Toshifumi Murakami

The Effects of Soil Conditions and Nitrogen form on N2O Evolution by Denitrification

Nitrous oxide evolution from the soils treated with nitrogen fertilizer such as ammonium sulfate or sodium nitrate under different environmental conditions was measured by the combined method of ga...

Improved method for easy and rapid determination of root length of vegetables

Abstract We developed an improved method for the determination of the root length of crisphead lettuce (Lactuca sativa L.) and Chinese cabbage (Brassica pekinensis Rupr.). Boiling of soil containing roots and stirring to collect the roots in water reduced the contamination with debris. The time required for removing the debris was shortened by 30% as compared to washing of roots with water. Boiling had no effect on the nitrogen concentration, but resulted in changes of the phosphate, potassium and calcium concentrations of roots. Use of a crosscounter plate shortened by 30% the time required for the line intersect method. The total time required for root length determination from a 1 kg soil sample was only 15.9 min.

Significance of litter layer in enhancing mesofaunal abundance and microbial biomass nitrogen in sweet corn-white clover living mulch systems

Living mulch is a type of sustainable farming system that consists of cover crops planted either before or with a main crop; a living mulch is maintained as a living ground cover throughout the growing season of the main crop. Microbial biomass and abundance of mesofauna (microarthropods and enchytraeids) are important soil biological parameters in relation to soil function, plant productivity, and nutrient cycling; however, the effects of living mulch on these parameters are not fully understood. In this study we examined the effects of living mulch treatment with nitrogen fertilizer (0, 40, 160, or 200 kg ha−1) on the abundance of soil microarthropods (Oribatida, Mesostigmata, Prostigmata, and Collembola) and the effects of living mulch treatment on the dynamics of the soil biota (mesofauna, microarthropods, enchytraeids, and microbial biomass nitrogen) from spring to autumn. Our results showed that living mulch treatment significantly (p < 0.05) increased the grain weight of the main crop in both experiments. Generally, living mulch treatment had a positive effect on the abundance of mesofauna and microbial biomass nitrogen, despite pesticide usage. Nitrogen levels did not affect the number of microarthropods. The litter layer in living mulch significantly (p < 0.05) enhanced microbial biomass nitrogen and the abundance of Oribatida, Prostigmata, and Collembola. We conclude that living mulch enhances mesofaunal abundance and microbial biomass nitrogen and that the production of a litter layer by living mulch is one of the major mechanisms for this enhancement.

Multicolor staining of root systems in pot culture

Abstract We have developed a method for staining the root systems of neighboring plants distinguishably in pot culture to facilitate studies of the interactions between plants. Pot soil was desiccated until the plant wilted, and then the shoot was cut and a dye solution (Fantasy) was pressure-injected into the roots at 0.05 MPa (gauge). All the roots, including fine roots of double-planted tomato (Lycopersicon esculentum var. Momotaro), in a 10-cm-diameter pot were well stained, but the root hairs were not. The volume of dye and the time required for staining were 6.4 mL and 5 h, respectively (root length 179 m plant−1; root fresh weight 2.62 g plant−1 on average). The root distribution of double-planted tomato in a 40 L container was well determined. The volume of dye and the time required for staining were 100 mL and 40 h, respectively (root length 1,514 m plant−1; root dry weight 4.93 g plant−1 on average). Each plants roots accounted for 37–52% of the total root weight at an intermediate position between the two plants, whereas at the other positions, the roots of either plant were dominant (82–99% of total root weight). In principle, the proposed method is applicable to whole plant species with vascular systems.

Improvement of root staining method for field applications

The root interaction between neighboring plants is neither obvious nor well studied because there are no easy and convenient methods to distinguish the root system among individual plants. Previously, we developed a method of pressure–injection of dye into the roots of pot-grown plants in dry soil condition. Here, we modified the method for high-pressure injection in wet soil or outdoor fields to counter root pressure. In our preliminary pot experiment, the roots of tomato plants (Lycopersicon esculentum “Momotaro”) were stained well in wet soil by dye injection at 0.5 MPa. In the field test, tomato plants were grown in a 2 m × 2 m concrete frame field. Four successive plant shoots were cut 159 and 170 days after sowing, and dye solutions (Fantasy) of different colors were pressure-injected into the roots from the stumps from 0.05 to 0.5 MPa. The volume of the dye and the time required for staining were respectively in the ranges of 120 to 150 mL and 9 to 96 h. Soil blocks or cores were sampled and the roots were collected by hand picking and the water floating method, and distinguished by color. The recognition and collection of roots were easy because most of them were stained dark. In the 0–15 cm soil layer, most of the roots in the four blocks surrounding the hills came from the hills. In blocks found at the intermediate position between two adjacent plants, the roots of both plants were distributed. In the 15–30 cm soil layer, most of the roots in the four blocks surrounding the hills came from the hills, although roots of other plants also existed. The roots of each plant extended to adjacent plants, even reaching distant plants. The roots of a plant did not grow toward another plant in the opposite row. Findings of this study are useful in relation to effective fertilizer application. The proposed injection method is expected to facilitate the study of the interactions between root systems in the field.

