Table of Contents

Abstract: Ensuring food security is an ongoing global challenge. Many forecasts point to a need to increase food production by at least 70% if we are to feed the world’s projected population of nine billion in 2050. Recent volatility in commodity prices and the general upward trend in the cost of food are indicators that global food systems are now driven by demand rather than supply. There are various reasons for this: greater demand for animal protein with economic growth in developing countries; the continuing increase in world population; competition between food and bioenergy crops for land and water; low inventories of world grain stocks; reduced investment in agricultural R&D; and unfavorable weather resulting in a succession of poor harvests around the world. Increasing production of grains, which are the foundation of the human food supply, will have to be achieved through higher crop yields without boosting inputs of land, water and energy. Meeting community expectations for environmental stewardship and sustainability, and adapting food production to increasingly variable climate, add greatly to the challenge.

Abstract: Significant amounts of manure are produced in the USA; however, information on the changes in ecosystem services related to soil biogeochemical cycling for agroecosystems supported with organic amendments such as manure is limited. A multi-location field study was initiated in Colorado (CO), Kansas (KS) and Kentucky (KY), USA in loam soils to evaluate the effects of manure and tillage practices on enzyme activities that are key to biogeochemical cycling such as β-glucosidase (C cycling), α-galactosidase (C cycling), β-glucosaminidase (C and N cycling) and phosphomonoesterases (P cycling). The treatments were as follows: (i) two years of beef manure applications to a fine sandy loam at different rates (control: 0, low: 34 kg N ha⁻¹ and high: 96 kg N ha⁻¹) and tillage practices in CO; (ii) three years of beef manure applications to a silt loam at different rates (0, low: 67 kg N ha⁻¹ and high: 134 kg N ha⁻¹) and tillage practices in KS and; (iii) three years of poultry and dairy manure applications to a silt loam with different tillage practices at the same rate (403 kg N ha⁻¹) in KY. Tillage practices (none vs. conventional) had no effect on the enzyme activities. Principal Component Analyses (PCA) grouped all enzyme activities with the high beef manure application rate after the first year in CO at 0–5 cm. By the second year, the low and high beef manure rates differed in enzyme activities for the KS soil with no difference between the low rate and control in CO. Since the first year of the KY study, acid phosphatase activity was greater in the poultry treated soil compared to dairy or the control; whereas, C cycling enzyme activities were similar in soil treated with dairy or poultry manure. For all studies, PCAs for soil samples from 5–10 cm depth did not reveal treatment separation until the second year, i.e., only high application rate differed from the other treatments. Results of the study indicated significant responses in C and P cycling enzyme activities to manure applications within two years, suggesting potential benefits to soil biogeochemical cycling essential for the productivity of agroecosystems supported with organic fertilizers.

Abstract: This study was aimed at quantifying soybean (Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope ¹⁵N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. This study quantified N in abscised soybean leaves. Soybean-N derived from the atmosphere (%NDfA) ranged between 41–65%; it was higher (P < 0.05) in RT (55.6%) than in CT (46.6%). Total fixed-N under ‘RT + CR’ was more than in the other treatments by at least 55% in intercropping and 34% in rotation system. Nitrogen fixed in soybean aboveground parts was 26–48 kg N ha⁻¹ with intercropping and 53–82 kg N ha⁻¹ with rotation. Seasonal litter fall contained about 15 kg N ha⁻¹, with 54% NDfA. Annual nitrogen balances with soybean and maize grain removed were better in RT (−9 to −32 kg N ha⁻¹) than in CT (−40 to −60 kg N ha⁻¹). Application of P increased nodule weight (P < 0.05) by 3 to 16 times over the control. Soybean residues should be returned to the field after harvest to reduce soil N mining. We conclude that ‘RT + CR’ increases biological nitrogen fixation in soybean, over CT, and that phosphorus application is needed for better soybean nodulation in western Kenya.