Productivity and profitability of upland crop rotations in Northwest Cambodia
The upland cropping region of Northwest Cambodia exhibits limited crop diversity, with maize and cassava dominating rain-fed production systems. Farmers in the Districts of Sala Krau in Pailin Province, and Samlout in Battambang Province, report soil fertility decline in upland cropping systems with associated reduced yields and profitability compared with five years ago. Research was conducted at one site in each of these Districts over a two year period. The purpose of the study was to investigate crop rotations in this system with a focus on better use of soil water throughout the year to increase crop yields and profitability. This included an experiment to investigate increasing cropping intensity from the usual two crops per year to three and evaluate which crop sequences would be feasible. Out of a total 15 crop sequences evaluated, only four were successful in producing viable grain yields. These were the same sequences at both sites and included maize-maize-fallow, maize-maize-sunflower, maize-soybean-fallow and maizesoybean-sunflower. At Pailin, the sequence with the highest overall mean yield (4.3 t/ha) and profit was maize-maize-sunflower which returned a gross margin of $USD3700/ha over two years. The sequences with a fallow instead of a third crop produced the lowest financial returns at Pailin. However, in Samlout the maize-fallow was the most profitable sequence with an overall mean yield of 3.0 t/ha, returning $1680/ha over two years. The least profitable sequences at Samlout were the two soybean sequences. This study was successful in growing five crops in two years at Pailin, but could not reach the goal of six due to cultivar maturity length. At Samloutfour crops over two years were produced, as the pre-monsoon crop was not planted in either year due to lack of sowing rainfall. Seasonal climatic factors had the greatest effect at both field sites on gross margins, which emphasized the importance of matching sowing date to rainfall to make better use of stored soil moisture to optimise yield and profitability. At Pailin, mean seasonal surface soil moisture, hundred seed weight and harvest index also impacted gross margin returns. This research validated the stability of maize in the farming system while sunflower should be further investigated in cropping sequences.
Yield Responses of Maize and Sunflower to Mulch under No-till Farming Conditions in Northwest Cambodia
Background: Upland farming in Northwest Cambodia experiences annual soil loss and erosion due to the combination of topography, monsoonal climate and plough based farming practices. This study investigated the potential for no-till farming as a more sustainable farming method in this region. Methodology: An experiment was conducted at two sites in neighbouring Northwest provinces to investigate the effects of varying rates (nil, 2.5, 5, 10 and 20 t ha¯¹) of maize ('Zea mays' L.) stover mulch on yields of maize and sunflower ('Helianthus annus') using no-tillage farming practices. Small plot replicated experiments were undertaken in the pre-monsoon and post-monsoon seasons. Results: The 5 t haG1 mulch treatment attained the highest yield in the pre-monsoonal maize trial. During the post-monsoon period maize yield increased by 0.4 t ha¯¹ with every 2.5 t of mulch applied, whereas nil mulch resulted in near crop failure. Post-monsoon sunflower failed to respond to mulch treatments at either site. The lack of response at the second site which received higher rainfall was probably due to mild seasonal conditions and adequate stored soil water. Maize was more responsive to mulch than sunflower in both seasons with mulch application increasing yield. Conclusion: Farmers who retain crop residues increase their chances of establishing a pre-monsoon crop and reduce the probability of crop failure. This study also demonstrated that a successful crop can be grown in the non-traditional sowing period of the post-monsoon. While farmers may not have the resources to justify applying mulch regularly, it is thought they may use the knowledge gained from this study to implement no-till farming practices and retain crop residues 'in situ'.
Influence of Temperature and Humidity Regimes on the Developmental Stages of Green Vegetable Bug, 'Nezara viridula' (L.) (Hemiptera: Pentatomidae) From Inland and Coastal Populations in Australia
Laboratory studies were conducted to assess impacts of temperature and humidity regimes on the development of Nezara viridula (L.) (Hemiptera: Pentatomidae) from inland and coastal populations in NSW, Australia. Four temperature regimes, 25±2ºC, 30±2ºC, 33±2ºC, and 36±2ºC and two humidity regimes, 40±10% and 80±10% RH were applied in the experiment with a constant photoperiod of 14:10 h (L:D). The developmental time of the nymphal stage of N. viridula significantly decreased with increasing temperature. Percentage nymphal survival significantly decreased with increasing temperature or high humidity (80% RH) regimes. Longevity of N. viridula adults declined with increasing temperature or high humidity regimes and female longevity was longer than males. High temperatures (30, 33 and 36ºC) or high humidity significantly reduced reproductive performance and capacity of N. viridula compared to low temperature (25ºC) or low humidity (40% RH). However, high humidity significantly increased egg hatchability of N. viridula compared with a low humidity regime. Interactions of temperature and humidity regimes significantly changed incubation period, adult longevity, mating frequency, pre-mating period, egg-mass size and egg hatchability of N. viridula. Interactions of population location (coastal or inland), temperature and humidity regimes significantly changed incubation period and pre-oviposition period of N. viridula. Temperature and humidity are important environmental factors for the development and reproduction of N. viridula. Higher temperatures shorten the length of nymphal duration, but reduce nymphal survival. The optimum temperature for the development and reproduction of N. viridula was 25ºC with 40 ± 10% RH. No differences in nymphal duration, nymphal survival, adult longevity or reproduction performance between inland and coastal N. viridula populations were found under different climate conditions. We show the importance of assessing all life-stages in the response to varying temperature and humidity regimes, especially in terms of assessing responses to climate change.