Experiment Study On The Relation Between Soil Moisture Distribution Under Drip Irrigation And Cotton Root Distribution

Drip irrigation is the partial irrigation, the limited wetting area can change the distribution of crops root system, and influence water- absorbing of root system and the growth of aerial parts ulteriorly. Therefore, the relations between soil wetting area and crops root shape are important gist to determine the rate of soil moisture of drip irrigation, but there are quite few research results in view of this question in the domestic and foreign countries. In order to explore the effect of soil wetting area on the crops root growth and its distribution, the water consumption, so as to furnish theoretic gist for determining the rate of soil moisture under drip irrigation, this article took cotton as material, controlled soil wetting area through changing dripper discharge, studied the soil moisture distribution under different dripper discharge, the effect of soil wetting area on the crops root growth and its distribution, the water consumption under both field and barrel conditions. In the field experiment, two tectorial width(100cm and 120cm)were used for forming two soil wetting area, neutron probe was used for mensurating soil moisture, cotton root distribution were obtained by using bidirectional excavating way at cotton flowering stage, belling stage and bolling opening stage.In the barrel experiment, five dripper discharges (0.5L/h,1.0L/h,1.5 L/h,2.0 L/h,2.5 L/h) were used for forming five different soil wetting area, neutron probe and MP moisture detector were used for mensurating soil moisture, cotton root architecture were obtained by washing the soil around the root, and cotton root distribution were obtained by using bidirectional excavating way at the five cotton growing stages, seeding stage, budding stage, flowering stage, belling stage and boll opening stage. The results are as follows:(1)The dripper discharge had tremendous influence to soil wetting shape and soil moisture distribution under the point source drip irrigation. When the dripper discharge was small, the soil wetting area was narrow and deep, the soil moisture content reduced quickly with the distance increasing which was apart from dripper in the horizontal direction, and there was lot moisture content in the substrate in the depth direction. And when the dripper discharge increased, the soil wetting area became wide and shallow, the soil moisture content reduced slowly with the distance increasing which was apart from dripper in the horizontal direction. And in the depth direction, the soil moist content increased under the dripper and in the shallow layer, and reduced in the deep layer.(2)In this article, the ratio, the root length density (or root weight) of some position to the total root length density (or total root weight), was used to describe cotton's root distribution, and discovered that the rules of root distribution described by the root length and root weight were different. Regarding the root length, it was vertical parabola distribution in the horizontal direction, namely the root length density reduced with the distance increasing which was apart from the cotton plant; and in the depth direction, the root length increased firstly and then reduced with soil depth increasing, namely the most centralized position of root length was not in surface, but some depth under surface. Regarding the root weight, it's also the vertical parabola distribution in the horizontal direction, namely the root weight also reduced with the distance increasing which was apart from the cotton plant; in the depth direction, the relation between root weight and soil depth was negative exponential function, namely the biggest root weight was in the surface, and decreased progressively by exponential form with soil depth increasing.(3)The growth model of cotton root and the root distribution models in the horizontal and vertical direction were established. The increasing process of cotton root biomass could use Gaussian Model to simulate in the entire growing period. With soil wetting area becoming wide and shallow from narrow and deep, the attenuating speed quickened after entering into boll opening stage. In the horizontal direction, the root length distribution model was vertical quadratic parabola mode, and the root distribution curve tended to be smooth along with the soil wetting area broadening. In the depth direction, the model established by root length could be described by the equationy=a+b/Z+c/Z,but the model established by root weight was soil depth's negative exponential function.(4)The soil wetting area had big effect on the cotton root architecture and root distribution. When the soil wetting area was wide and shallow, the angles between taproot and lateral root were bigger, and cotton root architecture expanded widely, but the root was shallow, a large number of roots distributed in the shallow soil, and there were fewer roots in the deep soil. When the soil wetting area became narrow and deep, the angles between taproot and lateral root minished, and the root architecture became compact. But the root grown to the deep soil, there were large numbers of root in the deep soil, and the most centralized position of root moved to deeper soil. There were uniformity between cotton root distribution and spatial distribution of soil moisture.(5)Under drip irrigation, the water consumption depth of cotton root was shallow, and its main depth was in 60cm. Also, the cotton root distribution had very prodigious effect on the water consumption. When the cotton root was shallow, its water consumption depth was also shallow, and when the cotton root was deep, its water consumption depth was also deep. Moreover, the water consumption was big in the soil layer, where there were many root, and there were less water consumption when the soil layer had few root.(6) Soil wetting area had no obvious effect on total water rate of cotton in the entire soil layer. But according to promoting its root growth and ensuring its yield, we need to control soil wetting area as narrow and deep at the seeding and budding stage, and control it as wide and shallow at the flowering and bell stage.