌棉田明显不同的地方，一是根长密度最大值出现在地表附近，根长密度随深度增加呈波动的减小趋势。二是时间变化的区别也很明显，在7月11日之前，根系深度在增加，根长密度在增大。但7月11日之后，根系深度有所增加，但根长密度变化很缓慢，看不出增大的趋势也看不出减小的趋势，似乎是处在一个动态的平衡之中。（4）地面灌和膜下滴灌棉花的叶面积指数变化有一些异同点：在时间上都呈抛物线形变化，而且最大值出现的时间基本一致；膜下滴灌棉花叶面积指数总体上要大于地面灌棉田。（5）根据茎流计测定的9月份棉花实际蒸腾量资料，棉花蒸腾的日变化基本规律是，0时至9时，棉花茎流维持在一个很低的水平。10时开始，茎流开始迅速增加。至午后15时达到最大值，之后持续一段时间，茎流值开始回落。茎流日间差别不太明显，说明这一段时间棉花茎流相对比较稳定。In the arid area of the North-west China, where the ecological environment is extraordinary fragile, the action of water uptake by crop roots play an important effect not only on the dynamic of soil water, but also on the conversion process among surface water, soil water and ground water. Based on the data of a period of duration of field cotton, this paper made some theoretical analysis on the growth rhythm and water uptake character of cotton roots, and has got the following conclusions: (1) Based on the data of the cotton hair roots, this paper established the growing model of the cotton hair roots in the condition of ground irrigation. This paper also established the cotton root water uptake model, which relied on the weather condition, soil water content and cotton hair roots length density. (2) Based on the analysis of the foundational data, this paper found some different dynamic regularities of the cotton field under different irrigation systems, which representing on the different of soil water content of different layers or of different growth phases. (3) The ground irrigative cotton roots distribute concentratedly in the 0-30cm soil, the maximum of cotton hair roots length density was found in the 10cm depth soil layer. From the perspective of two-dimensional, the concentrated distributed region is in the region of 10cm depth and 15-25cm far from the cotton plant, the maximum of cotton hair roots length density can forereach 40 mm/cm3. The temporal and spatial variation of the Mulch-trickle cotton roots have obvious different from the ground irrigative cotton roots, the maximum of cotton hair roots length density was found in the surface soil, as the depth increasing, the cotton hair roots length density diminish undulatingly. The different of temporal change is obvious, too. Before Jul.11st, the depth of cotton roots is increasing; the hair roots length density is augmenting. But after Jul.11st, the depth of cotton roots increase a little, and the change of the cotton hair roots length density is very slowly, we can’t found whether it is increasing or not, it was seemed in a dynamic balance. (4) The temporal changes of LAI of the cotton under different irrigation systems have some similarities and differences: they all appeared a parabolic shape change over time, and their maximums appeared at almost the same time; As a whole, the LAI of Mulch-trickle cotton is greater than the LAI of ground irrigated cotton. (5) According to the data measured by Sap Flow Probe in Sep., the daily regular of the diurnal variation of cotton sap flow is like this: from 0 o’clock to 9 a.m., the sap flow of cotton hold on a very lower level. And from 10 a.m., it increases quickly. And on the 15 p.m., it reaches its acme, then after the state sustains for a period of time, the sap flow begin fall down. The day variance of the sap flow isn’t remarkable, which is showed that the sap flow of the cotton is steady correspondingly in this time

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