Root distribution of field-grown crisphead lettuce (Lactuca sativa L.) under different fertilizer and mulch treatment

Abstract We determined the seasonal changes in the root system of field-grown crisphead lettuce under different fertilizer treatment (stripe, broadcast, and no-nitrogen (absence of nitrogen)) and polyethylene film mulch treatment. Soil blocks less than 1 L volume were sampled from 1 quarter of a plants rooting volume and roots were separated from the soil blocks by boiling. The root length was determined by the modified line intersect method. Root development in the broadcast plots was better in the 0–30 cm layer but worse below this depth compared to the no-nitrogen plot. In the stripe plots, the rooting pattern was similar to that in the broadcast plots in the 0–30 cm layer and similar to the no-nitrogen plot below that depth. Roots in the stripe plots showed characteristics of both broadcast and no-nitrogen application. With the mulch, the root length density was the highest in the 0–10 cm layer, while without mulch it was highest in the 10–20 cm layer. The root / shoot ratio for nitrogen absorption was ca. 10%. The 0–30 cm layer accounted for more than 80% of the total root length due to the abrupt increase in soil hardness below this depth. Total root length ranged from 1,021 to 1,931 m plant−1 at harvest (50 cm deep). The fine root length / weight ratio was 363 m g−1 dry root and the fine root diameter averaged 207 μm. Constraints on methodologies such as sampling depth, removal of debris, saving of labor, and core sampling were outlined.

Root length and distribution of field-grown buckwheat (Fagopyrum esculentum moench)

Abstract We determined the seasonal changes in the root system of field-grown buckwheat (Fagopyrum esculentum Moench). Rooting soil volume was collected in 1 L soil blocks to a 40 cm depth, and roots were separated from soil by boiling. The root length was determined by the modified line intersect method. Root length increased constantly until peak flowering, then did not increase, reaching a value of 18.9 km m−2 at harvest, corresponding to a surface area of 4.1 m−2 m−2 and an average length density of 4.7 cm cm−3. The fine root diameter decreased from 83 to 66 μm with the growth stage and the length/ dry weight ratio increased from 849 to 1,199 m g−1. Root length density was highest in the 0–10 cm and /or 10–20 cm soil layers and decreased below this depth. Nutrient uptake per unit root length was highest at the early growth stage, 0.51 mg m−1 for N and highest at the flower budding to peak flowering stages, 0.12 mg m−1 for P Constraints on methodologies such as debris removal and labor reduction were outlined. A field containing few debris must be selected for root studies because the removal of a large amount of debris is laborious.

A New Method for the Simultaneous Determination of the Amount of N2O Evolved from Soil and its N-15 Abundance

A new method for the simultaneous determination of the amount of N2O evolved from soil and its N-15 abundance was developed. Gases evolved from soil were collected in a 1-liter Tedlar® bag using a special gas collecting device. Nitrous oxide (N2O) in the collected sample gases was concentrated in the glass tube trap with liquid nitrogen. The collected N2O was released and measured by thermal conductivity detector gas chromatography. By this system, a quantity of 0.1 μg N/liter sample could be determined for N2O. The N2O separated by gas chromatography was introduced into a discharge tube and subjected to the N-15 analysis by emission spectrometry. By this system 15N atom % of 0.3 μg N2O-N/1 liter sample could be measured.

Growth survey of crisphead lettuce (Lactuca sativa L.) in fertilizer trial by low-altitude small-balloon sensing

Abstract Both efficiency and precision of field-grown plant biomass survey are expected to be improved when aerial images of whole fields are acquired. Many such studies have been conducted in paddy rice (Oryza sativa L.), wheat (Triticum aestivum), and beans (Glycine max (L.) Merr. and Phasaeolus vulgaris), but few in vegetables. In this study, we examined whether or not aerial image analysis is useful for the biomass survey of vegetables. Aerial images of field-grown crisphead lettuce (Lactuca sativa L.) in a three-year fertilizer trial were acquired at head formation and harvesting stages in summer and autumn cropping with a compact digital camera hung under a tethered small balloon (2.2 m in length, 0.56 m3 in volume). The camera height ranged from 36 to 65 m, and the ground resolution ranged from 1.3 to 2.2 cm pixel −1. The horizontally projected area of the plant was measured as follows: Aerial images of the field were topographically corrected, the lettuce part was extracted based on the difference in color, the images were binarized, and the projected area was determined by image processing software. The estimation of fresh weight of one plant from the projected area was difficult because of the large data dispersion. When the averaged projected area in each plot was used, estimation was improved in some cases. Estimation of fresh weight at the harvesting stage by using the projected area at the head formation stage was difficult due to the low correlation coefficient. The results of factor analysis of fertilizer treatments by using projected area agreed well with those done using fresh weight when the correlation coefficient between the projected area and the fresh weight was high. It was concluded that the estimation of absolute lettuce fresh weight was difficult, but relative comparisons among treatments were possible until the head formation stage, using aerial images acquired by low-altitude small-balloon sensing.

Root distribution of field-grown Chinese cabbage (Brassica campestris L.) under different fertilizer treatment

Abstract We determined the seasonal changes in the root system of field-grown Chinese cabbage under different fertilizer treatment (stripe, broadcast, and no-nitrogen application (absence of nitrogen)). Soil blocks less than 1 L volume were sampled from 1 quarter of a plants rooting volume and roots were separated from the soil blocks by boiling. The root length was determined by the modified line intersect method. The fertilizer treatment did not affect substantially the root development. In deep soil layers, roots developed better in the broadcast plots than in the stripe plots in 1995, but the trend was not clear in 1996. With polyethylene mulch, the root length density of Chinese cabbage was the highest in the 0–10 cm soil layer and it decreased drastically below a 30 cm depth, due to the abrupt increase in soil hardness below this depth. The 0–30 cm layer accounted for more than 70% of the total root length. The root/shoot ratio for the nitrogen content was ca. 1.7%. Total root length ranged from 4,842 to 5,579 m plant−1 at harvest (70 or 80 cm deep). The fine root length / weight ratio was 939 m g−1 dry root and the fine root diameter averaged 92 μm. The differences in the strategy of root development in Chinese cabbage and crisphead lettuce were discussed. Constraints on methodologies such as sampling depth, removal of debris, and saving of labor were discussed.