粒径膜厚与控释肥料的氮素养分释放特性

Effect of granule size and coating thickness on nitrogen release characteristics of controlled release fertilizers (CRFs)

利用专利技术,以芬兰长之道Uki厂生产的粒径分别为2 5～3 0、3 0～4 0、4 0～5 0mm的氮磷钾复合肥制造控释肥料。在25℃和40℃恒温条件下培养0、1、2、3、4、5、6、7、14、21、28、35、42d后测定氮素释放率,以探讨粒径、包膜厚度(膜材用量)、交联剂等对氮素释放率的影响。结果表明,常温和高温下,包膜厚度相同时,氮素释放率随着肥料粒径的增加而明显增加;但氮素释放率随粒径增长的幅度在膜材用量增大的情况下减小。无论是小粒还是大粒控释肥料,其氮素释放的速率随膜材用量的增多而减小。包膜材料添加交联剂可以明显增加氮素释放率,交联剂S的用量对氮素释放率的影响小于交联剂P。同一包膜厚度和单位质量下,用大粒径核心肥料制造的控释肥料可明显减少包膜材料的用量;但要改进大粒径控释肥料的氮素释放率,应利用表面平滑的核心肥料制造包膜控释肥料。

Research of controlled release fertilizers (CRFs) has been paid great attention in China recently because of their advantages of high nutrient use efficiency, less burning damage to plants and easier to handle. However, the application of CRFs to arable crops has been restricted by high cost of the products. How to reduce the cost of CRFs becomes a crucial factor to promote CRFs in farming practice. The high cost of the CRFs is due to high value of coating material and energy consumption. A lot of researchers have paid great attention to study on manufacture CRFs by cheaper coating materials such as FMP and clay mineral, being producing slow release fertilizer. Nevertheless, longevity of such CRFs is shorter than that of the ones coated by resin or polymer. In other word, CRFs were manufactured by use of FMP and clay as coating material can not control nutrients release properly. So far, no research concerns decreasing cost of coated CRFs by reducing total surface area of a unit weight of kernel fertilizer granule in literature. In order to realize target to decrease manufacture cost by declining surface area of a unit weight of kernel fertilizer, the present study tested nutrients release characteristics of a serials CRFs with different granule diameter under several coating thickness. The CRFs in study were manufactured by coating Kemira Grow-How NPK (15-15-15) granule as kernel compound. The kernel granules divided into three groups of 2.5 to 3.0 mm, 3.0 to 4.0 mm and 4.0 to 5.0 mm in diameter. Each group granule coated by 51 g, 61 g and 71 g resin per square meter surface of the kernel granule according to a patent technique of South China Agricultural University to produce CRFs with three thickness of coating. The coating (materials) treated with adding starch and PVA or without them as additives respectively. The CRFs were incubated in distilled water with a ratio of fertilizer to water at 1∶20 for 0,1,2,3,4,5,6,7,14,21,28,35,42 days under constant temperature at 25℃±1℃ and 40℃±1℃ respectively. The ammonium and nitrate were determined at the given time to (evaluate) the effect of granule size, thickness of coating and additive materials on the nitrogen release rate (NRR). Results showed that NRR increased with granule size in treatment of CRFs having the same coating thickness under both normal and higher temperature. However, the effect of granule size on NRR decreased with increasing coating thickness. Surface structure of the kernel granule affecting NRR of the CRFs. Increase of coating thickness could decrease NRR. No matter what size of the CRFs, the nitrogen release rate decreased significantly with increase of coating thickness. Additives of both starch and PVA could enhance the NRR. The application amount of PVA had remarkable influence on the NRR compared to starch. To reduce amount of coating material by use of bigger granule could rely on the use of smooth surface kernel granule. Therefore, reducing cost of CRFs could be achieved by manufacturing CRFs through coating smooth surfaced big granule NPK compound.