Search

Intensive vegetable production systems throughout South East Asia are characterised by large nutrient inputs and low nitrogen (N) use efficiencies. In Indonesia, intensive vegetable production is concentrated on volcanic highland soils starting from an altitude of around 700 m above sea level. We measured potential N mineralisation from soil organic matter and from several representative organic materials in Andisols and Inceptisols with andic properties from Central Java, Indonesia. Unamended soils and soils amended with crop residues, animal manures, and compost were incubated during 3–4 months at 25°C in the laboratory, then we monitored N mineralisation. Relative N mineralisation was significantly smaller in the Andisols (average 3.6 ± 1.0%) than the Inceptisols (7.4 ± 2.9%), and was negatively related to oxalate-extractable aluminium (Alox) (r = –0.749) and soil organic carbon (r = –0.705). This is probably due to the strong protection of organic matter (and organic N) by binding to active Al compounds. Net N mineralisation from the added organic materials was highly variable (ranging from 68.1% for the broccoli residues to 2.6% for tithonia compost), and was best related to the organic N content (r = 0.476). There were no significant correlations between net N mineralisation and biochemical fractions, which we attribute to the large variety of materials used in this study compared with previous studies. The data generated here on N mineralisation potential from soil organic matter, and from a variety of plant materials and animal manures that are commonly used in these intensive vegetable rotations, will allow for the rapid and efficient introduction of N fertiliser advice systems based on balance sheets.

Reduced tillage (RT) management may increase surface soil organic carbon (SOC) and nitrogen (N), particularly due to accumulation of labile organic matter (OM). We investigated the effect of RT compared with conventional tillage (CT) on the distribution of SOC and N over different soil fractions from 7 pairs of fields with cereal–root crop rotations, in the Belgian loess belt. Surface soil samples (0–100 mm) were physically fractionated according to a sequential sieving and density separation method into stable microaggregates, silt and clay, and free and occluded particulate OM fractions. RT management was previously found effective in increasing the organic C and organic N content of the surface soil (0–100 mm) at these 7 sites. Here, physical fractionation showed that the difference in amount of organic C and N in free particulate OM (fPOM), intra-microaggregate particulate OM (iPOM), and silt and clay associated OM between the RT and CT soils contributed 34, 29, and 37% of the increase in SOC and 35, 32, and 33% of the increase in N. The contribution of OC and N in iPOM and fPOM increased significantly on a relative basis under RT management. Only a modest increase in iPOM and slight enhancement of microaggregation was observed in RT compared with CT soils. We suggest that the repeated disturbance of soil by harvest of root crops and repeated use of cultivators and harrows may limit the accumulation of physically protected POM under RT management of these Western European cereal–root crop rotations. Instead, most of the accumulated OC and N in the surface horizons under RT management is present as free unprotected POM, which could be prone to rapid loss after (temporary) abandonment of RT management.

One of the most important problems in the Loess Plateau of China affecting sustainable agriculture is inefficient nutrient use. Field experiments were conducted to study the effects of different soil management practices on the nitrogen (N) dynamics and winter wheat yield on a loess soil in Luoyang, Henan province, China. The results showed that subsoiling with mulch (SS) consistently increased the yield of winter wheat primarily by better water harvest compared with conventional tillage (CT). The influence on yield of no till with mulch (NT) depended on the amount of precipitation. TC (2 crops per year) lowered the winter wheat yield mainly due to the unfavourable soil moisture conditions after growing peanut in summer; however, the harvested peanut gained an extra profit for the local farmer. N uptake by grain and straw and N export was highest for SS. Changes in frequency and intensity of tillage practice altered soil total N content and its distribution along the slope. SS and NT increased the N content of the surface layer (0–0.20 m) compared with CT, but there was no significant effect in deeper soil layers. Considerable amounts of nitrate-N were left in the profile 0–1.60 cm just after harvest under all treatments. The cumulative nitrate-N content to a depth of 1.60 m on average was 282 kg/ha, of which 56 kg/ha was in the layer 1.20–1.60 m, which is an indication of considerable nitrate leaching. From data of 7 consecutive years between 1999 and 2006, it could be concluded that SS resulted in the highest yield and total N content in the surface layer, and is the most sustainable tillage option for the circumstances of the study area.