Since the southern part of China is acidic soil, and the north is alkaline alkaline calcareous soil, the method for determining effective phosphorus is different, and the standard is naturally different. The standard (mg/kg) of available phosphorus (P) in acidic soils is: 0 to 15 is low; 16 to 30 is medium; >30 is high. The standard (mg/kg) of available phosphorus (P) in calcareous soil is: <6 is low; 6-10 is medium; >10 is high. When the soil available phosphorus content is low, it indicates that the soil is deficient in phosphorus or severely deficient in phosphorus, and the application of phosphate fertilizer has obvious or extremely obvious effect; when the soil available phosphorus is medium, it indicates that the application of phosphate fertilizer has certain effect; when the soil has high effective phosphorus content At the time, it indicates that the soil is rich in phosphorus, and the effect of applying phosphate fertilizer is often not obvious. However, for high-yield fields, although the soil available phosphorus content is high, the principle of nutrient balance should also be considered, so proper application of a small amount of phosphate fertilizer is also necessary.
a:
1 The content of available phosphorus in soil is obviously affected by the application of phosphate fertilizer. With the application of a large amount of phosphate fertilizer every year, the soil available phosphorus content will gradually increase. Therefore, the amount of phosphate fertilizer should be appropriately adjusted as the soil available phosphorus content changes.
2 Practice has proved that the combined application of nitrogen and phosphorus is conducive to crop yield increase. It can be seen that it is wrong to apply only phosphate fertilizer or partial application of nitrogen fertilizer. The concept of nutrient balance should be established.
A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.
Bandpass filters are widely used in wireless transmitters and receivers. The main function of such a filter in a transmitter is to limit the bandwidth of the output signal to the band allocated for the transmission. This prevents the transmitter from interfering with other stations. In a receiver, a bandpass filter allows signals within a selected range of frequencies to be heard or decoded, while preventing signals at unwanted frequencies from getting through. Signals at frequencies outside the band which the receiver is tuned at, can either saturate or damage the receiver. Additionally they can create unwanted mixing products that fall in band and interfere with the signal of interest. Wideband receivers are particularly susceptible to such interference.[3] A bandpass filter also optimizes the signal-to-noise ratio and sensitivity of a receiver.
In both transmitting and receiving applications, well-designed bandpass filters, having the optimum bandwidth for the mode and speed of communication being used, maximize the number of signal transmitters that can exist in a system, while minimizing the interference or competition among signals.
Outside of electronics and signal processing, one example of the use of band-pass filters is in the atmospheric sciences. It is common to band-pass filter recent meteorological data with a period range of, for example, 3 to 10 days, so that only cyclones remain as fluctuations in the data fields.
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