Three years field experiments were conducted to study the effect of chemical and mechanical weed control on soil quality and erosion under cassava cropping system. The experiment were conducted at the University of Brawijaya field experimental station, Jatikerto Village of Malang Regency, Indonesia. The experiments were carried out from 2011-2014. The treatments consist of two cropping system (cassava mono culture and cassava + maize intercropping), and two weed control method (chemical and mechanical methods). The experimental result showed that the yield of cassava first year and second year did not influenced by weed control method and cropping system. However, the third year yield of cassava was influence by weed control method and cropping system. The cassava yield planted in cassava + maize intercropping system with chemical weed control methods was only 24.25 t.ha-1 , which lower compared to other treatments, even with that of the same cropping system used mechanical weed control. The highest cassava yield in third year was obtained by cassava + peanuts cropping system with mechanical weed control method. After three years experiment, the soil of cassava monoculture system with chemical weed control method possessed the lowest soil organic matter, and soil aggregate stability. During three years of cropping soil erosion in chemical weed control method, especially on cassava monoculture, was higher compared to mechanical weed control method. The soil loss from chemical control method for the third year was 54.20 t.ha-1 , whereas from the mechanical weed control was only 38.40 t.ha-1 .

A field experiment was done to study the residual effect of biochar application on the growth and yield of red chili (Capsicum annum L.). The experiment was done at Wringinrejo Village, Blitar Regency of Indonesia. The biochar treatment was applied to cassava crops from 2009 until 2013. The subsequent soil then was used for chili planting in 2013 with the treatment of: (i) Biochar residue (with and without biochar), and (ii) fertilizer application (No fertilizer, Nitrogen, Farm Yard Manure (FYM), and combination of N+FYM). These treatments were arranged in a split plot design with biochar residue as the main factor, and fertilizer application as the sub factor; with 4 replications. The collected data were: (i) the growth and yield of chili, (ii) yield component, and (iii) soil quality. The results show that after4 year of application, biochar still had a significant effect on the growth and yield of red chili. In general, chili planted on plot that given biochar before, tend to be higher with more branches compared to the chili planted on non-biochar applied plot. Thus it can be concluded residual effect of biochar significantly influenced the growth and yield of red chili. Application of nitrogen fertilizer and farm yard manure increase the chili yield, both on non-biochar, and applied biochar plot. The highest fruit yield (14.6 t.ha-1) was obtained by chili planted on biochar-treated plot applied with nitrogen and Farm yard manure.

Risk and uncertainty in grain crop production are common in marginal semi-arid environments, such as East Nusa Tenggara province. Growing root and tuber crops in a mixed-cropping system is one of the strategies developed by smallholder farmers to substitute food grains and minimize risk. Nevertheless, root and tuber crops are not prioritized for food production systems since food crops in Indonesia are based more on grain and wetland rice production systems. This paper reviews cassava crops, which are widely cultivated by smallholder farmers. This paper contributes to understanding the roles of cassava for smallholder farmers, the diversity of the cassava germ plasm, the progress made to increase cassava productivity, and the potency of cassava crops to improve farmers’ incomes. This paper highlights that, in the low and erratic rainfall of dominant semi-arid regions, the development of cassava is pivotal to secure the harvest of food crops or food availability and income generation for marginal farmers.

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