4 Crop management
Agronomic trials in Aceh after the tsunami found a range of nutritional disorders, particularly lack of grain filling in rice and peanuts. Possible reasons for the nutrient problems included loss of organic matter and trace elements, high inputs of urea in relation to potassium, and lack of phosphorus and calcium in salinity-affected sandy soils.
Two years after the tsunami, most soil fertility problems in tsunami-affected areas were due to nutrient deficiencies and imbalances related to the loss of organic matter, and the effects of salts and sediments. Observations of the variation in crop performance highlighted the importance of monitoring growth, yields and nutrient levels to identify trends and develop site histories. Where there was potential to establish new production systems, such as different crops or rotations, trials were developed to demonstrate these new systems. For instance, the different soil treatments required for rice (compaction) and palawija (non-rice) crops (loose soil) led to trials using permanent beds for palawija crops, rather than alternate puddling and cultivation of one site to the detriment of soil health.
Pre-tsunami fertiliser recommendations were often found to be irrelevant or wrong after the tsunami because of the soil changes. It was therefore important to test tsunami-affected soils for at least the major nutrients before preparing the soil, fertilising or planting (Figure 11). Testing the soil ensured that the correct amount of fertiliser was applied; farmers learned that overfertilising is a waste of money because nutrients not used by the plants leach out of the crop root zone.
Crops initially grew well in peaty sediments as a result of the high nutrient levels of the sediment. Some coastal rice crops yielded very well within 12 months of the tsunami (Bradbury et al. 2005), probably as a result of a beneficial effect from tsunami-deposited peat sediments. The effects from these sediments were short lived—subsequent crops did not yield as highly without the addition of fertiliser. Inland peat soils offered cropping opportunities for farmers who lost land in the tsunami, but only if they were managed carefully to ameliorate the inherent high acidity. Phosphorus, trace elements and organic matter may be needed on salinity-affected sandy soils to help crops fill.
Case study: Empty peanut pods
At Bireuen in Aceh, many peanut plants had empty pods in a crop harvested in February 2006. Farmers in the area reported that this was the first time these problems had been encountered. The peanuts were normally grown in deep, sandy soil (sand dunes) without fertilisers, and cropped twice per year, with weed fallows between crops. The plants had good vegetative growth and appeared to have enough nodules, but the root systems were very shallow. Weeds were well established in the crop and in bare areas. Measurements of soil salinity using an EM38 instrument showed low salinity. A possible cause of the empty pods was lack of calcium, which is essential for kernel development; calcium is absorbed directly from the soil through the pod wall. High soil magnesium can also reduce kernel quality and lead to empty pods.
A trial investigating the effects of fertiliser, gypsum, and chicken and cow manures found that the best pod development was obtained by a soil treatment with combined chicken and cow manures, indicating a need for organic matter in the soil. Organic matter helps conserve soil moisture and improves the ability of peanut plants to absorb nutrients.
Lack of organic matter in soils was identified as an important constraint to production in the tsunami-affected soils in Aceh. The tsunami’s scouring action removed organic matter, leading to a drop in soil fertility. Organic amendments can substitute 25–100% of the nutrients of chemical fertilisers, depending on the kind, amount and content of the material. In Aceh, manure, composts, crop residues and mulches increased soil nutrient levels and generally improved soil health and long-term soil fertility. As well, they encouraged biological life, and improved soil structure and soil moisture-holding capacity. Farming systems that incorporated crop rotations and stubble management also increased soil organic matter.
A corn trial at the Assessment Institute for Agricultural Technology (BPTP) Banda Aceh grounds found that near-surface salinity was significantly lower when manure was incorporated beneath the corn row. Where organic matter was in limited supply, farmers incorporated compost or rotted manure in the planting row to provide nutrients close to the young plants, and encourage leaching of any salt in the soil.
Demonstration trials were useful for comparing crop production using fermented fertilisers, chemical fertilisers, no fertilisers, and a 50:50 mix of chemical and fermented products. It was important to keep records of fertilisers used and the fertiliser recommendations provided to farmers so that advisers and farmers could link fertiliser applications with crop production.
Making compost after the tsunami provided a source of organic matter for soil, created a useful product from organic debris and offered productive activity for farmers. Aceh farmer groups made a range of composted fertilisers. One group used rice husks, peanut pods, and cow or chicken manure; another made bokashi fertiliser from cow manure, rice ash, wood ash, rice stubble and micro-organisms; another group made liquid fertiliser from buffalo manure, lime and home-made fish emulsion.
Other soil amendments
Rice husk char (2 t/ha) and gypsum (1.5 t/ha) increased grain yields of rice grown on tsunami-affected soils in Sri Lanka (Reichenauer et al. 2009). Gypsum will ameliorate saline soils with a pH greater than 8.5 and exchangeable sodium percentage greater than 15. The soil pH is likely to increase during the leaching process (Chaudhary et al. 2006).
Rice husk char has shown potential as a soil amendment for wetland rice in Aceh, and for peanut and tree crops on sandy soils in dryland areas of Vietnam (Keen et al. 2013). Char derived from other waste organic materials may also be beneficial to the establishment of crops in tsunami-affected saline soils.
Approximately 2 million livestock animals (buffalo, cattle and goats) were lost in Aceh as a result of the tsunami. Smaller numbers of large livestock (beef and dairy cattle) were lost in the 2011 Japan tsunami, along with nearly 5 million poultry (Danone 2011). The loss of livestock in Aceh led to a shortage of manure, an important agricultural input in the sandy coastal soils. It is important to reintroduce poultry, goats and cattle as quickly as possible after a tsunami because their manure adds nutrients to the soil, builds organic matter levels and contributes to compost making. One water buffalo can produce about 2 t of manure per year.
The Aceh experience was that farmers would incorporate manures only if they could see a result and only for high-value cash crops, because of the cost of collection and transport of manure. Since it is financially difficult for many farmers to acquire livestock, a useful post-tsunami aid project could be replacing lost livestock, once there is sufficient food available for animals. Reintroduction of poultry where all birds have been killed is particularly useful; the birds’ manure is an important nutrient source and organic soil amendment, and the birds also provide eggs and meat.
Grazing is a good use of land that is too waterlogged for cropping or does not have a reliable irrigation source. However, it was not an option for many Aceh farmers because the area of farming blocks is 1 ha or less, and this land is used to grow rice for food and income. A salt-tolerant grass (Diplachne fusca) became more prevalent after the tsunami. Although the mature grass is not palatable to cattle, the grass is grown widely in Pakistan as a forage crop that is eaten when young. Aceh farmers confirmed that cattle will eat the young shoots.
A mulch of dried organic matter such as coconut leaves will lower the soil temperature and hold moisture in the soil, both of which will make the soil more livable for soil organisms. Mulch also protects the soil from drying out and hardening—this is particularly useful for compacted rice paddy soils that are used to grow palawija crops during dry seasons.
The difficulty in Aceh was finding enough suitable organic material to use for mulch, because the local custom is to burn dead leaves to provide ash for use as fertiliser during planting. One option is to grow a green manure crop to act as mulch between crops, but for many farmers this will tie up productive land for too long. Another option is to grow stockfeed or a cash crop that can double as a green manure crop. However, caution needs to be used in growing green manure or stockfeed crops that could become weed pests.
It is important not to use peanut crop residues on soil to be used for peanuts, because of the risk of infecting the new crop with leaf pathogens. Peanut residues are better collected and composted before use.