The Balanced Fertilization Of Peanut In The Sloping Red Soil Upland Of Southern China

Peanut is one of the main economic crops in red soil area, southern part of China. Inrecent years, nodule biomass and biological nitrogen fixation of peanut reducedsignificantly (some even to disappear), the reason for which is overuse nitrogen fertilizer inpeanut field. Overuse of nitrogen not only led to lower nitrogen use efficiency, but alsocaused a series of environmental problems like non-point pollution source from farmland.Therefore, how to cut down the application rate of chemical N by the way of promotingbiological nitrogen fixing of peanut is becoming a key issue to be solved.A field experiment was carried out on typical red soil upland, which was aimed tostudy the responses of nodule biomass, biological nitrogen fixation, root morphologicalproperties, plant biomass, SPAD value and nitrogen use efficiency under different levels ofchemical N application. Two separated peanut fields were found to serve as comparison forabove experiment. The first field is of higher indigenous N supply with a cropping systemof summer peanut-winter vegetable and the second is of lower indigenous N supply with acropping system of summer peanut-winter follow. Meanwhile, additional experiments wereconducted to see how nitragin fertilizer and microelement B, Mo will affect nodule biomass,root morphology and plant biomass of peanut.The results are as follows:1). In the first feild, biological nitrogen fixation was influenced by the levels ofchemical nitrogen application. Special acetylene reduction was negatively correlated to theapplication rate of chemical nitrogen (R²=0.88^**,p=0.005). Nodule dry matter and nodulenumber per plant decreased when higher levels of nitrogen were applied. In the secondfield, biological nitrogen fixation was promoted when very low level of nitrogen wasapplied. However, it decreased significantly when a certain level N was added.2). Root morphological properties responded sensitively to the applied N level. In thefirst field, the analyses of root morphology showed that the properties, including Total Length (TL) and Total Surface Area (TSA) and Total Forks Number (TFN) and Total TipsNumber (TIN), decreased significantly when a higher level of nitrogen was applied. But inthe second field, morphological properties were promoted when a low level of N wasapplied, but they would decrease under higher levels of N condition.3). In the first field, application of N contributed little in promoting peanut yield,above-ground biomass and total biomass (p=0.091). In the second field, very low level of Nwas needed in maintaining peanut yield. Overuse of N seemed to reduce peanut yield.4). Nitrogen use efficiency showed similar trends in both fields. Nitrogen recoveryefficiency (RE) and Agronomic efficiency (AE) showed a negative trend to the amount ofapplied N. Internal efficiency (IE) and harvest index (HI) did not respond significantly tothe amount of applied N.5). In the second field, results of N¹⁵ fertilizer tracer contents showed that theproportion of absorbed N from fertilizer were varying from 23.99% to 38.37%, which wasnegatively correlated to chemical N application rate. Biological fixed N by peanut wasvarying from 52.58 to 30.64 kg ha^-1. Biological nitrogen fixation rate was promoted when alow level of nitrogen was applied. However, it decreased significantly when a certain levelof N was added. The amount of absorbed N from soil was about 46.37 kg ha^-1, nosignificant differences were found between fertilizer treatments.6). Application of nitragin fertilizer did not significantly improve the properties suchas nodule biomass, Nitrogenase activity, root morphology, plant biomass and yield ofpeanut.7). Combination of microelement fertilizers (boron and molybdenum) promoted thenumbers and biomass of root nodules, which contributed positively the yield of peanuts andsome other economic indices. No significant differences were found when singlemicroelement fertilizer was applied or not.