No abstract

Nitrogen fertilizer application rates in intensive vegetable production in (South) East Asia have increased exponentially over the past decades, including in the low income countries. While there have been reports of excessive N inputs from e. g. Vietnam, Thailand and Indonesia, very little quantitative knowledge exists on the real extent of the problem. We calculated N balances and agronomic N use efficiencies (ANUE) for a number of typical intensive vegetable rotations in the highlands of Central Java, Indonesia, on fertile Andisols, both for individual cropping cycles (short term) as for 6 consecutive cropping cycles (long term). This was done for farmers practice (FP) treatments, and improved practice (IP) treatments, where N fertilization was significantly reduced. Yields were in general similar in FP and IP, but tended to be slightly higher in IP, with some significant differences. Both the short and long term N balances were always positive and usually very high. Short term N balances ranged from 9 to 559 kg N ha(-1) and 219 to 885 kg N ha(-1) in IP and FP, respectively, while short term ANUE ranged from 8 to 67 and 4 to 39% in IP and FP, respectively. Long term N balances ranged from 627 to 1,885 kg N ha(-1) and 962 to 3,808 kg N ha(-1) in IP and FP, respectively, indicating a massive excess of N supply especially in FP. N balances can thus be drastically reduced with no negative impacts on yield, on the contrary. Soil mineral N in the 0-25 cm layer was in general not very high (6.5-38.8 mg N kg(-1) soil) and not systematically different between IP and FP, probably as a result of excessive NO(3)(-) leaching. Therefore, topsoil mineral N seems to have only limited indicator value under these conditions. Because denitrification losses in these soils are not very high, most N in excess of the crop requirements will be lost by leaching. Quantitative data on N balances as obtained here may be used to sensitize policy makers and farmers about the threat of current farming practices to the environment, and to improve economic performance

<p>Rate of NPK fertilization on rice using NPK compound fertilizer needs to consider soil nutrient status and plant nutrient requirement. The research was aimed to determine the optimum rate of compound fertilizer and the effect of enriched S nutrient of NPKS compound (15-15-15-5S) and NPK compound fertilizer (15-15-15) on the growth and yield of rice. The experiments were conducted at two sites in Galuga, Ciampea Bogor, West Java from April to September 2013, using randomised complete block design with 3 replications. Experiment at site I consisted of 9 treatments: six levels of fertilizers NPKS i.e. 0; 150; 300; 450; 600; and 750 kg/ha, standard fertilizer, NPK compound fertilizer equivalent to standard, and standard fertilizer plus S. Rate of urea, SP-36, and KCl for standard fertilizer treatment was respectively 250, 75, and 50 kg/ha. At site II the treatments consisted of 6 levels of NPK compound fertilizer i.e. 0; 150; 300; 450; 600; and 750 kg/ha and the standard fertilizer with rate of 250 kg/ha of urea, 50 kg/ha SP-36, and 75 kg/ha KCl. Plot size was 4 m x 5 m planted with Ciherang variety. Data collection included chemical properties of soil before and after the experiment, plant height, number of tillers, straw weight, and dry grain weight and the nutrient uptake. The effectiveness of fertilizer was calculated by RAE (Relative Agronomic Effectiveness). Results showed that fertilizer NPKS (15-15-15-5S) at 600 kg/ha effectively increased dry grain weight from 3.63 t/ha to 4.67 t/ha, but was not significantly different from a standard fertilizer treatment. It increased dry grain weight by 29% compared to control. NPK fertilizer (15-15-15) effectively promoted growth and dry grain weight equivalent to standard fertilizer at rate of 300-750 kgha. The optimum rate of NPK compound fertilizer (15-15-15) was 440 kg/ha as was shown with the production performance of 4.12 t/ha with RAE by 58%. NPKS compound fertilizer with rate of 750 kg/ha showed the highest uptake of N, P, and K nutrients and significantly increased the available P in the soil. Whereas NPK compound fertilizer with a rate of 600 kg/ha indicated the highest P nutrient uptake. Fertilizer enrichment with sulfur on NPKS fertilizer (15-15-15-5S) did not significant affect on grain dry weight.</p>

A number of recent studies suggest that soil aggregation may affect short-and long-term phosphorus (P) availability in highly weathered soils. We investigated the effect of natural soil aggregate sizes (from < 0.212 to 4-5.6 mm) on P extractability and plant P availability in low-P and high-P Siniloan soils (Typic Palehumults) from Laguna, Philippines. Mehlich-1 extractable P was always greatest in the smallest aggregates, regardless of whether or not it was extracted without P addition or extracted after 15 days incubation with newly applied P in both intact and ground aggregates. Grinding significantly increased the initial extracted P only in high-P soil. Soil aggregate size had little effect on the extractability of newly added P because the short-term Mehlich-1 P buffering coefficient (PBC), a change in Mehlich-1 extracted P (mg kg -1 soil) per unit of added fertilizer P (mg kg -1 soil), was not significantly correlated with aggregate size. In the greenhouse experiment, plant growth (shoot dry weight, root length and dry weight) and total P in the shoots of both corn (Zea mays L.) and rice (Oryza sativa L.) were markedly increased with decreasing aggregate diameters from 4-5.6 mm to < 0.212 mm, even when the plant had adequate P in the rice experiment in the high-P soil. There was no interaction between P supply and aggregate size on the plant growth response and P uptake in both rice and corn grown in the two soils, suggesting that the effect of soil aggregation on plant P availability of newly added P was small. Although, the smaller aggregates themselves also contained higher total P, finer and longer root growth in these aggregates as a direct effect of aggregate size on root growth mainly contributed to better plant growth and P uptake in these aggregates. The findings of this study suggest that in Siniloan soil, soil aggregation had little effect on short-term PBC and plant P availability of the P newly added to soil over 5 weeks. However, in high-P soil, the current soil test procedures, which require grinding and shaking of soil sample, might overestimate the available P status of the soil.Effect of soil aggregate size on P availability 149

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 degrees 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 (Al-ox) (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