The Spatiotemporal Coupling Of Soil Water And Available Nutrients In Arid Land

Soil water and nutrients are two focuses in soil science, and the domestic and international scholars have already obtained good research findings in this aspect. But there still are urgent questions remained to be resolved. We pay more attention to soil total nutrients and soil nutrients in surface layer at preplanning than to consider region soil moisture annual variation characters. Based on production practice and soil moisture we made a research on the theory of "exactly time and exactly space" in order to realize soil water and soil nutrients in coordination of arid land.As an important index of soil fertility and soil quality, soil valid nutrients have significant correlation with crop yields and are taken as main diagnostic indexes to soil fertility and the availability soil latent nutrients, so soil valid nutrients represent nature factors,soil characters,soil management level and using condition. As the most active elements in the soil, soil valid nutrients' spatial movements have an important role in nutrient coordination and soil nutrients dislocation distribution. Based on the dynamic variation characters of active nutrients in soils, the experiment was carried out to analyze their basic relation to soil water and reveal arid land soil water spatiotemporal coupled mechanism to offer scientific basis for arid land soil water and fertility management.Based on the above objectives, this study in the first Highland of dry farmland in Guangzhong set up location observation points to monitor the variation process of water and nutrients of 0～100cm soil layers in winter wheat and maize growing period under the management of conventional fertilization conditions, and revealed the spatiotemporal variation of soil nutrients and water in the modern intensive farming and the production mode. The major conclusions show as follows:1. Relatively speaking NO3-N is the most active in soil nutrients; its movement in soil profiles is to achieve nature coordination in soil nitrogen and water.There was a clear spatial gradient distribution from the surface to the bottom of the contents of NO₃-N during wheat growth period in arid land, it showed from 0～30 cm layer of 40 mg/kg to around 70cm layer of 10mg/kg, and that below 70cm layers reduced to less than 5 mg/kg. Especially for a long time the contents of NO₃-N in the soils were the peak of 40mg/kg around of 30～40 cm layer, not in the better ventilation and oxidation condition of the surface. Relative stability of Soil moisture in 30～40cm layer was the main reason.The contents of NO₃-N during wheat growth period had obvious phase characteristics. The first 90 days of NO₃-N transported downward, and transported front promoted from about 60 cm to 80 cm layer. The contents of NO₃-N of 0-80cm layers during 90 to 120 days was depleted obviously, and that of 0～30 cm layer during 150 to 120 days soil were still in the consumption period, and that increased at 40～80 cm layers of the soil. The contents of NO₃-N of 0⁴0cm layers during 150 to 180 days recovered increasing, and the contents of NO₃-N below 0⁴0cm layers were in stability. The contents of NO₃-N after 180 days transported downward for wheat harvest period.The variation of the contents of NO₃-N in the first 30 days during maize growth period was similar to that during wheat growth period. The contents of NO₃-N of 0-100cm layers after 30 days was depleted obviously, and that of the lower layers recovered the level at preplanning. The NO₃-N leached was absorbed by maize, and this realized maturely the coordination in soil water and nutrients.2. The clear spatial gradient distribution of the contents of available N in the soil profiles in arid land corroboratesd modern fertilization system, the spatiotemporal variation of the contents of available N presented "two elements structure characters", that was the contents of available N above 40cm layers was stable,the contents of available N below 40cm layers increased at first and then decreased,the contents of available N in deep soil layers during the middle and latter growth period of wheat was depleted significantly. The variation of the contents of available N in upper soil layers was little.The variation of the contents of available N in 0～20cm layers during maize growth period was little. The contents of available N in 20～70cm layers in the first 30 days of maize growth period was decreased significantly, for maize roots distribute relatively shallow. Available N after 30 days of maize growth period was in stability.3. Reduction of the vertical gradient of available P in soil profiles Soil was more significant. The contents of available P in 0～60cm layers during the wheat period were from 13mg/kg in the surface to 5mg/kg and it decreased with wheat period simultaneously. This confirmed the use of phosphate fertilizer, also reflected biological availability of P in the deep soil layers. Especially in the latter period the contents of available P below 60cm in the deep layers were depleted significantly, this confirmed the extension of the process of roots in arid land.The overall level of available P in the soil profiles in the growth stage of maize was low; the variation in the soil profiles was in the 9 mg/kg and 3mg/kg. However, soil phosphorus still represented obviously distribution of gradient. The contents of available P in 0～100cm layers during the maize period were at very low level, the variation in the soil profiles from top to bottom was in the 5mg/kg and 3mg/kg. The contents of available P above 40cm layers increased gradually along with maize growth period during 60th to 70th day of growth period. Increment of soil available P had a closely relationship to that of soil water. The soil P was depleted from 75th day of the growth period. Despite the relatively shallow root distribution of maize, P in deep soil has equally important biological significance.4. Soil available potassium mostly change along with the time was more obvious than along with the spatial in wheat growth period,because soil parent material type affected soil available potassium more strong than human culture fertilizer effect. Soil available potassium depletion was above 50cm soil layers in wheat growth earlier period, the depletion of soil available potassium under 50cm layers from 100 to 170 days was very obvious,the decrement of soil available potassium was an average of 50～55mg/kg in wheat growth period in each soil layer.The distribution characteristics of soil available potassium was the clear time gradient distribution in the soil profiles in maize growth period,and there was the lowest value in 40～70cm layers. The variationg of the contents of soil available potassium in 0～30cm layers was little,but the variationg of the contents of soil available potassium in 40～70cm layers was obvious,especially the decrease of the contents of soil available potassium under 40cm layers in maize growth later period was very obvious.5. Except 0～20cm soil layers in soil profil in arid land in Guanzhong,the moving characteristics of moisture in other soil layers was violent,that was the variation of soil moisture in the range of 20～100cm was synchronous. But the variation of the contents of soil moisture in 0～20cm soil layers was strong,that was the safety and guarantee of plant growth was low. And the change of the contents of soil moisture under 20cm soil layers was little,maintained above 50～80% of soil field capacity. And because of the strong moving ability of soil,it basically ensured plant to avoid water stress. The variation characteristics of soil moisture determined that the variation of surface soil moisture in arid land was little,so the content of soil available nutrient in deep soil layers was more important.