Rational Application Methods and Precautions for Using Biogas Slurry and Biogas Residue Fertilizer on Mandarin Oranges
The peel of the sugar mandarin is orange-yellow and glossy, thin and easy to peel, covered with small sandy dots and somewhat rough to the touch. The fruit is oblate with a protruding knob at the top and a sunken stem-end navel. The flesh is reddish and bright, without white membrane, crisp and juicy, tasting refreshingly sweet with few seeds. The sugar mandarin, also known as the October orange, originated in the Qingxin, Guangning and Sihui area. Its main producing areas include Qingxin, Sihui, Guangning, Yunfu, Deqing, Nansheng Town, Yingde, Fogang and Yunan, and it is one of the main citrus varieties cultivated locally. It is named for its sweetness, which is like granulated sugar. The most authentic sugar mandarins are those produced in Huangtian Town of Sihui City and Guantian Village of Heyun Town in Qingxin County of Qingyuan City; only these are fresh and extremely sweet, with no residue and a delicate texture, truly the finest! Locally they are called rock-sugar oranges.
The biogas slurry and biogas residue produced after anaerobic fermentation in a biogas digester are an excellent biological organic fertilizer, sterile, non-toxic and highly effective. When applied to fruit trees, they can improve quality and increase yield. The following technical suggestions are offered on how to rationally use biogas fertilizer.
Choosing the application method of biogas fertilizer
In citrus orchards, biogas fertilizer is mainly applied as biogas residue used as a base fertilizer in winter and as a fruit-swelling fertilizer in summer. Biogas slurry is used as a root-zone top dressing and as a foliar fertilizer.
Rational use of biogas fertilizer according to the phenological stages of citrus trees
1. From after fruit harvest to before bud break, in order to promote normal growth of the trees, ensure the leaves overwinter safely and ensure a bumper crop the following year, spray 1-2 times as a foliar fertilizer with 0.3% urea plus 50% biogas slurry plus 10 mg/kg of 2,4-D (1 g diluted in 100 kg of water). Dig pits below the drip line of the trees and, according to tree size, apply 10-50 kg of decomposed biogas residue fertilizer plus 0.5-3 kg of calcium-magnesium phosphate fertilizer plus 0.5-5 kg of bran fertilizer to the roots.
2. For promoting new shoots. When the buds of each flush of spring, summer and autumn shoots grow to the size of a mung bean and before the shoot leaves unfold and turn green, apply an appropriate amount of decomposed bran water plus 5-50 kg of pure biogas slurry as a root-zone fertilizer, once every 15 days, for 3 consecutive applications. Spraying 2-3 times with 0.2% urea plus 50% biogas slurry together with insecticide and disease prevention can clearly promote shoots, strengthen shoots, and prevent insects and disease.
3. For protecting flowers and fruits. From bud stage to before flowering, in order to improve flower quality, apply 1-2 root applications of pure biogas slurry plus bran water fertilizer. Spray the foliage twice with 30% biogas slurry plus 0.2% borax plus 0.1% Lühwang No. 1. From after petal fall to before the end of physiological fruit drop, apply 2-3 root applications of pure biogas slurry plus bran water fertilizer, and spray the foliage 2-3 times with 30% biogas slurry plus 0.2% urea or plus 0.1% Lühwang No. 2, which can significantly increase the fruit-setting rate and raise yield.
4. During the fruit expansion stage, as with the pre-sprouting fertilization, apply biogas residue fertilizer to the roots once, and spray repeatedly with 50% biogas slurry fertilizer plus 0.3% monopotassium phosphate, which can effectively promote fruit expansion, increase sugar content, promote bright coloration of the fruit and advance ripening.
Precautions for using biogas fertilizer
1. Biogas residue is best composted with calcium-magnesium phosphate fertilizer and turf mud in a ratio of 10:1:10 plus an appropriate amount of bran fertilizer for 30-50 days, and used as a base fertilizer and fruit-swelling fertilizer.
2. When biogas slurry fertilizer is used as a foliar fertilizer mixed with pesticides for pest and disease control, a high concentration must not be used; 30%-50% is suitable. Spraying is best done before 11 a.m. and after 3 p.m. on sunny days.
3. Biogas fertilizer must not be mixed with strongly alkaline substances, pesticides, etc., so as to avoid reducing fertilizer efficiency.