Improving the Effect of Phosphorus Application on Newly Reclaimed Red Soil Fields and the Feasibility of High-Rate Phosphorus Application on Phosphorus-Deficient Soils

Newly reclaimed red soil fields have a low total phosphorus content (generally below 0.4 g/kg) and high iron and aluminum contents. The phosphorus in the soil exists mainly as iron and aluminum phosphate compounds, which are not easily absorbed and utilized by crops. Therefore, when planting crops and economic forest trees in newly reclaimed red soil fields, emphasis should be placed on increasing phosphorus fertilizer application. So, how should we improve the effect of phosphorus fertilizer application in newly reclaimed red soil fields? Is it feasible to adopt high-rate phosphorus application on phosphorus-deficient soils in our country? Experiments have proven that the following application techniques are effective:

(1) In view of the characteristic that phosphorus moves relatively slowly in soil, adopting methods such as seed dressing with calcium magnesium phosphate fertilizer and root dipping, and applying it concentratedly as a base fertilizer, gives better results;

(2) In order to reduce phosphorus fixation by red soil, emphasize mixing phosphorus fertilizer with organic fertilizer, or making it into granular fertilizer, or applying it as a foliar spray;

(3) Apply an appropriate amount of lime to reduce the fixation of phosphorus by active iron and aluminum in the soil and improve the fertilizer efficiency of phosphorus fertilizer;

(4) The application rate of calcium magnesium phosphate fertilizer is generally more economical at about 30 kg per 667 m². 

Appendix: Is it feasible to adopt high-rate phosphorus application on phosphorus-deficient soils in our country?

High-rate phosphorus application means applying in a single concentrated dose the phosphorus fertilizer that would be used over several years, in order to supply crops with phosphorus nutrition. Although this fertilization method can save labor, it also has the following drawbacks:

(1) Yield decreases and phosphorus fertilizer use efficiency declines. According to experiments by the Institute of Soil and Fertilizer of the Chinese Academy of Agricultural Sciences (1979-1985), for the cumulative yield increase of wheat over 7 years, taking annual application as 100%, one-time application over 6 years was only 77%-79%; for the cumulative phosphorus fertilizer use efficiency over 7 years, annual application was 22.4%-23.4% higher than one-time phosphorus application;

(2) Applying too much phosphorus at one time can easily induce zinc deficiency, iron deficiency, etc. in crops;

(3) A single large-dose phosphorus application causes the order of effectiveness from high to low to be: low-hill red lateritic soil > sandy field > black muddy field.

In order to improve the effect of potassium magnesium fertilizer, two points need attention during application:

(1) Since potassium magnesium fertilizer contains 30% table salt, do not use it on saline soil or on crops sensitive to chlorine such as tobacco;

(2) Potassium magnesium fertilizer is a fertilizer mainly containing potassium and magnesium, and only on the basis of applying nitrogen and phosphorus fertilizers can it produce a relatively large yield-increasing effect. The general application rate is preferably 15-25 kg per 667 m².