Vinyl-film mulch: a practice for sweet potato (Ipomoea Batatas Lam. var. Edulis Makino) cultivation to reduce nitrate leaching
Abstract Under conventional cultivation practices in Southern Kyushu, Japan, a considerable amount of nitrate-N is leached from agricultural fields into ground water. The leaching processes are accelerated by high permeability of the volcanic ash soil, high rainfall and high summer temperatures. The present work was instigated to study the possibilities of controlling nitrate-N leaching by regulating the infiltration of rain water in the soil, the source of percolation below the root zone. Nitrate-N leaching from the root zone of sweet potatoes to deeper soil layers was compared in three treatments: maximum soil surface mulching with 0.03 mm vinyl-film with holes at ridge tops to supply plants with enough soil moisture to meet the crop water requirement (maximum vinly-film mulch, MVM); applications of fertilizer containing a nitrification inhibitor dicyaniamide (DCD); and conventional cultivation practices. NPK compound fertilizer (N 8 P 5.2 K 16.6 ) containing the ammonium form of nitrogen 900 kg·ha −1 and PK compound fertilizer P 8.7 K 16.6 600 kg·ha −1 were applied in the MVM and conventional plots. DCD-fertilizer (N 15 P 6.5 K 12.5 ), maintaining the same rate of absolute N with adjustment of P and K using fused magnesium phosphate (P 8.6 ) and potassium chloride (K 41.5 ), were applied to the DCD plots. MVM increased surface run-off, resulting in least percolation among the treatments. The highest nitrate-N concentration, taken as an average for 2 years, in soil-water periodically sampled throughout the growing period at 210 cm depth below surface, was found 1.8 ppm in MVM, whereas in DCD and in conventional treatments the same was measured as 8.7 and 5.2 ppm, respectively, indicating the lowest level of nitrate leaching to be in the MVM treatment. The highest availability of mineral nitrogen in the root zone of the MVM treatment was confirmed by the highest plant-top-uptake of nitrogen, Leaf Area Index and vine growth. DCD fertilizer did not contribute to the control nitrate-N leaching. There was no significant difference in root yields among the three treatments.
NITROGEN AND CHLORIDE DISTRIBUTION AND BALANCE IN A CLAY LOAM SOIL
In field experiments conducted on a poorly drained clay loam soil from 1974 to 1976, inclusive, 21–44% of added chloride was lost from the 0- to 75-cm layer by the end of September, whereas NO3−-N increased in this layer in both the control and fertilized plots. Mineralization during the summer masked any N losses by leaching or denitrification. N losses were highest between late fall and early spring. NO3−-N and chloride tended to show similar distribution patterns in the profile but not necessarily similar leaching losses, since simultaneous denitrification occurred in an adjacent experimental site. Chloride distribution in the profile and leaching losses did not appear to coincide with expectations of typical transport theory, since losses were associated with diffuse bulges near the surface instead of distinct peaks or slugs of chloride moving steadily downward.
Zur nitrifikationshemmenden Wirkung von Dicyandiamid zu Gülle in der Zeit zwischen Spätherbst und Frühjahr
In Modellversuchen wurde der Einflus verschiedener Bodentemperaturen auf die Nitrifikation von Gulle ohne und mit Zusatz des Nitrifikationshemmstoffes Dicyandiamid sowie der Abbau von Dicyandiamid untersucht. 
 
 
 
1. Der NH4-N der Rindergulle wurde bei 4°C bzw. 0°C in der Klimakammer innerhalb von 10 bzw. 30 Wochen vollig nitrifiziert. Dicyandiamid verzogerte die NO3-Bildung im ersten Fall um ca. 15 Wochen (Dicyandiamid war nach 25 Wochen vollstandig abgebaut), im letzteren Fall uber 30 Wochen hinweg. 
 
 
 
2. Wurde in der Klimakammer der Gang der Bodentemperatur von Oktober bis April simuliert, erfolgte bereits innerhalb der ersten vier Wochen eine vollstandige Nitrifikation des Ammonium, mit Dicyandiamid hingegen erst nach 30 Wochen. 
 
 
 
3. Gulle mit Boden gemischt und in Polyathylenflaschen in die Ackerkrume eingegraben wurde, wenn Anfang November ausgebracht, bis Februar, wenn Anfang Marz ausgebracht, bis April nitrifiziert. Mit DCD-Zusatz war jedoch Mitte Mai erst 1/4 der Marz-Gulle bzw. kaum die Halfte der November-Gulle umgesetzt. Zum gleichen Zeitpunkt waren noch jeweils ca. 30% der vorgelegten Dicyandiamid-Menge nachweisbar. 
 
 
 
Effect of dicyandiamide on the nitrification of liquid manure between late autumn and spring 
 
 
 
The influence of soil temperature on the nitrification of slurry manure with and without addition of the nitrification inhibitor dicyandiamide and the decomposition of dicyandiamide was tested in model experiments. 
 
 
 
1. NH4-N of cattle slurry was completely nitrified within 10 or 30 weeks at 4°C or 0°C respectively in a growth chamber. The addition of dicyandiamide retarded the formation of NO3 in the first case for about 15 weeks (dicyandiamide was completely decomposed after 25 weeks), in the latter case for more than 30 weeks. 
 
 
 
2. A simulation of field soil temperatures from October till May in an incubation trial resulted in full nitrification within four weeks, with dicyandiamide within 30 weeks. 
 
 
 
3. Slurry mixed with soil, burried in polyethylene-bottles into the top soil of the open field, was nitrified until February when applied at the beginning of November, or until April when applied at the beginning of March. With DCD-addition, however, only one fourth of March-Slurry or hardly half of November-Slurry was nitrified. At the same time, in each case about 30% of the applied amount of DCD was still detectable.