What kind of soil standards do high-yield rice require?

(1) Distinct profile horizons, deep plough layer, good texture. For high-yield rice, a plough layer depth of about 20 cm is best. The plough layer should be fertile, thick and soft, with a high aggregate content, good structure and aeration, and suitable tillage properties. If the plough layer is too shallow, rice roots develop poorly; if too deep, floating mud forms easily, which is unfavourable for rice rooting and early growth. The texture should be moderate, neither too sandy nor too clayey: when dry-ploughed, the plough does not turn up large clods and the soil breaks up easily under harrowing; when wet-ploughed, it does not settle into a hard pan; when drained and dried, it does not crack widely, and the cracks close up easily after re-flooding.

(2) High organic matter content, with sufficient and balanced nutrients. High-yield paddy fields generally require an organic matter content of 2-4%, a total nitrogen content of 0.13%-0.23%, of which hydrolytic fluorine accounts for 5-10% of total nitrogen, a total phosphorus content above 0.1% (available phosphorus above 5 kg per mu, or about 13-70 ppm), and a total potassium content above 1.5% (available potassium above 0.5 kg per mu, or more than 8-10 mg of potassium per gram of soil). At the same time, a relatively high cation exchange capacity (not less than 20 milliequivalents per 100 g of soil) and a relatively high base saturation (60-80%) are required; the soil pH should preferably be slightly acidic to neutral (pH 6-7.5), with sufficient major elements and no deficiency of trace elements. There should be both a large amount of active available nutrients and a large amount of inactive available nutrients, so that the various nutrient elements are supplied in a balanced way, without nutrient deficiency or loss of fertility, ensuring the normal growth and development of rice.

(3) Good water retention, fertilizer retention and fertilizer supply capacity, together with appropriate permeability. High-yield paddy fields need good water and fertilizer retention, and must not leak water or fertilizer; that is, they should both accumulate and preserve large amounts of nutrients and supply them fully and persistently. When the amount and timing of fertilizer application vary slightly, the paddy field itself has a certain regulating capacity and good buffering performance, so that premature senescence and excessive vegetative growth of the rice plants do not occur. Paddy fields should also have a certain amount of seepage, so that part of the oxygen can enter the lower soil layers with the percolating water, thereby raising the soil redox potential and reducing the accumulation of toxic substances. According to experiments, fields with a daily seepage rate of about 10 mm give higher yields. One irrigation should be retained for 5-7 days. If the seepage rate is too high, it will cause a large loss of nutrients, which is also unfavourable.

(4) Vigorous activity of beneficial microorganisms. In paddy fields with high fertility, the activity of beneficial microorganisms is more vigorous than in ordinary paddy fields, and these microorganisms play an important role in creating and regulating soil fertility. According to research, the numbers of nitrogen-fixing bacteria, nitrifying bacteria, ammonifying bacteria, aerobic cellulose-decomposing bacteria and sulphur bacteria are positively correlated with fertility. Where fertility is high, their numbers are large and the biochemical intensity (respiration intensity in mg CO2/hour per kg of soil, ammonification intensity in mg/100 g of soil) is high; that is, biochemical action is strong.