Effects Of Different Measures Of Controlling Water And Fertilizer Supply On Biological Validity And Movement Of Deep Soil Nitrate

In this study,wheat,maize were planted,water and fertilizer were input on topsoil in the plot to find the effects of different measures of controlling water and fertilizer supply on the biological validity and movement of deep soil nitrate in a typical agricultural areas of North China Plain. Different amount of irrigation on topsoil,nitrogen and phosphate fertilizer were applied in the growth of wheat and maize. The labeled ¹⁵N was injected in 110cm in wheat season. The changes of wheat and maize soil nitrate-N dynamics was studied, root growth in different water and fertilizer conditions, crops recovery of labeled ¹⁵N and residues ¹⁵N distribution in soil profiles after crop harvest to clarify the absorption features of deep soil nitrate on water and fertilizer control and nitrate accumulation in the deep soil profile in wheat-maize cropping systems,to establish more specific measures of field management and provide a theoretical basis for the future. The main conclusions were as follows:In the experiment, the topsoil water control measures on the aboveground biomass of wheat had an impact. The results showed that in the premise of saving resources ,the treatment of reduction of nitrogen phosphorus water-saving, had no reduction in biomass production, as a result of giving full play to the water and nutrient and use of roots'continued to absorb nitrogen nutrient functions.Under control conditions of nitrogen and water, the utilization of ¹⁵N for N0W1,N0W2, N150W1, N150W2 were as follows: 8.4% and 22.4%, 12.4%, 16.3% in wheat season.The corresponding utilization of maize which were planted after wheat are as follows: 5.5%, 1.5 %, 1.7%, 2.2%. Reduction of nitrogen and control water on topsoil helped to play the biological effectiveness of accumulated nitrate.When phosphorus and water were controlled, the utilization of ¹⁵N of P60, P120, P0, were 16.4%, 11.2%, 6.8% ,respectively in wheat season; while the maize as aftercrop were 2.5%, 2.2%, 1.2%.Controlling phosphorus and water on topsoil helped to play the biological effectiveness of accumulated nitrate, while they were excessive the effects would be restrained.Reasonable water and nutrient controlling in the topsoil gave full play and use of roots'continued to absorb nitrogen nutrient functions. Nitrogen-reducing and water-saving in favor of the root system went further to deep soil. The deep root of N0W2 treatment grew best in wheat season, the root length density of 80¹50cm accounted for 32.3 percent of the ones 0¹50cm. While the highest proportion was 17.1% which was root length density of 80¹50cm accounted for 0¹50cm in N0W1 treatment. Water-saving and phosphorus-controlling in the topsoil improved the roots in the middle and lower soil growing better. The root length density of P60 treatment in the range of 60¹20cm was 12.97cm/cm3. The root length density of 80¹50cm accounted for 22.8%, 26.6% of the root length density 0¹50cm in the treatments with phosphate fertilizer applied. Root distribution and crop utilization of deep-¹⁵N coordinate marker.After wheat harvest, The labeled NO3--N which was 30cm upward and 50cm downward to the labeled place moved in vertical direction, with the peak appeared in the depth of 120¹40cm where it was 30cm below the labeled place except of N0W1. ¹⁵N moved in level direction with the distance went farther away ¹⁵N content lower and ¹⁵N would be tested in the distance exceed 15cm. After the maize harvest, ¹⁵N was 90cm upward and 70 cm downward to the labeled place in vertical direction. After the wheat harvest the impact of phosphorus -controlling and water-saving, ¹⁵N was 30cm upward and 50cm downward to the labeled place moved in vertical direction, with the peak 30cm went down; After maize harvest , most ¹⁵N was tested in 100¹80cm and the ¹⁵N has been out of the 200cm soil layer,with cumulative peak went down 50cm.The changes of soil nitrate were impacted by nitrogen input extremely serious in different wheat and maize growing period. Water and nutrient controlling in the topsoil impacted the changes of soil nitrate weakly before winter and turning green period. Water and nutrient were to become a key factor in nitrate changes at growing period, booting period and harvest period The effect of irrigation on soil nitrate was more faint throughout maize growing season than wheat season, because of more rainfall. Little changes were happened in 3-leaf period. While the effect of irrigation on soil nitrate was evident in 10-leaf period, Large bell period and harvest period.