Poultry manure application and fallow improves peanut production in a sandy soil under continuous cultivation

In PNG, agriculture supports the livelihood of more than 85% of the people who live mostly in the rural areas. Food security is therefore often perceived to be food secure; however, the lack of basic services and rural infrastructure indicate that most of the people are poor [1] and live far below the poverty line [2, 3];at 38% [4]. To meet the demands for food and the Government‟s Vision 2050 become a food secure country; policies need to be targeted at improving smallholder subsistence agriculture in the rural areas and integrate domestic markets to improve food security [5]. The peanut (A. hypogaea L.),is a cash crop that has a potentially high economic value [6, 7]. Peanut is high in protein and carbohydrates, and is a good source of food for human and livestock. In addition, peanut is rich in minerals like copper, manganese, potassium, calcium, iron, magnesium, zinc and selenium.

Reports show that peanut is the second most important oilseed crop cultivated inmost parts of the tropical, subtropical and warm temperate climate regions [8, 9]. In PNG, peanut is amongst the top five income generating cash crops [6]. Peanut is widely grown and marketed from the coastal lowlands to the mid–high altitude highlands of PNG, mainly in family owned subsistence farming systems. The crop has therefore become increasingly important as a cash crop and plays a significant role in family owned subsistence farming systems. Although the peanut has a high market potential, large-scale production in PNG is limited due to lack of high–yielding varieties, seed supply and suitable cost–effective farming practices [6]. The peanut, at the farm level has the ability to nourish soils, when grown in rotation or in combination with other food crops. As a result of rotation and/or intercropping, peanut has been implicated to increase yields of succeeding crops in rotation and/or component crops in intercrop systems. This is attributed to the activity of soil microbes that enhance productivity and quality of agricultural soils as a result of their influence on nutrient cycling, detoxification processes and soil aggregate stability, among other functions [10]. It has been reported that frequent use of peanut in crop rotation resulted in increase in soil–borne pathogens and relatively poor crop performance [11]. In continuous peanut cultivation systems, low peanut yields were associated with reductions in soil quality brought about by the changes in soil microbial community [12]. Continuous cultivation of peanut also reduced bacteria species and quantity of bacteria and actinomycetes, lower the number of fungi species and increase mould quantity [13]. Similar effects have been reported in peanut by [14; 15] and in cucumber by [16]. One of the reasons for continuous cultivation in tropical regions is population pressure on land.

The global human population grows at an annual rate of 1.7% and it is projected to double at this rate in 40 years. The [17] reported that PNG's annual population growth rate is 2.3%. This has resulted in the decline in productive arable croplands under cultivation and farming communities have resorted to continued cultivation on existing croplands. The practice of continuous crop cultivation on the same piece of land has led to rapid nutrient mining and it is believed to be more severe in the tropical regions. In PNG and most parts of the tropics, shifting cultivation and bush fallow systems were practiced to restore soil fertility; however, fallow periods are shorter now due to increasing pressure on existing cropland by rapid increases in population. On a global scale, the degradation of the soil physical, chemical and biological properties is a major concern as 40% of agricultural land degradation is induced by anthropogenic processes [18]. Although the peanut industry is not fully developed in PNG, peanut can be used as an alternative cash crop in crop rotation and/or intercropping systems to improve soil quality.

This paper reports the results of afield experiment conducted under rainfed conditions in four (4) different land use systems focused particularly on continuous peanut cultivation over a period of three (3) consecutive cropping seasons. The objectives were two fold; evaluate (i) the effects of continuous peanut cultivation system compared to peanut/corn rotation, and (ii) poultry manure and fallow LUS on peanut pod yield and on selected soil properties.