Rice straw incorporated just before soil flooding increases acetic acid formation and decreases available nitrogen

Abstract

Incorporation of rice straw into the soil just before flooding for water-seeded rice can immobilize mineral nitrogen (N) and lead to the production of acetic acid harmful to the rice seedlings, which negatively affects grain yield. This study aimed to evaluate the formation of organic acids and variation in pH and to quantify the mineral N concentration in the soil as a function of different times of incorporation of rice straw or of ashes from burning the straw before flooding. The experiment was carried out in a greenhouse using an Inceptisol (Typic Haplaquept) soil. The treatments were as follows: control (no straw or ash); incorporation of ashes from previous straw burning; rice straw incorporated to drained soil 60 days before flooding; straw incorporated 30 days before flooding; straw incorporated 15 days before flooding and straw incorporated on the day of flooding. Experimental units were plastic buckets with 6.0 kg of soil. The buckets remained flooded throughout the trial period without rice plants. Soil samples were collected every seven days, beginning one day before flooding until the 13th week of flooding for determination of mineral N- ammonium (NH4+) and nitrate (NO3-). Soil solution pH and concentration of organic acids (acetic, propionic and butyric) were determined. All NO3- there was before flooding was lost in approximately two weeks of flooding, in all treatments. There was sigmoidal behavior for NH4+ formation in all treatments, i.e., ammonium ion concentration began to rise shortly after soil flooding, slightly decreased and then went up again. On the 91st day of flooding, the NH4+ concentrations in soil was 56 mg kg-1 in the control treatment, 72 mg kg-1 for the 60-day treatment, 73 mg kg-1 for the 30-day treatment and 53 mg kg-1 for the ash incorporation treatment. These ammonium concentrations correspond to 84, 108, 110 and 80 kg ha-1 of N-NH4+, respectively. When the straw was incorporated on the day of flooding or 15 days before, the concentration of N-NH4+ in the soil was 28 and 54 mg kg-1, equivalent to an accumulation of 42 and 81 kg ha-1 of N-NH4+, respectively. There was formation of acetic acid in which toxic concentrations were reached (7.2 mmol L-1) on the 15th day of flooding only for the treatment with straw incorporated on the day of flooding. The pH of the soil solution of all the treatments increased after flooding and this increase was faster in the treatments with incorporation of straw, followed by the ash treatment and then the control. After 60 days of flooding, however, the pH values were around 6.5 for all treatments, except for the control, which reached a pH of 6.3. Rice straw should be incorporated into the soil at least 30 days before flooding; otherwise, it may immobilize part of the mineral N and produce acetic acid in concentrations toxic to rice seedlings.

Nitrogen Mineralization, Forms of Acidity and Fertility Status of a Paddy Soil as Influenced by Rice Stubble Management

“…The present work was carried out with 15 cm soil column under about 70% of the water holding capacity and might have created anoxic condition at the bottom soil layer resulting in lower NO 3 -N content compared to NH 4 -N after 84 days of incubation. A decrease in NO 3 -N content of soil following flooding (Knoblauch et al, 2014), and at 90 days after incubation of rice straw compost (Latifah et al, 2018) was earlier reported.…”

Impact of rice straw management strategies on rice rhizosphere microbiomes

“…Furthermore, in flooded soils, RS decomposition may substantially increase methane emissions (El-Sobky, 2017). To mitigate this effect, it has been proposed to leave RS on the field for at least 30 days after harvest before planting the next crop, so as to facilitate decomposition under aerobic conditions (Knoblauch et al, 2014).…”

“…This treatment may favor the soil beneficial microbes, thus improving soil health (Dobermann and Fairhurst, 2002;Nie et al, 2018). However, RS incorporation may also negatively affect rice cropping, as it may hamper effective tillage which decreases seedling emergence (Knoblauch et al, 2014). Moreover, it may even foster the spread of phytopathogens to the new crop (Dobermann and Fairhurst, 2002).…”

Equipments to manage soil and irrigated rice straw for the sequential sowing of soybean in tropical floodplains1

“…The incorporation of rice straw accelerates its decomposition, and the use of soil preparation machines and equipment for soybean cultivation can incorporate the rice straw while also correcting the soil surface roughness (Sosbai 2016). However, Knoblauch et al (2014) report that the incorporation of rice straw in the soil should be carried out at least 30 days before sowing another crop in succession. This could make this operation unfeasible due to the narrow space of time before the soybean sowing.…”